Isolated DC / DC converter and conduction frequency determination method

Abstract

The invention relates to an isolated DC / DC converter and a conduction frequency determination method. The isolated DC / DC converter comprises an input power supply, a transformer, a switching tube, a feedback module, a diode and an energy storage capacitor. The input power supply is used for providing power; the input power supply, the transformer, the switching tube, the diode and the energy storage capacitor form a flyback topological structure; the feedback module is connected with the input end and the control end of the switching tube and used for adjusting the conduction frequency of the switching tube according to the deviation between primary current and feedback voltage, the primary current is current flowing through a primary coil of the transformer when the switching tube is conducted, and the feedback voltage is current flowing through a secondary coil of the transformer when the switching tube is conducted. The feedback voltage is used for reflecting the output voltage of the secondary side of the transformer. Compared with the prior art, an optocoupler and a feedback peripheral circuit device are not needed, a winding coil does not need to be additionally arranged, and the size of the converter is reduced.

Description

Technical Field

[0001] The present application relates to the field of power supply technology, and in particular to an isolated DC / DC converter and a method for determining a conduction frequency. Background Art

[0002] An isolated converter is a type of DC converter that can isolate the power input and output terminals so that when a power failure occurs, the downstream load device or system can be protected.

[0003] In the related art, isolated converters often use optocoupler isolation and magnetic isolation to achieve electrical isolation between the primary and secondary sides. Although relatively easy to implement, the circuit structure is relatively complex and the device size is large, which is not conducive to the miniaturization of the isolated converter. Summary of the Invention

[0004] In order to reduce the size of an isolated converter, the present application provides an isolated DC / DC converter and a method for determining a conduction frequency.

[0005] In a first aspect, the present application provides an isolated DC / DC converter, which adopts the following technical solution: An isolated DC / DC converter includes an input power supply, a transformer, a switch tube, a feedback module, a diode and an energy storage capacitor; The input power supply is used to provide power; The input power supply, the transformer, the switch tube, the diode and the energy storage capacitor form a flyback topology structure; The feedback module is respectively connected to the input end and the control end of the switching tube, and is used to adjust the conduction frequency of the switching tube according to the deviation between the primary current and the feedback voltage. The primary current is the current flowing through the primary coil of the transformer when the switching tube is turned on, and the feedback voltage is used to reflect the output voltage of the secondary side of the transformer.

[0006] By adopting this technical solution, a feedback module is added to the transformer's primary circuit. By detecting the primary current and the feedback voltage reflecting the secondary output voltage, the switching frequency can be adjusted to achieve a stable output. Compared with existing technologies, this solution eliminates the need for an optocoupler, feedback peripheral circuit components, or an additional winding coil, reducing the size of the converter.

[0007] Optionally, the feedback module includes a current sampling unit, a voltage sampling unit and a processing unit; The current sampling unit is connected to the input end of the switch tube, and is used to collect the current flowing through the primary coil of the transformer when the switch tube is turned on, and output a current sampling signal; The voltage sampling unit is used to scan the pulse waveform of the primary side of the transformer when the switch tube is turned off, to convert the pulse waveform into a feedback voltage, and to determine the difference between the feedback voltage and a preset reference voltage, and to output a voltage error signal; The processing unit is connected to the current sampling unit and the voltage sampling unit respectively, and is used to adjust the conduction frequency of the switch tube according to the current sampling signal and the voltage error signal when receiving the current sampling signal and the voltage error signal.

[0008] Optionally, the current sampling unit includes a sampling resistor and a current comparator; One end of the sampling resistor is connected to the input end of the switch tube, and the other end of the sampling resistor is grounded; The non-inverting input terminal of the current comparator is connected to the common terminal of the sampling resistor and the switch tube, the inverting input terminal of the current comparator is grounded, and the current comparator is used to output a current sampling signal.

