DC-DC converter control circuit and method with rapid abnormal protection and soft start smooth self-recovery functions

Abstract

The invention relates to a DC-DC converter control circuit and method with rapid abnormal protection and soft start smooth self-recovery functions. The control circuit comprises an abnormal protection and state locking holding circuit located on the primary side of the DC-DC converter and a soft start and self-reset circuit located on the secondary side of the DC-DC converter. By arranging an abnormal protection and state locking holding circuit, the system can respond to abnormal conditions such as under-voltage or receiving of a forbidding signal in an extremely short time (us level), thereby realizing immediate protection; by arranging the soft start and self-reset circuit, stable rise of output voltage is ensured, the problems of impact on circuit elements caused by overlarge current at the moment of starting, overshoot of the output voltage and the like are avoided, and when the circuit triggers an abnormal protection state, a rapid discharge loop is provided for a capacitor in the soft start circuit, so that the circuit is protected. The problem that reset of a soft start circuit in a traditional circuit is affected by a secondary load is solved, and it is ensured that when a system quits a protection state and is restarted, output voltage can be smoothly established.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and particularly to a control circuit and method for a DC-DC converter with fast abnormal protection and soft-start smooth self-recovery functions. Background Art

[0002] With the continuous development and improvement of switching power supply technology, in order to make the power supply work more stably, power supply voltage monitoring functions such as "under-voltage protection", "circuit inhibition", "soft start and self-reset" have become an essential link in the design and use of DC-DC converters for switching power supplies. The purpose of the power supply voltage monitoring function is to turn off and on the switching function of the DC-DC converter when the system triggers an abnormal protection state, to protect the DC-DC converter to work within a suitable input voltage range, and to achieve a smooth establishment process of the output voltage.

[0003] In order to avoid the jitter of the input voltage in the under-voltage protection interval or the jitter of the inhibition voltage, which causes the DC-DC controller to work repeatedly between the protection state and the recovery state, a current measure is to connect a filter capacitor in parallel with the lower resistor in the sampling circuit. When the input voltage fluctuates near the under-voltage point, the filter capacitor can effectively filter out voltage spikes and interference, avoiding the state repetition caused by voltage jitter. However, the filter circuit cannot ensure a smooth transition between the protection state and the recovery state. Because when the input voltage drops rapidly, due to the maintenance characteristic of the filter capacitor, the drop speed of the sampling voltage will lag far behind the drop speed of the input voltage, resulting in a lag in the actual protection state, and the DC-DC converter works outside the protection setting range. Another method to avoid the jitter of the protection execution state is to use hysteresis comparison control, and set the turn-on threshold and the under-voltage protection threshold respectively to control the jitter voltage within a certain range. This method can effectively prevent the repeated operation of the protection circuit caused by small-amplitude jitter of the sampling voltage, but it has poor effects on rapid large-amplitude jitter and interference within a short time.

[0004] On the other hand, when the system triggers abnormal protection and the input voltage returns to the normal working voltage within a short time, the traditional protection circuit immediately exits the protection state, and the DC-DC converter immediately starts working again. However, since the secondary soft-start reset circuit discharges (resets) the soft-start capacitor through the output load, the reset process is slow, and it is difficult for the soft-start circuit to be reset in a short time. When the DC-DC converter restarts working, there may be problems such as overshoot of the output voltage and even overvoltage stress.

[0005] Therefore, future designs need to further optimize the filter circuit, hysteresis control strategy, and soft-start reset mechanism to achieve a smoother transition of the protection state and a more reliable system recovery, thereby improving the overall performance and stability of the DC-DC converter. Summary of the Invention

[0006] To solve the deficiencies in the prior art, the object of the present invention is to provide a DC-DC converter control circuit and method with fast abnormal protection and soft start smooth self-recovery functions.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention relates to a DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery functions. The control circuit includes: an abnormal protection and state locking and holding circuit located on the primary side of the DC-DC converter and a soft start and self-reset circuit located on the secondary side of the DC-DC converter.

[0009] The abnormal protection and state locking and holding circuit includes a first voltage sampling unit, a first reference voltage unit, a comparator unit, a maintaining unit, an executing unit, and a prohibiting unit; the first voltage sampling unit is used to collect the input voltage of the DC-DC converter; the first reference voltage unit is used to provide a threshold voltage; the comparator unit is used to compare the output voltage of the first voltage sampling unit with the threshold voltage generated by the first reference voltage unit and provide voltage hysteresis control; the executing unit is used to control the DC-DC controller to turn off the PWM drive pulse; the maintaining unit is used to provide additional time protection and control the PWM drive to maintain a non-wave output state; the prohibiting unit is used to pull down the voltage of the comparator comparison point when prohibition occurs to achieve output prohibition.

[0010] The soft start and self-reset circuit includes: a second voltage sampling unit, a soft start unit, a soft start reset unit, a second reference voltage unit, and an operational amplifier unit; the second voltage sampling unit is used to sample the output voltage of the DC-DC converter; the second reference voltage unit is used to provide a threshold voltage as a reference voltage; the soft start unit is used to realize the slow establishment process of the reference voltage; the operational amplifier unit is used to compare the sampled voltage with the reference voltage and provide stable closed-loop control as an error amplifier; the soft start reset unit is used to provide a fast discharge circuit for the capacitor in the soft start unit to realize the reset of the soft start circuit when the circuit triggers the abnormal protection state.

[0011] As a further improvement of the above technical solution, the first voltage sampling unit adopts a voltage division network, including an upper voltage division resistor R1 and a lower voltage division resistor R2 connected in series; the first end of the upper voltage division resistor R1 is connected to the power supply V in , the second end of the upper voltage division resistor R1 is connected to the first end of the lower voltage division resistor R2, and the second end of the lower voltage division resistor R2 is grounded.

[0012] As a further improvement of the above technical solution, the first reference voltage unit includes a current limiting resistor R3 and a reference source Z1; the first end of the current limiting resistor R3 is connected to the power supply Vin, the second end of the current limiting resistor R3 is connected to the first end of the reference source Z1, and the second end of the reference source Z1 is grounded; one end of the current limiting resistor R3 is connected to the power supply Vin, the other end is connected to the reference source Z1, and the other end of the reference source Z1 is grounded.

[0013] As a further improvement of the above technical solution, the comparator unit includes a comparator U1 and a hysteresis resistor R4; the non-inverting input terminal of the comparator U1 is connected to the connection node between the upper voltage dividing resistor R1 and the lower voltage dividing resistor R2, and the inverting input terminal of the comparator U1 is connected to the connection node between the current limiting resistor R3 and the reference source Z1; the output terminal of the comparator U1 is connected to the non-inverting input terminal of the comparator U1 through the hysteresis resistor R4.

[0014] As a further improvement of the above technical solution, the maintaining unit includes a maintaining capacitor C1, a discharging resistor R5 and a discharging resistor R6; the first end of the maintaining capacitor C1 is connected to the power supply V cc ; the second end of the maintaining capacitor C1 is connected to the output terminal of the comparator unit, that is, connected to the output terminal of the first comparator U1; the first end of the discharging resistor R5 is connected to the power supply V cc , the second end of the discharging resistor R5 is connected to the first end of the discharging resistor R6, and the second end of the discharging resistor R6 is connected to the output terminal of the comparator unit, that is, connected to the output terminal of the first comparator U1.

[0015] As a further improvement of the above technical solution, the executing unit includes a switching transistor Q1, a switching transistor Q2 and a current limiting resistor R7; the base of the switching transistor Q1 is connected to the node between the discharging resistor R5 and the discharging resistor R6, the collector of the switching transistor Q1 is connected to the power supply V cc , the emitter of the switching transistor Q1 is connected to the first end of the current limiting resistor R7, the second end of the current limiting resistor R7 is connected to the base of the switching transistor Q2, the collector of the switching transistor Q2 is connected to the voltage V comp , and the emitter of the switching transistor Q2 is grounded.

[0016] As a further improvement of the above technical solution, the inhibiting unit includes an inverse diode D1; the anode of the inverse diode D1 is connected to the non-inverting input terminal of the comparator U1, and the cathode of the inverse diode D1 outputs an INH inhibit signal.

[0017] As a further improvement of the above technical solution, the second voltage sampling unit uses a voltage dividing network, including an upper voltage dividing resistor R D1 and a lower voltage dividing resistor R D2; The upper voltage-dividing resistor R D1 has its first end connected to the power supply Vo, and the second end of the upper voltage-dividing resistor R D1 is connected to the first end of the lower voltage-dividing resistor R D2 , and the second end of the lower voltage-dividing resistor R D2 is grounded.