[0009] Optionally, the voltage sampling unit includes a first voltage dividing resistor, a second voltage dividing resistor and an error amplifier; One end of the first voltage-dividing resistor is connected to the primary coil of the transformer, and the other end is connected to the second voltage-dividing resistor. The free end of the second voltage-dividing resistor is grounded. The common end of the first voltage-dividing resistor and the primary coil of the transformer is used to reflect the pulse waveform of the primary side of the transformer. The common end of the first voltage-dividing resistor and the second voltage-dividing resistor is used to output the feedback voltage. The inverting input terminal of the error amplifier is connected to the common terminal of the first voltage-dividing resistor and the second voltage-dividing resistor, and the non-inverting input terminal is used to access a preset reference voltage. The error amplifier is used to determine the difference between the feedback voltage and the reference voltage and output the voltage error signal.

[0010] Optionally, the processing unit includes an oscillation circuit, a trigger, and a pulse modulation circuit; The oscillation circuit is connected to the error amplifier and is configured to output a clock signal according to the voltage error signal; The pulse modulation circuit is connected to the error amplifier and the current comparator respectively, and is used to output a modulation signal according to the current sampling signal and the voltage error signal; The trigger is connected to the pulse modulation circuit and the oscillation circuit respectively, and is used to output a stable control signal according to the clock signal and the modulation signal, and the control signal is used to control the on and off of the switch tube.

[0011] Optionally, the processing unit further includes an edge detection circuit and an AND gate; The edge detection circuit is connected to the common end of the first voltage-dividing resistor and the second voltage-dividing resistor, and is used to detect the potential of the common end of the primary coil of the transformer and the switching tube, and output a detection signal; The AND gate is connected to the edge detection circuit and the oscillation circuit respectively, and is used to output a trigger signal according to the clock signal and the detection signal; The trigger is connected to the pulse modulation circuit and the AND gate respectively, and is used to output a control signal according to the modulation signal and the trigger signal.

[0012] Optionally, the current sampling unit, the error amplifier and the processing unit are integrated into a chip.

[0013] In a second aspect, the present application provides a method for determining a conduction frequency, which adopts the following technical solution: A method for determining a conduction frequency, applied to the control chip according to the first aspect, the method comprising: Obtaining a load value connected to the secondary side of the transformer; Determine a working mode according to the load value, wherein different working modes are used to match different loads; The conduction frequency is determined according to the operating mode.

[0014] By adopting the above technical solution, the integrated chip can adjust the working mode of the DC converter according to the load to adapt to different loads, so that no load compensation components need to be added to the circuit, and the size of the converter can be further reduced.

[0015] Optionally, the operating mode includes a burst mode, a discontinuous conduction mode, and a boundary conduction mode, and determining the conduction frequency according to the operating mode includes: If the burst mode is selected, the conduction frequency is set to the lowest frequency; If the discontinuous conduction mode is selected, the duration of the low-level signal in each cycle is extended; If the boundary conduction mode is selected, a detection signal is output when it is detected that the potential of the primary coil of the transformer and the common end of the switch tube drops to the power supply voltage.

[0016] In summary, this application includes at least one of the following beneficial technical effects: This application incorporates a feedback module into the transformer's primary circuit. By detecting the primary current and the feedback voltage reflecting the secondary output voltage, the switching frequency can be adjusted to achieve a stable output. Compared to existing technologies, this eliminates the need for an optocoupler, feedback peripheral circuit components, or an additional winding coil, reducing the size of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the principle of an isolated DC / DC converter according to an embodiment of the present application.

[0018] Figure 2 1 is a circuit diagram of an isolated DC / DC converter according to an embodiment of the present application.

[0019] Figure 3 Schematic diagram of the waveform of the primary switch node of the embodiment of the present application.

[0020] Figure 4 It is a schematic diagram of the principle of the oscillation circuit of an embodiment of the present application.

[0021] Figure 5 It is a waveform diagram in the burst mode in an embodiment of the present application.

[0022] Figure 6 This is a waveform diagram in the intermittent mode in the embodiment of the present application.

[0023] Figure 7 It is a waveform diagram under the boundary mode in the embodiment of the present application.

[0024] Figure 8 Schematic diagram of the relationship between load current, inductor current and frequency in three working modes of an embodiment of the present application.

[0025] Figure 9 3 is a flow chart of a method for determining a conduction frequency according to an embodiment of the present application.

[0026] Explanation of the accompanying symbols: 1. Input power supply; 2. Feedback module; 3. Current sampling unit; 4. Voltage sampling unit; 5. Processing unit; 6. Oscillation circuit; 7. Trigger; 8. Pulse modulation circuit; 9. Edge detection circuit. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of this application more clear, the following Figure 1-9 It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0028] The embodiments of the present application disclose an isolated DC / DC converter, which has the advantage of reducing the volume of the isolated converter.

[0029] Reference Figure 1 and Figure 2 The isolated DC / DC converter includes an input power supply 1, a transformer T, a switch tube M1, a feedback module 2, a diode D1 and an energy storage capacitor C1.

[0030] The input power supply 1 is used to provide power. The input power supply 1 can be an independent power supply integrated in an isolated DC / DC converter, and a rechargeable power supply can be selected. The input power supply 1 can also be an external power supply, such as a mains supply. In the embodiment of the present application, the power supply voltage provided by the input power supply 1 is referred to as .

[0031] Furthermore, the input power supply 1, transformer T, switching transistor M1, diode D1, and energy storage capacitor C1 form a flyback topology. Specifically, the same-name terminal of the primary winding of transformer T is connected to the input power supply 1, the opposite-name terminal is connected to the output terminal of switching transistor M1, and the input terminal of switching transistor M1 is grounded. The anode of diode D1 is connected to the opposite-name terminal of the secondary winding of transformer T. Energy storage capacitor C1 is connected in parallel with the secondary winding of transformer T and diode D1. The cathode of diode D1 and the same-name terminal of the secondary winding of transformer T serve as the output terminal of the converter, outputting a stable voltage.

[0032] The flyback topology transfers energy from the primary to the secondary. This energy is stored in the primary magnetic field and transferred to the secondary magnetic field after a certain period of time. Its operating principle is as follows: When switch M is closed, current flows from the input power supply 1 to the primary ground, charging the primary coil and storing energy. At this time, diode D1 is reverse biased, and no current flows in the secondary coil. The load demand is met by energy storage capacitor C1. Conversely, when switch M1 is opened, the primary coil resists the sudden change in current, reversing the coil's polarity and causing diode D1 to forward bias. The energy stored in the primary coil is transferred to the secondary coil and the load through diode D1. At this time, energy storage capacitor C1 replenishes its charge.

[0033] In the embodiment of the present application, the switch tube M1 is an NMOS tube. Of course, in other embodiments, other controllable switch devices can also be selected.

[0034] Furthermore, the feedback module 2 is connected to the input terminal and the control terminal of the switch tube M1, respectively, and is used to adjust the conduction frequency of the switch tube according to the deviation between the primary current and the feedback voltage. Among them, the primary current is the current flowing through the primary coil of the transformer T when the switch tube M1 is turned on, and the feedback voltage is used to reflect the output voltage of the secondary side of the transformer T. By adding the feedback module 2, the present application utilizes the primary side feedback technology for feedback regulation, so that the secondary side of the transformer T can output a stable voltage.

[0035] Specifically, the feedback module 2 includes a current sampling unit 3 , a voltage sampling unit 4 and a processing unit 5 .

[0036] The current sampling unit 3 is connected to the input end of the switch tube M1 and is used to collect the current flowing through the primary coil of the transformer T when the switch tube M1 is turned on, and output a current sampling signal.