[0018] As a further improvement of the above technical solution, the soft start unit includes a resistor Rss and a capacitor Css.

[0019] As a further improvement of the above technical solution, the second reference voltage unit includes a resistor R11 and a reference source N1. The first end of the resistor R11 is connected to the power supply V ccs , the second end of the resistor R11 is connected to the first end of the reference source N1, and the second end of the reference source N1 is grounded; the first end of the resistor Rss is connected to the anode of the diode D2, and the second end of the resistor Rss is connected to the node between the resistor R11 and the reference source N1; the first end of the capacitor Css is connected to the anode of the diode D2, and the second end of the capacitor Css is grounded.

[0020] As a further improvement of the above technical solution, the soft start reset unit includes a discharge resistor R10, a capacitor C v and a diode D2; the first end of the discharge resistor R10 is connected to the first end of the capacitor C v and then connected to the power supply V ccs , the second end of the discharge resistor R10 is connected to the second end of the capacitor C v and then grounded; the anode of the diode D2 is connected to the non-inverting input terminal of the operational amplifier U2, and the cathode of the diode D2 is connected to the power supply V ccs .

[0021] As a further improvement of the above technical solution, the operational amplifier unit includes an operational amplifier U2, a capacitor C FS , a capacitor C HS and a resistor R F ; the non-inverting input terminal of the operational amplifier U2 is connected to the anode of the diode D2, the inverting input terminal of the operational amplifier U2 is connected to the node between the resistor R D1 and the resistor R D2 , and the output terminal of the operational amplifier U2 outputs a voltage signal V EA ; the first end of the capacitor C FS is connected to the output terminal of the operational amplifier U2, the second end of the capacitor C FS is connected to the first end of the resistor R F , and the second end of the resistor R F is connected to the inverting output terminal of the operational amplifier U2; the capacitor CHS The first end of [component] is connected to the output terminal of the operational amplifier U2, and the capacitor C HS The second end of [component] is connected to the inverting input terminal of the operational amplifier U2.

[0022] The present invention also includes a control method for the above control circuit, and the method includes the following steps:

[0023] S1. Abnormality detection

[0024] On the primary side, the first voltage sampling unit continuously samples the input voltage of the DC-DC converter and transmits the sampled voltage to the non-inverting input terminal of the comparator U1 in the comparator unit. The first reference voltage unit outputs a first threshold voltage to the inverting input terminal of the comparator U1. The comparator U1 compares the sampled voltage with the first threshold voltage. If the sampled voltage is lower than the threshold voltage, it is determined to be an undervoltage state, and the comparator U1 outputs a low-level signal. In addition, the reverse diode D1 in the disabling unit conducts when receiving a low-level effective disabling signal, pulling down the voltage of the comparison point of the comparator U1, causing the comparator U1 to output a low-level signal.

[0025] S2. Abnormality protection and status locking maintenance

[0026] The low-level signal output by the comparator U1 activates the maintenance unit and the execution unit, triggering abnormality protection. In the maintenance unit, when the output of the comparator U1 is pulled low, the power supply Vcc quickly charges the maintenance capacitor C1, and the maintenance capacitor C1 maintains the protection state according to its charging characteristics, and the duration of maintaining the protection state is T3. In the execution unit, the low-level signal output by the comparator U1 turns on the switching transistor Q1, which in turn drives the switching transistor Q2 to turn on, and finally controls the DC-DC controller to turn off the PWM drive pulse and stop the operation of the DC-DC converter, so as to achieve fast abnormality protection for the DC-DC converter.

[0027] S3. Soft start

[0028] On the secondary side, the second voltage sampling unit continuously samples the output voltage of the DC-DC converter and transmits the sampled voltage to the inverting input terminal of the operational amplifier U2 in the operational amplifier unit. The second reference voltage unit outputs a second threshold voltage as the reference voltage of the operational amplifier U2. The soft start unit charges the capacitor Css through the resistor Rss, causing the reference voltage of the operational amplifier U2 to rise. This reference voltage serves as the reference signal for the operational amplifier U2 to control the DC-DC controller to output a driving waveform with a slowly expanding duty cycle, so as to limit the starting current and make the output voltage rise smoothly.

[0029] S4. Self-reset

[0030] When the system triggers abnormality protection, the secondary auxiliary power supply V of the DC-DC converterccs The supply voltage discharges and drops through the parallel discharge resistor R10. When it drops to a certain proportion, the reverse diode D2 in the soft start reset unit conducts, and the soft start capacitor Css discharges through the diode D2 to the discharge resistor R10 to reset the soft start circuit. The reset time is T2, where T2 is less than T3.

[0031] S5. System restart

[0032] If the input voltage of the DC-DC converter rises back and is greater than the turn-on threshold, and the maintenance time of the maintenance unit ends, the PWM controller starts to output drive pulses, the DC-DC converter restarts, performs a soft start power-on process, and the output voltage is smoothly established, and the system resumes normal operation.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] (1) By setting an abnormal protection and state locking and holding circuit on the primary side of the DC-DC converter, the present invention can respond to abnormal conditions such as undervoltage or receiving a prohibit signal within an extremely short time (in the order of microseconds). The comparator U1 quickly performs a state flip, controls the protection execution unit to turn off the PWM drive pulse, and realizes immediate protection. The maintenance unit utilizes the charge and discharge characteristics of the maintenance capacitor C1 to provide an additional protection time, ignoring the fluctuations of the sampled voltage during the protection time, maintaining the protection state for a set time length, and avoiding frequent startup and shutdown of the circuit due to short-term voltage fluctuations. Through the coordinated work of the maintenance capacitor C1 and the soft start and self-reset circuit, no matter how quickly the input voltage or the prohibit signal fluctuates, as long as the minimum maintenance time is set, it can ensure that the DC-DC converter has sufficient reset duration, greatly improving the reliability of the DC-DC converter.

[0035] (2) The present invention sets a soft start and self-reset circuit on the secondary side of the DC-DC converter. Among them, the soft start unit charges the capacitor Css through the resistor Rss, slowly establishing the reference voltage, limiting the startup current, ensuring the smooth rise of the output voltage, and avoiding problems such as excessive current at the moment of startup impacting circuit components and overshoot of the output voltage. When the circuit triggers the abnormal protection state, the soft start reset unit provides a fast discharge loop for the capacitor in the soft start circuit, solving the problem that the reset of the soft start circuit in the traditional circuit is affected by the secondary load, and ensuring that when the system exits the protection state and restarts, the output voltage can be smoothly established. In addition, the present invention also realizes the complete reset of the soft start and self-reset circuit during the protection period through the timing control of the internal circuit, and the reset process of the soft start is not affected by the change of the external working state. During the T3 time when the protection state is maintained on the primary side, the secondary soft start capacitor C SS quickly discharges to the resistor R10 through the diode D2, reducing the soft start circuit reset time. Description of the Drawings

[0036] Figure 1 is the principle block diagram of the DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery functions in the present invention;

[0037] Figure 2 is the circuit schematic diagram of the DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery functions in the present invention;

[0038] Figure 3 is the circuit schematic diagram of the abnormal protection and state locking and holding circuit in the present invention;

[0039] Figure 4 is the circuit schematic diagram of the soft start and self-reset circuit in the present invention;

[0040] Figure 5 is the circuit schematic diagram of the LM119 operational amplifier;

[0041] Figure 6 is the circuit diagram of the traditional reset circuit;

[0042] Figure 7 is the soft start reset waveform diagram under large capacitive load conditions;

[0043] Figure 8 is the soft start process waveform diagram under different holding times T3;

[0044] Figure 9 is the simulation waveform diagram of the traditional circuit under input voltage jitter;

[0045] Figure 10 is the simulation waveform diagram of the control circuit in the present invention under input voltage jitter;

[0046] Figure 11 is the simulation waveform diagram of the traditional circuit under prohibited voltage jitter;

[0047] Figure 12 is the simulation waveform diagram of the control circuit in the present invention under prohibited voltage jitter;

[0048] Figure 13 is the protection timing diagram of the abnormal state protection circuit of the ordinary hysteresis comparator;

[0049] Figure 14 is the protection timing diagram of the abnormal protection and state locking and holding circuit in the present invention. Detailed Embodiments

[0050] The present invention will be further described below with reference to the accompanying drawings:

[0051] The present invention relates to a DC-DC converter control circuit and method with fast abnormal protection and soft start smooth self-recovery functions for a switching power supply.

[0052] Figure 1 And Figure 2 The schematic diagram of a switching power supply using the DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery functions described in the present invention is given. As Figure 1 And Figure 2 shown, the switching power supply includes a DC-DC converter, an input filter circuit, a PWM controller, a power circuit, an isolation circuit, a soft start and self-reset circuit, and an abnormal protection and status locking and holding circuit. The power circuit and the isolation circuit adopt existing technologies.

[0053] As Figure 1 shown, the DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery functions described in the present invention includes an abnormal protection and status locking and holding circuit on the primary side of the DC-DC converter and a soft start and self-reset circuit on the secondary side of the DC-DC converter. Through the two circuits, fast abnormal protection and soft start smooth self-recovery of the DC-DC converter are realized. The abnormal protection and status locking and holding circuit is located on the primary side of the DC-DC converter. On the one hand, it is used to implement the under-voltage protection / prohibition function to prevent the circuit from continuing to work when the input voltage is too low or a prohibition signal is received; on the other hand, it is used to implement status locking to ensure that a certain time is maintained in the protection state to avoid frequent switching of the protection state due to factors such as voltage fluctuations.

[0054] In this embodiment, whether it is the abnormal protection and status locking and holding circuit on the primary side or the soft start and self-reset circuit on the secondary side, through reasonable circuit design and parameter configuration, the influence of external factors (such as voltage fluctuations, load changes, etc.) on the circuit operation is reduced, and it has strong anti-interference ability. And multiple circuit units are all composed of simple components such as resistors, capacitors, diodes, and reference sources. For example, the voltage sampling unit adopts a voltage division network, and the soft start unit utilizes the capacitor charging characteristic, etc. While realizing complex functions, the cost of the circuit is reduced.

[0055] As a further improvement of the above technical solution, the abnormal protection and status locking and holding circuit is used to send a driving wave to control the PWM controller based on the value of the input voltage VIN. As Figure 3 shown, the abnormal protection and status locking and holding circuit includes a first voltage sampling unit, a first reference voltage unit, a comparator unit, a maintaining unit, an executing unit, and a prohibiting unit. The abnormal protection and status locking and holding circuit is used to implement the under-voltage protection / prohibition function on the one hand and status locking on the other hand.

[0056] Specifically, the first voltage sampling unit is used to collect the input voltage of the DC-DC converter; the first reference voltage unit is used to provide a threshold voltage; the comparator unit is used to compare the output voltage of the first voltage sampling unit with the threshold voltage generated by the first reference voltage unit and provide voltage hysteresis control; the execution unit is used to control the DC-DC controller to turn off the PWM drive pulse; the maintenance unit is used to provide additional time protection, that is, to ignore the fluctuation of the sampled voltage during the protection time and maintain the protection state for a set time length, that is, to control the PWM drive to remain in a non-wave state; the prohibition unit is used to pull down the voltage of the comparator comparison point when prohibition occurs to achieve output prohibition. The maintenance unit and the execution unit together constitute a protection execution unit.

[0057] As a further improvement of the above technical solution, the first voltage sampling unit adopts a voltage dividing network, including an upper voltage dividing resistor R1 and a lower voltage dividing resistor R2 connected in series; the first end of the upper voltage dividing resistor R1 is connected to the power supply V in , the second end of the upper voltage dividing resistor R1 is connected to the first end of the lower voltage dividing resistor R2, and the second end of the lower voltage dividing resistor R2 is grounded. The first voltage sampling unit samples the input voltage of the DC-DC converter through the principle of resistor voltage division. The sampled voltage is the value obtained by distributing the input voltage according to the resistance ratio of R1 and R2, and is transmitted to the non-inverting input terminal of the comparator U1 of the comparator unit 3.

[0058] The present invention realizes voltage sampling through a simple voltage dividing network, with low cost and high reliability. Through the first voltage sampling unit, the real-time information of the input voltage of the DC-DC converter can be accurately obtained, providing a basis for subsequent undervoltage protection judgment, ensuring that the protection action can be triggered in time when the input voltage is lower than the set threshold, and guaranteeing the safety of the circuit. During the implementation process, since the accuracy and stability of the resistor will affect the accuracy of the sampled voltage, it is necessary to select resistors with appropriate accuracy and temperature coefficient.

[0059] As a further improvement of the above technical solution, the first reference voltage unit includes a current limiting resistor R3 and a reference source Z1; the first end of the current limiting resistor R3 is connected to the power supply Vin, the second end of the current limiting resistor R3 is connected to the first end of the reference source Z1, and the second end of the reference source Z1 is grounded. The first reference voltage unit is used to provide a stable threshold voltage for the comparator, ensuring the accuracy of the comparison result, and thus reliably triggering the protection action.

[0060] Specifically, one end of the current limiting resistor R3 is connected to the power supply Vin, and the other end is connected to the reference source Z1, and the other end of the reference source Z1 is grounded. The power supply Vin provides a suitable working current to the reference source Z1 through the current limiting resistor R3, and the reference source Z1 outputs a stable threshold voltage, which is connected to the reverse input terminal of the comparator U1 of the comparator unit. The first reference voltage unit provides a stable and accurate threshold voltage for the comparator U1 as a reference standard for judging whether the input voltage is normal, ensuring the accuracy of the comparison result, thereby reliably triggering the protection action.

[0061] Compared with the common voltage divider circuit, the present invention uses a reference source to provide the threshold voltage, which can effectively reduce the influence of power supply fluctuation, temperature change and other factors on the threshold voltage, and improve the stability and accuracy of the threshold voltage. The selection of the reference source Z1 is very important, and its output accuracy, temperature characteristics, long-term stability and other parameters need to be considered. At the same time, the value of the current limiting resistor R3 should be appropriate. If it is too large, the working current of the reference source Z1 may be insufficient, and if it is too small, the power consumption may be too large, affecting the circuit efficiency.

[0062] As a further improvement of the above technical solution, the comparator unit includes a comparator U1 and a hysteresis resistor R4; the same-direction input terminal of the comparator U1 is connected to the connection node between the upper voltage-dividing resistor R1 and the lower voltage-dividing resistor R2, and the reverse input terminal of the comparator U1 is connected to the connection node between the current-limiting resistor R3 and the reference source Z1; the output terminal of the comparator U1 is connected to the same-direction input terminal of the comparator U1 via the hysteresis resistor R4.

[0063] The comparator unit compares the output voltage of the first voltage sampling unit with the threshold voltage generated by the first reference voltage unit, and outputs a corresponding signal according to the comparison result to control the action of the protection execution unit. When the sampling voltage is greater than the threshold voltage, it outputs a logic high level; when the sampling voltage is lower than the threshold voltage, it outputs a logic low level. The output voltage of the comparator U1 is V o1 The comparator U1 generates a comparison state, has a first comparator state when the sampling voltage is greater than the threshold voltage, and has a second comparator state when the sampling voltage is lower than the threshold voltage. In the fast abnormal protection and state lock holding circuit, the comparison state can be alternately converted: in the non-undervoltage state, the sampling voltage is greater than the threshold voltage, and the comparator U1 outputs a logic high level; in the undervoltage / disabled state, the sampling voltage is lower than the threshold voltage, and the comparator U1 outputs a logic low level.

[0064] The comparator unit realizes voltage hysteresis control by introducing hysteresis resistor R4, thereby enhancing the anti-interference ability of the circuit. Hysteresis resistor R4 is connected between the output terminal and the same-direction input terminal of the comparator U1 to realize voltage hysteresis control. Due to the existence of hysteresis control, the output state conversion of the comparator has a certain hysteresis.

[0065] The present invention effectively improves the tolerance of the protection circuit to voltage fluctuations through a simple circuit structure, reduces the possibility of false triggering, and can avoid frequent switching of the comparator output due to small fluctuations in the input voltage through hysteresis control, thereby improving the stability of the protection. During the implementation of this embodiment, it should be noted that the value of the hysteresis resistor R4 needs to be accurately calculated and adjusted according to the specific circuit requirements to achieve an appropriate hysteresis width. If the resistance value is too large, the hysteresis width will be too large, which may cause the protection action to be untimely; if the resistance value is too small, the hysteresis width will be too small, and it will not be able to effectively avoid false triggering caused by voltage fluctuations.

[0066] As a further improvement of the above technical solution, the maintaining unit includes a maintaining capacitor C1, a discharging resistor R5, and a discharging resistor R6; the first end of the maintaining capacitor C1 is connected to the power supply V cc ; the second end of the maintaining capacitor C1 is connected to the output end of the comparator unit, that is, connected to the output end of the first comparator U1; the first end of the discharging resistor R5 is connected to the power supply V cc , the second end of the discharging resistor R5 is connected to the first end of the discharging resistor R6, and the second end of the discharging resistor R6 is connected to the output end of the comparator unit 3, that is, connected to the output end of the first comparator U1.