[0037] Specifically, the current sampling unit 3 includes a sampling resistor Rc and a current comparator N1. One end of the sampling resistor Rc is connected to the input of the switch M1, and the other end is grounded. The non-inverting input of the current comparator N1 is connected to the common terminal of the sampling resistor Rc and the switch M1, and its inverting input is grounded. The current comparator N1 is used to output a current sampling signal. Of course, in other embodiments, the current sampling unit 3 may also use other instruments, components, or circuits capable of collecting current magnitude.

[0038] The voltage sampling unit 4 is used to scan the pulse waveform of the primary side of the transformer T when the switch tube M1 is turned off, to convert the pulse waveform into a feedback voltage, and to determine the difference between the feedback voltage and a preset reference voltage, and to output a voltage error signal.

[0039] The voltage sampling unit 4 includes a first voltage-dividing resistor Rfb1, a second voltage-dividing resistor Rfb2, an error amplifier N2, and switches M2 and M3. Specifically, one end of the first voltage-dividing resistor Rfb1 is connected to the primary coil of the transformer T, and the other end is connected to the input of the switch M2. The output of the switch M2 is connected to the second voltage-dividing resistor Rfb2. The free end of the second voltage-dividing resistor Rfb2 is grounded. The gate of the switch M2 is connected to the current source. The gate of the switch M3 is connected to the gate of the switch M2. The source of the switch M3 is connected to the input power supply 1. The drain of the switch M3 is connected to the current source. Both the switch M2 and the switch M3 are P-channel MOS transistors. The flyback pulse detection circuit composed of the switch tube M2 and the switch tube M3 can scan the pulse waveform of the primary side of the transformer T when the switch tube M1 is turned off, thereby generating a current IRFB at the common end of the first voltage-dividing resistor Rfb1 and the second voltage-dividing resistor Rfb2 under the joint action of the first voltage-dividing resistor Rfb1. This current IRfb flows through the second voltage-dividing resistor Rfb2 to generate a voltage to ground, that is, the common end of the first voltage-dividing resistor Rfb1 and the second voltage-dividing resistor Rfb2 outputs a feedback voltage. The inverting input terminal of the error amplifier N2 is connected to the common end of the first voltage-dividing resistor Rfb1 and the second voltage-dividing resistor Rfb2, and the non-inverting input terminal is used to connect to a preset reference voltage. The error amplifier N2 is used to determine the difference between the feedback voltage and the reference voltage and output a voltage error signal. In the embodiment of the present application, the voltage error signal output by the error amplifier N2 is presented in the form of a voltage.

[0040] For a typical converter, when the input power supply 1 maintains a stable input voltage, the output voltage on the secondary side of the transformer T is stabilized at a certain amplitude. Therefore, since the common terminal of the first and second voltage-dividing resistors Rfb1 and Rfb2 is used to output the feedback voltage, the voltage output from the common terminal of the first and second voltage-dividing resistors Rfb1 and Rfb2 can be used as an input to the error amplifier N2 and compared with a reference voltage to facilitate feedback regulation when the feedback voltage fluctuates. The reference voltage is the voltage value that the feedback voltage needs to reach, and can be a preset voltage value.

[0041] It can be understood that in the above process, the feedback voltage is obtained from the flyback voltage, and the flyback voltage can reflect the output voltage of the secondary side of the transformer T. Specifically, when the switch tube M1 is closed, the potential of the common end of the first voltage-dividing resistor Rfb1 and the primary coil of the transformer T rises and is higher than The potential of the common terminal of the first voltage dividing resistor Rfb1 and the primary coil of the transformer T is The flyback pulse amplitude between the two diodes is VFLBK = (VOUT + VF + ISEC * ESR) * NPS. Here, VF is the forward bias voltage of the diode, ISEC is the secondary current, ESR is the total impedance of the secondary circuit, and NPS is the conversion ratio between the primary and secondary sides.