[0067] The maintaining unit is used to control the minimum protection maintaining time to ensure that after detecting an abnormality (such as undervoltage or receiving a prohibition signal), the protection state can be maintained for a set time length, thereby avoiding frequent switching of the protection state due to fluctuations in the sampling voltage within a short period of time, and ensuring the stability and reliability of the circuit. When the comparator U1 outputs a low level, the power supply Vcc quickly charges the maintaining capacitor C1; when the comparator U1 outputs a high level, the maintaining capacitor C1 discharges through the discharging resistors R5 and R6.

[0068] The maintaining unit utilizes the charging and discharging characteristics of the capacitor C1 to achieve the maintenance of the protection state, without a complex logic control circuit, with a simple structure and low cost. Since the charging current of the maintaining capacitor C1 is relatively large, on the one hand, it will increase the power consumption of the circuit, and on the other hand, it may affect the normal working performance of the chip. Therefore, the present invention requires creative labor to reasonably select the parameters of the capacitor and resistor to balance the relationship between the protection maintaining time and the circuit performance.

[0069] As a further improvement of the above technical solution, the executing unit includes a switching transistor Q1, a switching transistor Q2, and a current limiting resistor R7; the base of the switching transistor Q1 is connected to the node between the discharging resistor R5 and the discharging resistor R6, and the collector of the switching transistor Q1 is connected to the power supply V cc, the emitter of the switching transistor Q1 is connected to the first end of the current-limiting resistor R7, the second end of the current-limiting resistor R7 is connected to the base of the switching transistor Q2, and the collector of the switching transistor Q2 is connected to the voltage V comp , the emitter of the switching transistor Q2 is grounded. The collector of the switching transistor Q2 and Figure 1 / Figure 2 is connected to the COMP terminal of the PWM controller in the[ / ], or a similar functional terminal. After being pulled low, the PWM controller does not work / does not generate waves.

[0070] When the capacitor C1 of the maintenance unit is charged to enable the base of the switching transistor Q1 to obtain sufficient driving voltage, the switching transistor Q1 conducts, and then the switching transistor Q2 conducts, controlling the DC-DC controller to turn off the PWM driving pulse. After the comparator U1 outputs an abnormal signal and is maintained for a certain time by the maintenance unit, the DC-DC controller is quickly controlled to turn off the PWM driving pulse, stopping the operation of the DC-DC converter, and realizing the protection of the circuit.

[0071] The maintenance unit of the present invention adopts a two-stage switching transistor control structure, which can effectively enhance the driving ability, ensure reliable turning off of the PWM driving pulse, and improve the timeliness and reliability of protection. During implementation, the selection of the switching transistors Q1 and Q2 needs to consider parameters such as their withstand voltage, current-carrying capacity, and switching speed. If the parameters are selected improperly, it may cause the switching transistors to not work properly, such as being unable to conduct or generating excessive losses when conducting, affecting the performance of the protection circuit.

[0072] As a further improvement of the above technical solution, the prohibition unit includes a reverse diode D1; the anode of the reverse diode D1 is connected to the non-inverting input terminal of the comparator U1, and the cathode of the reverse diode D1 outputs the INH prohibition signal.

[0073] In this embodiment, the first voltage sampling unit forms an undervoltage protection circuit, and the prohibition unit forms a prohibition circuit. The prohibition circuit and the undervoltage protection circuit share the same comparator. By simply pulling down the voltage of the sampling point with the reverse diode D1, the output prohibition function is realized, thus saving circuit cost and space and improving the circuit integration.

[0074] The present invention provides an additional protection mechanism that can actively prohibit the circuit output when receiving a specific prohibition signal, enhancing the safety and controllability of the circuit. When receiving a valid prohibition signal (low level valid), the reverse diode D1 conducts, pulling down the voltage of the comparison point of the comparator U1, changing the output state of the comparator U1, just like being in an undervoltage state, and then triggering the protection execution unit to act.

[0075] When the sampled voltage is lower than the threshold voltage, the output voltage of the comparator U1 flips, and the protection execution unit works in the following manner:

[0076] (1) Immediately control the PWM controller to turn off the PWM drive pulses;

[0077] (2) Provide a minimum protection maintenance time setting to ignore the change in the comparator output state caused by the fluctuation of the sampled voltage within a short period, maintain the continuous protection state within the minimum time, and block the PWM drive for the reset of the primary and secondary soft-start circuits of the switching power supply.

[0078] During the implementation of the disabling unit, it is necessary to ensure the effectiveness and stability of the disabling signal, and the on and off characteristics of the reverse diode D1 meet the circuit requirements. If there is interference in the disabling signal or the diode characteristics are poor, it may lead to mis-triggering or abnormal disabling of the output.

[0079] As a further improvement of the above technical solution, as Figure 4 shown, the soft start and self-reset circuit includes: a second voltage sampling unit, a soft start unit, a soft start reset unit, a second reference voltage unit, and an operational amplifier unit. The second voltage sampling unit is used to sample the output voltage of the DC-DC converter. The second reference voltage unit is used to provide a threshold voltage as the reference voltage. The soft start unit is used to realize the slow establishment process of the reference voltage. The soft start unit slowly establishes the reference voltage through capacitor charging, limits the start current, ensures the smooth rise of the output voltage, and cooperates with other units to ensure the stable start of the DC-DC converter and its smooth restart after an abnormality. The operational amplifier unit is used to compare the sampled voltage with the reference voltage, provide stable closed-loop control as an error amplifier, and provide a stable output. The operational amplifier U2 generates a comparison state and controls the DC-DC controller to output drive waveforms in different states according to the comparison state to maintain the stability of the output voltage. The soft start reset unit is used to provide a fast discharge circuit for the capacitor in the soft start circuit to quickly reset the soft start circuit when the circuit triggers an abnormal protection state, and avoid the abnormality that may occur when the DC-DC controller restarts within a short period.

[0080] As a further improvement of the above technical solution, the second voltage sampling unit adopts a voltage division network, including an upper voltage division resistor R D1 and a lower voltage division resistor R D2 ; the first end of the upper voltage division resistor R D1 is connected to the power supply Vo, the second end of the upper voltage division resistor R D1 is connected to the first end of the lower voltage division resistor R D2 , and the second end of the lower voltage division resistor R D2 is grounded.

[0081] The second voltage sampling unit samples the output voltage of the DC-DC converter through the principle of resistor voltage division. The sampled voltage is the value obtained by distributing the output voltage according to the resistance ratio of RD1 and RD2, and it is transmitted to the inverting input terminal of the operational amplifier U2 in the operational amplifier unit. The second voltage sampling unit obtains the information of the output voltage of the DC-DC converter in real time, providing a basis for subsequent comparison and control to maintain the stability of the output voltage. Similar to the first voltage sampling unit, the second voltage sampling unit uses a simple resistor voltage division network to implement voltage sampling, which has the advantages of simple structure and low cost.

[0082] As a further improvement of the above technical solution, the soft start unit includes a resistor Rss and a capacitor Css. The soft start unit utilizes the charging characteristic of the capacitor Css to achieve the slow establishment of the reference voltage, thereby realizing the soft start function. The principle is simple and the effect is remarkable, without the need for a complex control circuit.

[0083] Specifically, when the circuit starts, the power supply charges the capacitor Css through the resistor Rss, and the voltage across the capacitor Css gradually increases, thereby slowly establishing the reference voltage. This slowly rising reference voltage serves as the reference signal for the operational amplifier U2, controlling the DC-DC controller to output drive waveforms in different states, so that the output voltage rises smoothly. The soft start unit avoids the impact on components caused by excessive current at the moment of circuit startup and problems such as overshoot of the output voltage, ensuring that the output voltage can be established smoothly and slowly, improving the reliability and stability of the circuit. The parameter selection of the resistor Rss and the capacitor Css needs to be accurately calculated according to the specific circuit requirements. If the parameter selection is improper, it may lead to too long or too short soft start time, affecting the normal startup and working performance of the circuit.

[0084] As a further improvement of the above technical solution, the second reference voltage unit includes a resistor R11 and a reference source N1. The first end of the resistor R11 is connected to the power supply V ccs , the second end of the resistor R11 is connected to the first end of the reference source N1, and the second end of the reference source N1 is grounded; the first end of the resistor Rss is connected to the anode of the diode D2, and the second end of the resistor Rss is connected to the node between the resistor R11 and the reference source N1; the first end of the capacitor Css is connected to the anode of the diode D2, and the second end of the capacitor Css is grounded.

[0085] Power supply V ccsA suitable operating current is provided to the reference source N1 through the resistor R11. The reference source N1 outputs a stable threshold voltage as the reference voltage of the operational amplifier U2, providing a stable and accurate reference voltage for the operational amplifier U2, thereby ensuring that the operational amplifier U2 can accurately compare the sampled voltage and the reference voltage, and further realizing the stable control of the output voltage. The present invention uses the reference source N1 to provide the reference voltage, improving the stability and accuracy of the reference voltage and reducing the influence of power supply fluctuations and temperature changes on the reference voltage.

[0086] As a further improvement of the above technical solution, the soft start reset unit includes a discharge resistor R10, a capacitor C v and a diode D2; the first end of the discharge resistor R10 is connected to the first end of the capacitor C v and then connected to the power supply V ccs , the second end of the discharge resistor R10 is connected to the second end of the capacitor C v and then grounded; the anode of the diode D2 is connected to the non-inverting input terminal of the operational amplifier U2, and the cathode of the diode D2 is connected to the power supply V ccs .

[0087] The soft start reset unit solves the problem that the soft start circuit reset in the traditional circuit is affected by the secondary load, and can quickly realize the reset of the soft start circuit after the circuit triggers abnormal protection, ensuring that when the system exits the protection state and restarts, the output voltage can be smoothly established, avoiding abnormal situations such as overshoot or jitter. When the circuit triggers the abnormal protection state, the supply voltage of the secondary auxiliary power supply V ccs of the DC-DC converter discharges and drops through the parallel discharge resistor R10. When the voltage drops to a certain ratio, the diode D2 conducts, and the soft start capacitor Css quickly discharges through the diode D2 to the discharge resistor R10, realizing the reset of the soft start circuit. The soft start reset unit designs a special fast discharge circuit, making the reset process of the soft start circuit not affected by the change of the external working state, having strong anti-interference ability, and improving the reliability and stability of the circuit. During the implementation process, it is necessary to reasonably configure the parameters of the discharge resistor R10, the capacitor Css and the diode D2 to ensure the effective discharge of the soft start capacitor Css within the specified time. At the same time, the conduction voltage drop and reverse cut-off characteristics of the diode D2 should be considered to avoid affecting the normal operation.

[0088] As a further improvement of the above technical solution, the operational amplifier unit 9 includes an operational amplifier U2, a capacitor C FS , a capacitor C HS and a resistor R F ; the non-inverting input terminal of the operational amplifier U2 is connected to the anode of the diode D2, and the inverting input terminal of the operational amplifier U2 is connected to the resistor R D1is connected to the node between it and the resistor R D2 ; the output terminal of the operational amplifier U2 outputs a voltage signal V EA ; the first end of the capacitor C FS is connected to the output terminal of the operational amplifier U2, and the second end of the capacitor C FS is connected to the first end of the resistor R F ; the second end of the resistor R F is connected to the inverting output terminal of the operational amplifier U2; the first end of the capacitor C HS is connected to the output terminal of the operational amplifier U2, and the second end of the capacitor C HS is connected to the inverting input terminal of the operational amplifier U2.

[0089] The operational amplifier unit 9 adjusts the driving waveform of the DC-DC controller according to the comparison result by comparing the sampled voltage and the reference voltage in real time, so that the output voltage is maintained within a stable range, improving the output accuracy and stability of the circuit. The operational amplifier unit 9 is also used for loop compensation. The operational amplifier U2 compares the sampled voltage with the reference voltage and outputs different voltage signals according to the comparison result to control the DC-DC controller to output driving waveforms in different states and maintain the output voltage stable. The capacitor C FS , the capacitor C HS and the resistor R F constitute a feedback network, which is used to improve the stability and dynamic response characteristics of the comparator, dynamically adjust the output of the comparator, improve the performance and control accuracy of the comparator, and enable the circuit to better adapt to different working conditions. The existence of the feedback network enhances the anti-interference ability and dynamic response performance of the comparator. The parameters of the feedback network need to be precisely adjusted according to the specific circuit requirements to achieve the best control effect. The values of the capacitor and resistor will affect the feedback strength and frequency response characteristics. If the parameters are not appropriate, problems such as circuit oscillation and slow response may occur.

[0090] Compared with the traditional abnormal protection circuit, the present invention overcomes the biggest defect of the traditional protection circuit. The traditional protection circuit realizes the reset of the soft start circuit by means of the secondary load. The working state of the soft start circuit is greatly affected by the secondary working state. When the sampling voltage jitters rapidly, the protection circuit alternately executes "protection - non - protection - protection..." execution jitters. The large capacitive load existing in the secondary will cause the soft start circuit not to be fully reset when the system exits the protection state, and there will be output voltage overshoot and even over - voltage stress problems when working again. The present invention realizes the full reset of the soft start circuit during protection through the timing control of the internal circuit. The reset process of the soft start is not affected by the change of the external working state, has strong anti - interference ability, and can ensure that when the system exits the protection state and starts to work under any circumstances, the secondary can obtain a fully reset soft start circuit.

[0091] The traditional secondary soft start reset circuit connects the soft start capacitor to the output voltage through a diode and discharges (resets) the soft start circuit through the output load as Figure 6 shown by the red circuit in Figure 6 The reset circuit in Figure 7 can generally realize the normal reset function, but the problem of this circuit is that when there is a large capacitive load in the secondary, the output voltage drops slowly, and the discharge of the soft start capacitor also becomes slow, and the soft start capacitor in the soft start circuit cannot be fully reset in a short time. Moreover, when abnormal protection occurs and the DC - DC controller restarts in a short time, due to the soft start circuit without complete reset, the output voltage is not established smoothly, and there may be overshoot or mid - way drop as

[0092] shown in

[0093] (1) Case 1

[0094] T1≥T2. When abnormal protection is triggered and restarted, the secondary has effectively completed the soft start reset, and the start is smooth and there is no overshoot at this time.

[0095] (2) Case 2

[0096] T1<T2. When abnormal protection is triggered and restarted, the secondary has not effectively realized the reset of the soft start capacitor. At this time, the soft start capacitor is recharged, which will cause the output start to be not smooth, and there are overshoot / jitters as Figure 8 shown in

[0097] Based on the deficiencies existing in the above-mentioned prior art, two circuits are designed on the primary and secondary sides of the DC-DC converter of the present invention to eliminate the influence of external factors of the system on the circuit, and through the timing control of the internal circuit of the system, the problems occurring in the above-mentioned second situation are solved.

[0098] (1) On the primary side of the DC-DC converter, an abnormal protection and state locking and holding circuit as shown in Figure 3 is designed. After abnormal protection such as prohibition or undervoltage occurs, the comparator U1 performs state flipping within an extremely short time (in the order of microseconds) to achieve immediate protection. Figure 3 The capacitor C1 in CC is a state locking and holding capacitor, and the protection state is maintained by the capacitor characteristics for a duration of T3, that is, T3 represents the duration of maintaining the protection state on the primary side. It should be noted that the comparator U1 often adopts an open-drain output amplifier (such as LM119). When V CC = 9V and charging, the charging current for maintaining the capacitor C1 reaches about 3A. On the one hand, the larger charging current will increase the circuit loss, and on the other hand, it will affect the normal working performance of the chip. Therefore, the setting of the T3 time needs to comprehensively consider its rationality. In this embodiment, the T3 is calculated by formula (1):

[0099]

[0100] In formula (1), R is the equivalent discharge resistance of the capacitor C1, and the value of R is approximately R5 + R6. V CB_ON is the PN junction voltage drop of the PNP triode. When the VCC voltage drops and the voltage across the resistor R5 is lower than the PN junction voltage drop, the PNP triode will stop conducting and the maintenance time ends.

[0101] (2) On the secondary side of the DC-DC converter, a secondary soft start and self-reset circuit as shown in Figure 4 is designed.

[0102] Under normal conditions, the soft start time is about in the order of 20ms. Therefore, the time constant of the resistor R SS and the capacitor C SS is relatively large, and it takes too long to discharge the soft start capacitor Css through the resistor R SS . During the T3 time of maintaining the protection state on the primary side, in the circuit designed in this embodiment, the secondary soft start capacitor C SS discharges to the resistor R10 through the diode D2 to reduce the reset time of the soft start circuit. After improving the discharge loop, rapid discharge is performed through the diode D1 and the discharge resistor R10, and the parameters of the soft start circuit are reasonably configured, so that within the T3 time, effective discharge of the capacitor C SS and the capacitor C V can be achieved. Due to the resistor R SSIts resistance value is much larger than that of resistor R10. Therefore, the discharge time T2 is calculated using formula (2):

[0103]

[0104] In formula (2), the RC discharge follows an exponential formula, and V ref is the secondary reference voltage, and T2 is the time required to discharge to 0.