[0042] Furthermore, error amplifier N2 only samples the feedback voltage when the secondary current is zero, so ISEC * ESR is zero. Furthermore, because reference voltage VREF = 1V, when the secondary-side output voltage is in a stable output state, the feedback voltage is equal to the reference voltage, 1V. Therefore, based on VFLBK / Rfb1 = VREF / Rfb2, and VREF = 1V, VFLBK = VREF * (Rfb1 / Rfb2), the relationship between the output voltage and the feedback voltage is VOUT = VREF * (Rfb1 / Rfb2) * (1 / NPS) - VF.

[0043] In other embodiments, the voltage sampling unit 4 may use other instruments, components, or circuits capable of collecting voltage to collect the feedback voltage for comparison with the reference voltage.

[0044] The processing unit 5 is connected to the current sampling unit 3 and the voltage sampling unit 4 respectively, and is used to receive the current sampling signal and the voltage error signal, and is used to adjust the conduction frequency of the switch tube according to the current sampling signal and the voltage error signal when the current sampling signal and the voltage error signal are received.

[0045] It is worth noting that in order to ensure stable output of the secondary side of the transformer T, it is necessary to consider not only the voltage fluctuation caused by various factors, but also the impact of the load connected to the secondary side of the transformer T on the output voltage.

[0046] First, it can be understood that when the switch tube M1 is turned on, the primary current increases linearly with a slope of , energy is stored in the primary coil of transformer T1. When the switch tube M1 is turned off, the secondary current decreases linearly with a slope of , energy is transferred from the primary coil to the secondary coil.

[0047] Due to the conservation of inductor energy, the energy added to the primary side is equal to the energy consumed by the secondary side, that is, PIN=PO.

[0048] According to the above content, the primary current for .

[0049] You can also get:

[0050]

[0051]

[0052]

[0053] From the above deduction, we can get that to maintain The output voltage regulation function can be achieved by detecting the load current and adjusting the time T.

[0054] In a specific example, assuming that in the current steady state, the load resistor is R1, the output voltage is Vo1, and the output power is Po1. At this time, the load resistor R1 is changed to the load resistor R2, and the load resistor R2 is greater than the load resistor R1, then the output voltage To reach steady state again, it is necessary to increase the duration of each cycle, that is, to reduce the frequency so that The steady state after adjustment is: the load resistor is R2, the output voltage is Vo2, and the output power is Po2. Among them, the output voltage Vo1 is equal to the output voltage Vo2.

[0055] Based on the above principles, the processing unit 5 is further explained.

[0056] Specifically, the processing unit 5 includes an oscillation circuit 6 , a trigger 7 , a pulse modulation circuit 8 , an edge detection circuit 9 and an AND gate U1 .

[0057] The oscillation circuit 6 is connected to the output terminal of the error amplifier N2 , and is configured to receive the voltage error signal and output a clock signal according to the voltage error signal.

[0058] Reference Figure 3 The edge detection circuit 9 is connected to the common end of the first voltage-dividing resistor Rfb1 and the second voltage-dividing resistor Rfb2, that is, the common end of the first voltage-dividing resistor Rfb1 and the switch tube M2, and is used to detect the potential of the primary coil of the transformer T and the common end of the switch tube and output a detection signal.

[0059] The AND gate U1 is connected to the edge detection circuit 9 and the oscillation circuit 6 respectively, and is used to output a trigger signal.

[0060] The pulse modulation circuit 8 is connected to the error amplifier and the current comparator respectively, and is used to receive the voltage error signal and the current sampling signal, and to output a modulation signal according to the current sampling signal and the voltage error signal.

[0061] The reset terminal of the trigger 7 is connected to the pulse modulation circuit 8, and the set terminal is connected to the output terminal of the AND gate U1, which is used to output a control signal according to the clock signal and the modulation signal. The control signal is used to control the conduction and shutdown of the switch tube.

[0062] Furthermore, the specific working process is: Reference Figure 4 On the one hand, in the oscillation circuit 6, the voltage error signal generates a path after passing through the buffer circuit. The current, and the voltage error signal reflects the difference with There is a linear relationship . Produced The current is added to the fixed current I1 to charge the capacitor C, and the capacitor voltage Comparing with the reference voltage V1 generates a clock signal. The charging process of capacitor C is: .