[0105] After the system triggers abnormal protection, the soft-start circuit needs to be reset, and this reset process is achieved through the soft-start reset unit. Specifically, the soft-start capacitor C SS discharges through diode D2 to the discharge resistor R10 to achieve the purpose of reset. The time taken for this discharge process is T2. Therefore, T2 also represents the discharge time of the soft-start capacitor C SS and capacitor C V .

[0106] The present invention also includes a control method for the above DC-DC converter control circuit with fast abnormal protection and soft-start smooth self-recovery functions, and this method includes the following steps:

[0107] S1. Abnormal detection

[0108] On the primary side of the DC-DC converter, the first voltage sampling unit consists of an upper voltage-dividing resistor R1 and a lower voltage-dividing resistor R2 to form a voltage-dividing network for sampling the input voltage of the DC-DC converter, and the sampled voltage is sent to the non-inverting input terminal of comparator U1 in the comparator unit. The first reference voltage unit generates a threshold voltage through the current-limiting resistor R3 and the reference source Z1 and inputs it to the inverting input terminal of comparator U1. Comparator U1 compares the sampled voltage with the threshold voltage. When the sampled voltage is lower than the threshold voltage, it is determined as undervoltage and a low-level signal is output. At the same time, the reverse diode D1 in the disabling unit conducts when receiving a low-level effective disabling signal, pulling down the comparison point voltage of comparator U1, causing comparator U1 to output a low-level signal.

[0109] S2. Abnormal protection and status locking maintenance

[0110] The low-level signal output by the comparator U1 activates the maintenance unit and the execution unit to trigger abnormal protection; in the maintenance unit, when the output of comparator U1 is pulled down, the power supply Vcc quickly charges the maintenance capacitor C1, and the maintenance capacitor C1 maintains the protection state according to its charging characteristics, and the duration of maintaining the protection state is T3; in the execution unit, the low-level signal output by comparator U1 causes the switching transistor Q1 to conduct, which in turn drives the switching transistor Q2 to conduct, and finally controls the DC-DC controller to turn off the PWM drive pulse and stop the operation of the DC-DC converter to achieve fast abnormal protection of the DC-DC converter.

[0111] S3. Soft start

[0112] On the secondary side of the DC-DC converter, the second voltage sampling unit consists of an upper voltage-dividing resistor RD1 and a lower voltage-dividing resistor RD2 to form a voltage-dividing network for sampling the output voltage of the DC-DC converter. The sampled voltage is sent to the inverting input terminal of the operational amplifier U2 of the operational amplifier unit. The second reference voltage unit consists of a resistor R11 and a reference source N1. The power supply Vccs provides a working current for the reference source N1 through the resistor R11, and the reference source N1 outputs a stable threshold voltage, which is used as the reference voltage of the operational amplifier U2. In the soft start unit, the power supply charges the capacitor Css through the resistor Rss, causing the reference voltage of the operational amplifier U2 to rise, and the reference voltage is slowly established. This slowly rising reference voltage, in cooperation with the reference voltage provided by the second reference voltage unit, serves as the reference signal for the operational amplifier U2 to control the duty cycle of the driving waveform with different states output by the DC-DC controller to slowly unfold, so as to limit the starting current and ensure the smooth rise of the output voltage.

[0113] S4. Self-reset

[0114] When the system triggers abnormal protection, the secondary output voltage / reference supply voltage drops, that is, the supply voltage of the secondary auxiliary power supply V ccs of the DC-DC converter discharges and drops through the parallel discharge resistor R10. When it drops to a certain proportion, the reverse diode D2 of the soft start reset unit conducts, and the soft start capacitor Css quickly discharges through the diode D2 to the discharge resistor R10 to achieve the reset of the soft start circuit, and the reset time is T2. Ensure that T3 > T2. When the primary side restarts, the secondary can obtain a fully reset soft start loop.

[0115] S5. System restart

[0116] When the input voltage of the DC-DC converter rises and is greater than the turn-on threshold, and at the same time the holding time of the holding unit ends (the voltage drop across the capacitor C1 is not enough to turn on the switch tube), the soft start condition is met. The PWM controller starts to output drive pulses, the DC-DC converter restarts, executes the soft start power-on process, the output voltage is smoothly established, and the system resumes normal operation.

[0117] In order to verify the effectiveness of the control circuit described in the present invention, a comparative analysis is carried out on the traditional design circuit and the control circuit described in the present invention.

[0118] (1) When the input voltage is slowly established, there is a large capacitive load on the secondary side or long-line transmission of the input, etc. Since the input voltage at the DC-DC input drops instantaneously during the start-up process, resulting in under-voltage protection, and then works again in a short time, the example simulation processes of the traditional design circuit and the control circuit described in the present invention are as Figure 9 and Figure 10 shown. InFigure 9 And Figure 10 In [figures] Figure 10 and Figure 9 , the abscissa represents time in ms, and the ordinate represents voltage in V. Figure 9 And Figure 10 are respectively the simulation results of the traditional circuit and the circuit of the present invention under the condition of input voltage oscillation. As Figure 9 shown, when the input voltage oscillation is higher than the undervoltage turn-on voltage again, the converter starts to work immediately. At this time, the internal control circuit has not effectively discharged, and there is abnormal voltage stress on the internal switching tube during the restart process, and the output voltage is established unevenly. As Figure 10 shown, for the control circuit of the present invention, after the input voltage oscillation is higher than the undervoltage turn-on voltage, the DC-DC converter resumes operation only after maintaining the set undervoltage lockout time. The restart process is a soft start, without abnormal voltage stress, and the output establishment process is smooth.

[0119] (2) When the prohibition occurs, due to the jitter of the prohibition signal, the DC-DC controller shuts down instantaneously during the startup process. Since the prohibition unit and the undervoltage protection circuit share the same comparator U1, the protection triggered by the prohibition is similar to the underprotection. Also, in the case of restarting within a short time, the example simulation processes of the traditional circuit and the control circuit of the present invention under the condition of prohibition control level oscillation are as Figure 11 And Figure 12 shown (the low level of the prohibition voltage is valid). As Figure 11 shown, when the prohibition voltage oscillation is higher than the turn-on voltage again, the converter starts to work immediately. At this time, the internal control circuit has not effectively discharged, and there is abnormal voltage stress on the internal switching tube during the restart process, and the output voltage is established unevenly. As Figure 12 shown, when the prohibition level oscillation is higher than the turn-on voltage, the DC-DC converter resumes operation only after maintaining the set prohibition lockout time. The restart process is a soft start, without abnormal voltage stress, and the output establishment process is smooth.

[0120] Specifically, in this embodiment, the function of the prohibition unit is to change the output state of the comparator by pulling down the voltage of the comparator comparison point when receiving a prohibition signal, thereby controlling the action of the protection execution unit to implement the output prohibition function and prevent the circuit from continuing to operate under unsuitable conditions. The under-voltage protection circuit is part of the abnormal protection and state locking and holding circuit, and it mainly consists of a first voltage sampling unit (a voltage division network composed of an upper voltage division resistor R1 and a lower voltage division resistor R2), a comparator unit (including comparator U1), a first reference voltage unit (constituted by a current limiting resistor R3 and a reference source V1), and a protection execution unit, etc. The first voltage sampling unit samples the input voltage of the DC-DC converter and delivers the sampled voltage to the non-inverting input terminal of comparator U1 for comparison with the threshold voltage provided by the first reference voltage unit (connected to the inverting input terminal of comparator U1). When the sampled voltage is lower than the threshold voltage, comparator U1 outputs a low level, triggering the protection execution unit to control the DC-DC controller to turn off the PWM drive pulse to achieve under-voltage protection.

[0121] Under normal circumstances, the under-voltage protection circuit functions. The first voltage sampling unit inputs the sampled voltage to the non-inverting input terminal of comparator U1, and the threshold voltage provided by the first reference voltage unit is input to the inverting input terminal of comparator U1. Comparator U1 outputs a corresponding signal according to the magnitude relationship between these two voltages to determine whether it is in an under-voltage state. When the prohibition unit receives a valid prohibition signal (low level is valid), the reverse diode D1 in the prohibition unit conducts, pulling down the voltage of the comparison point of comparator U1. At this time, it is equivalent to changing the voltage of the non-inverting input terminal of comparator U1, causing the output state of comparator U1 to change, just like when in an under-voltage state, thereby triggering the protection execution unit to act and turn off the PWM drive pulse to achieve output prohibition. Therefore, under different working conditions, the under-voltage protection circuit and the prohibition circuit share comparator U1 to implement their respective functions.

[0122] When the system triggers abnormal protection, the first voltage sampling unit in the abnormal protection and state locking and holding circuit on the primary side will detect the corresponding input or prohibition signal V C1 , and the comparator unit compares this signal with the threshold signal of the first reference voltage unit to generate a protection control signal V p1 . The protection control signal V p1After generation, the protection state maintenance capacitor C1 is quickly charged to Vcc. The switching transistors Q1 and Q2 are turned on, and the execution unit starts to perform the protection action. Due to the effect of the maintenance capacitor C1, the switching transistors Q1 and Q2 remain turned on, and the control circuit is prohibited from sending drive signals until the voltage drop across the capacitor C1 is insufficient to turn on the switching transistors, and then it starts to exit the protection state. The duration of the protection action maintained by the capacitor C1 is denoted as T1. At the same moment when the protection action in the execution state is performed, the secondary output voltage / reference supply voltage of the DC-DC converter starts to drop. The second voltage sampling unit in the soft start and self-reset circuit monitors the change of this signal and feeds it back to the primary side of the DC-DC converter through the operational amplifier unit. At this time, the primary side of the DC-DC converter is still in the protection state, and the PWM controller does not send drive waveforms, so the output continues to drop. When the voltage drops to a certain proportion, the reverse diode D2 in the soft start reset unit starts to conduct, and the reset action starts. The soft start capacitor C SS is reset, and the duration is T2. At this time, as long as appropriate circuit parameters are configured to ensure that T1>T2, when the primary side restarts, a fully reset soft start loop can be obtained on the secondary side of the DC-DC converter. When the abnormal state exits and the DC-DC converter meets the start threshold again, it will perform a soft start and power-on again to resume operation.

[0123] When an abnormal protection occurs in the system, according to the maintenance time of the abnormal protection and state locking and holding circuit and the recovery time required for soft start, a typical protection and recovery action can be divided into the following 4 cases.

[0124] (1) The input voltage of the DC-DC converter is greater than the turn-on threshold, and the duration is greater than t1 (t1 represents the time required for the output to be normally established); then, the input voltage of the DC-DC converter drops below the protection threshold, and the duration is greater than T2 (T2 represents the reset time of the soft start circuit); finally, the input voltage of the DC-DC converter rises above the turn-on threshold, and the DC-DC converter performs a complete soft start, and the secondary circuit is completely reset.

[0125] (2) The input voltage of the DC-DC converter is greater than the turn-on threshold, and the duration is greater than t1. Then, the input voltage of the DC-DC converter drops below the protection threshold, and the duration is less than T2. Finally, the input voltage of the DC-DC converter rises above the turn-on threshold, the DC-DC converter performs a soft start, the output is fully established, and relying on the effect of the maintenance capacitor C1, the PWM drive pulse blocking is forcibly maintained, and the secondary circuit can be completely reset. When working again, the soft start is performed again.

[0126] (3) The input voltage of the DC-DC converter is greater than the turn-on threshold and the duration is less than t1. Then, the input voltage of the DC-DC converter drops below the protection threshold and the duration is greater than T2. Finally, the input voltage of the DC-DC converter rises above the turn-on threshold. The DC-DC converter performs soft start, the output is not fully established, and the secondary circuit is completely reset. When working again, it starts to perform soft start again.

[0127] (4) The input voltage of the DC-DC converter is greater than the turn-on threshold and the duration is less than t1. Then, the input voltage of the DC-DC converter drops below the protection threshold and the duration is less than T2. Finally, the input voltage of the DC-DC converter rises above the turn-on threshold. The DC-DC converter performs soft start, the output is not fully established, and the soft start relies on the function of the maintaining capacitor C1 to forcibly keep the PWM drive pulse blocked to achieve complete reset. When working again, it starts to perform soft start again.

[0128] Regarding the contradiction between the time interval T1 required for the system to restart after triggering abnormal protection and the time T2 required for the complete reset of the secondary soft start circuit, four different situations are analyzed in detail. By reasonably configuring the circuit parameters, it is ensured that the effective reset of the soft start circuit and the smooth establishment of the output voltage can be achieved in various situations. Among them, the minimum maintenance time refers to the minimum time for the maintaining capacitor C1 in the maintaining unit to maintain the protection state. When the system triggers abnormal protection (such as undervoltage or receiving a prohibition signal), the comparator U1 outputs a high level, causing the maintaining capacitor C1 to start charging. As the capacitor C1 charges, the voltage across its two ends rises, the switching transistors Q1 and Q2 conduct, and the execution unit 5 starts to perform the protection action. Due to the energy storage effect of the capacitor C1, this protection state will be maintained for a period of time. This time length is related to the parameters of the capacitor C1 (such as capacitance value) and the resistors connected to it (such as the discharge resistors R5 and R6), etc. The purpose of setting the minimum maintenance time is to ensure that after detecting an abnormality, the protection state can be maintained for a certain period of time to avoid frequent switching of the protection state due to fluctuations in the sampled voltage within a short period of time. This can ensure the stability and reliability of the circuit, prevent the circuit from restarting when the abnormal situation has not been completely resolved, and thus cause damage to the circuit components.

[0129] By reasonably setting the minimum maintenance time and combining it with the reset mechanism of the soft-start circuit, it can ensure that the DC-DC converter has sufficient reset duration under various conditions (such as different input voltage fluctuations, inhibit signal conditions, etc.), thereby improving the reliability of the entire DC-DC converter. For example, when the time interval T1 required for the system to restart (related to the maintenance action duration of capacitor C1) is greater than the time T2 required for the soft-start circuit to be fully reset, when restarting on the primary side, a fully reset soft-start loop can be obtained on the secondary side of the DC-DC converter, thus achieving a smooth restart.

[0130] In summary, through the maintenance capacitor C1, soft-start, and self-reset circuit, regardless of how quickly the input voltage / inhibit signal fluctuates, as long as the minimum maintenance time is set properly, it can ensure that the DC-DC converter has sufficient reset duration and improve the reliability of the DC-DC converter.

[0131] As Figure 13 shown, when the input voltage of the DC-DC converter rises from the undervoltage state to the normal operating voltage state, the PWM controller immediately starts to output drive pulses, and the DC-DC converter restarts. When the soft-start capacitor Css is not fully discharged, the output is prone to jitter.

[0132] As Figure 14 shown, after the input voltage of the DC-DC converter rises from the undervoltage state to the normal operating voltage state, due to the effect of the maintenance capacitor C1, the DC-DC converter is still protected for a period of time, and the PWM controller does not output drive pulses. After experiencing the maintenance time T3, the PWM controller starts to output drive pulses, and the DC-DC converter restarts. At this time, the secondary soft-start circuit is fully reset, and the output is smoothly established.

[0133] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A control circuit for a DC-DC converter with fast overcurrent protection and soft-start smooth self-recovery functions, characterized in that, The control circuit includes an abnormal protection and status locking and holding circuit located on the primary side of the DC-DC converter and a soft start and self-reset circuit located on the secondary side of the DC-DC converter; The abnormal protection and status locking and holding circuit includes a first voltage sampling unit, a first reference voltage unit, a comparator unit, a maintaining unit, an executing unit, and a prohibiting unit; the first voltage sampling unit is used to collect the input voltage of the DC-DC converter; the first reference voltage unit is used to provide a threshold voltage; the comparator unit is used to compare the output voltage of the first voltage sampling unit with the threshold voltage generated by the first reference voltage unit and provide voltage hysteresis control; the executing unit is used to control the DC-DC controller to turn off the PWM drive pulse; the maintaining unit is used to provide additional time protection and control the PWM drive to maintain a non-wave output state; the prohibiting unit is used to pull down the voltage of the comparator comparison point when prohibition occurs to achieve output prohibition; The soft start and self-reset circuit includes a second voltage sampling unit, a soft start unit, a soft start reset unit, a second reference voltage unit, and an operational amplifier unit; the second voltage sampling unit is used to sample the output voltage of the DC-DC converter; the second reference voltage unit is used to provide a threshold voltage as the reference voltage; the soft start unit is used to achieve a slow establishment process of the reference voltage; the operational amplifier unit is used to compare the sampled voltage with the reference voltage and provide stable closed-loop control as an error amplifier; the soft start reset unit is used to provide a fast discharge loop for the capacitor in the soft start unit to achieve the reset of the soft start circuit when the circuit triggers the abnormal protection state.

2. The control circuit of the DC-DC converter with fast abnormal protection and smooth self-recovery function of soft start according to claim 1, characterized in that The first voltage sampling unit adopts a voltage division network, including an upper voltage division resistor R1 and a lower voltage division resistor R2 connected in series; the first end of the upper voltage division resistor R1 is connected to the power supply V in , the second end of the upper voltage division resistor R1 is connected to the first end of the lower voltage division resistor R2, and the second end of the lower voltage division resistor R2 is grounded; The first reference voltage unit includes a current-limiting resistor R3 and a reference source Z1; the first end of the current-limiting resistor R3 is connected to the power supply Vin, the second end of the current-limiting resistor R3 is connected to the first end of the reference source Z1, and the second end of the reference source Z1 is grounded; one end of the current-limiting resistor R3 is connected to the power supply Vin, the other end is connected to the reference source Z1, and the other end of the reference source Z1 is grounded; The comparator unit includes a comparator U1 and a hysteresis resistor R4; the non-inverting input terminal of the comparator U1 is connected to the connection node between the upper voltage-dividing resistor R1 and the lower voltage-dividing resistor R2, and the inverting input terminal of the comparator U1 is connected to the connection node between the current-limiting resistor R3 and the reference source Z1; the output terminal of the comparator U1 is connected to the non-inverting input terminal of the comparator U1 through the hysteresis resistor R4.

3. The control circuit of the DC-DC converter with fast abnormal protection and smooth self-recovery function of soft start according to claim 2, characterized in that The maintenance unit includes a maintenance capacitor C1, a discharge resistor R5, and a discharge resistor R6; a first end of the maintenance capacitor C1 is connected to a power supply V cc ; a second end of the maintenance capacitor C1 is connected to an output end of the comparator unit, that is, connected to an output end of a first comparator U1; a first end of the discharge resistor R5 is connected to the power supply V cc , a second end of the discharge resistor R5 is connected to a first end of the discharge resistor R6, and a second end of the discharge resistor R6 is connected to the output end of the comparator unit, that is, connected to the output end of the first comparator U1.

4. The control circuit of the DC-DC converter with fast abnormal protection and smooth self-recovery function of soft start according to claim 3, characterized in that The execution unit includes a switching transistor Q1, a switching transistor Q2, and a current-limiting resistor R7; the base of the switching transistor Q1 is connected to the node between the discharge resistor R5 and the discharge resistor R6, and the collector of the switching transistor Q1 is connected to the power supply V cc , the emitter of the switching transistor Q1 is connected to the first end of the current-limiting resistor R7, the second end of the current-limiting resistor R7 is connected to the base of the switching transistor Q2, the collector of the switching transistor Q2 is connected to the voltage V comp , and the emitter of the switching transistor Q2 is grounded.

5. The control circuit of the DC-DC converter with fast abnormal protection and soft-start smooth self-recovery function according to claim 4, characterized in that the prohibition unit includes a reverse diode D1; the anode of the reverse diode D1 is connected to the non-inverting input terminal of the comparator U1, and the cathode of the reverse diode D1 outputs an INH prohibition signal.

6. The control circuit of the DC-DC converter with fast abnormal protection and soft-start smooth self-recovery function according to claim 5, characterized in that The second voltage sampling unit uses a voltage division network, including an upper voltage division resistor R connected in series D1 and a lower voltage division resistor R D2 ; the first end of the upper voltage division resistor R D1 is connected to the power supply Vo, the second end of the upper voltage division resistor R D1 is connected to the first end of the lower voltage division resistor R D2 , and the second end of the lower voltage division resistor R D2 is grounded.

7. The control circuit of the DC-DC converter with fast abnormal protection and soft-start smooth self-recovery function according to claim 6, characterized in that the soft-start unit includes a resistor Rss and a capacitor Css; The second reference voltage unit includes a resistor R11 and a reference source N1. The first end of the resistor R11 is connected to the power supply V ccs , the second end of the resistor R11 is connected to the first end of the reference source N1, and the second end of the reference source N1 is grounded; the first end of the resistor Rss is connected to the anode of the diode D2, and the second end of the resistor Rss is connected to the node between the resistor R11 and the reference source N1; the first end of the capacitor Css is connected to the anode of the diode D2, and the second end of the capacitor Css is grounded.

8. The control circuit of the DC-DC converter with fast abnormal protection and soft-start smooth self-recovery function according to claim 7, characterized in that The soft start reset unit includes a discharge resistor R10, a capacitor C v and a diode D2; a first end of the discharge resistor R10 is connected to a first end of the capacitor C v and then connected to a power supply V ccs , a second end of the discharge resistor R10 is connected to a second end of the capacitor C v and then grounded; an anode of the diode D2 is connected to a non-inverting input terminal of the operational amplifier U2, and a cathode of the diode D2 is connected to the power supply V ccs .

9. The control circuit of the DC-DC converter with fast abnormal protection and soft-start smooth self-recovery function according to claim 8, characterized in that The operational amplifier unit includes operational amplifier U2, capacitor C FS , capacitor C HS and resistor R F ; the non-inverting input terminal of the operational amplifier U2 is connected to the anode of the diode D2, the inverting input terminal of the operational amplifier U2 is connected to the node between the resistor R D1 and the resistor R D2 , and the output terminal of the operational amplifier U2 outputs a voltage signal V EA ; the first end of the capacitor C FS is connected to the output terminal of the operational amplifier U2, the second end of the capacitor C FS is connected to the first end of the resistor R F , and the second end of the resistor R F is connected to the inverting output terminal of the operational amplifier U2; the first end of the capacitor C HS is connected to the output terminal of the operational amplifier U2, and the second end of the capacitor C HS is connected to the inverting input terminal of the operational amplifier U2.

10. The control method of the DC-DC converter control circuit with fast abnormal protection and soft start smooth self-recovery function according to any one of claims 1 to 9, characterized in that, This method includes the following steps: S1. Abnormal detection On the primary side, the first voltage sampling unit continuously samples the input voltage of the DC-DC converter and transmits the sampled voltage to the non-inverting input terminal of the comparator U1 in the comparator unit, and the first reference voltage unit outputs a first threshold voltage to the inverting input terminal of the comparator U1; the comparator U1 compares the sampled voltage with the first threshold voltage. If the sampled voltage is lower than the threshold voltage, it is determined to be an undervoltage state, and the comparator U1 outputs a low-level signal; in addition, the reverse diode D1 in the prohibition unit conducts when receiving a low-level effective prohibition signal, pulling down the voltage of the comparison point of the comparator U1, so that the comparator U1 outputs a low-level signal. S2. Abnormal protection and state locking maintenance The low-level signal output by the comparator U1 activates the maintenance unit and the execution unit to trigger abnormal protection; in the maintenance unit, when the output of the comparator U1 is pulled down, the power supply Vcc charges the maintenance capacitor C1, and the maintenance capacitor C1 maintains the protection state according to its charging characteristics, and the duration of maintaining the protection state is T3; in the execution unit, the low-level signal output by the comparator U1 turns on the switching transistor Q1, which in turn drives the switching transistor Q2 to turn on, and finally controls the DC-DC controller to turn off the PWM drive pulse and stop the operation of the DC-DC converter, so as to achieve fast abnormal protection of the DC-DC converter. S3. Soft start On the secondary side, the second voltage sampling unit continuously samples the output voltage of the DC-DC converter and transmits the sampled voltage to the inverting input terminal of the operational amplifier U2 in the operational amplifier unit; the second reference voltage unit outputs a second threshold voltage as the reference voltage of the operational amplifier U2; the soft-start unit charges the capacitor Css through the resistor Rss, causing the reference voltage of the operational amplifier U2 to rise. This reference voltage serves as the reference signal for the operational amplifier U2 to control the DC-DC controller to output a drive waveform with a gradually increasing duty cycle, so as to limit the starting current and make the output voltage rise smoothly. S4. Self-reset After the system triggers abnormal protection, the supply voltage of the secondary auxiliary power supply V ccs of the DC-DC converter discharges and drops through the parallel discharge resistor R10. When it drops to a certain proportion, the reverse diode D2 in the soft start reset unit conducts, and the soft start capacitor Css discharges to the discharge resistor R10 through the diode D2 to reset the soft start circuit. The reset time is T2, where T2 is less than T3; S5. System restart If the input voltage of the DC-DC converter rebounds and is greater than the turn-on threshold, and the hold time of the hold unit ends, the PWM controller starts to output drive pulses, the DC-DC converter restarts, performs a soft-start power-on process, the output voltage is smoothly established, and the system resumes normal operation.

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