[0063] It can be understood that the detection signal is a signal that detects whether the secondary inductor current drops to zero at time T in a cycle. When the detection signal is ineffective, the clock signal controls the discharge of capacitor C. At this time, the relationship between the voltage error signal and f is:

[0064] In the above equation, f has a linear relationship with the voltage error signal. Therefore, by amplifying the feedback voltage and comparing it with the reference voltage, a voltage error signal is generated to control the magnitude of the Ibias current, thereby controlling the clock signal and ultimately the oscillator frequency, f. That is, f changes with the voltage error signal.

[0065] On the other hand, when pulse modulation circuit 8 receives the current sampling signal and the voltage error signal, the voltage error signal serves as a peak comparison threshold and is combined with the current sampling signal to generate a modulation signal. The modulation signal and the clock signal pass through trigger 7 to control the on and off of switch M1. In this application, pulse modulation circuit 8 is a PFM current comparator.

[0066] Reference Figure 5-Figure 7 It is worth noting that, in order to adapt to different loads, the isolated DC / DC converter of the embodiment of the present application also provides a variety of operating modes for load regulation. When the load is very light, the minimum frequency is set, and the burst mode is used to shorten the conduction time to allow accurate sampling of the output voltage; when the load becomes heavier, that is, when the secondary inductor current drops to zero at the end of the entire cycle and then maintains it for a period of time before entering the next cycle, it works in discontinuous conduction mode; when the load becomes heavier, the converter works in boundary conduction mode. The boundary conduction mode is a variable frequency, variable peak current mode. When the power switch is turned on, the primary current of the transformer rises until it reaches the internally controlled peak current limit. After the power switch is disconnected, the voltage on the SW pin rises to the output voltage multiplied by the primary to secondary transformer turns ratio plus the input voltage, that is, at this time VSW=VOUT*NPS+ When the secondary current drops to zero through the output diode, the SW pin voltage drops to The boundary mode detector detects this change and turns off the power switch. The boundary conduction mode makes the stimulus current return to zero every cycle.

[0067] Furthermore, when the load changes from light to heavy, burst mode transitions to discontinuous conduction mode. At this point, the load current Iload increases, while the inductor current IL remains unchanged. The output voltage decreases, the voltage differential across the input inductor decreases, and the current IRFB decreases. This reduces the feedback voltage across the first voltage divider resistor Rfb1, and the voltage error signal output by the error amplifier increases. Simultaneously, when transitioning from burst mode to discontinuous conduction mode, the secondary inductor current drops to zero before the end of cycle T. At this point, the detection signal becomes ineffective, and the clock signal assumes direct control. According to the above formula, the increase in frequency f and the increase in the voltage error signal also increase the peak inductor current IPEAK.

[0068] When the load continues to increase, the discontinuous conduction mode transitions to the critical conduction mode. At this time, when the load current Iload continues to increase, the voltage error signal will increase, causing the peak inductor current IPEAK to increase. However, when the discontinuous conduction mode transitions to the critical conduction mode, the secondary inductor current has not yet dropped to zero at time T within a cycle. At this time, the detection signal takes effect, and the detection signal has a higher priority. Before the secondary inductor current has dropped to zero at the end of a complete cycle, that is, before it has dropped to zero, the detection signal makes the secondary inductor current drop to zero. Continue to charge the capacitor C; after the control delay, the secondary inductor current drops to zero, the detection signal flips, and the detection signal causes the capacitor C to discharge; at this point, the oscillator completes one cycle.

[0069] From the above formula, we can see that when the discontinuous conduction mode changes to the critical conduction mode and the load continues to increase, the voltage error signal increases, resulting in It keeps increasing, but the delay is also increasing, and the delay has a greater impact on f in the above formula. When f becomes smaller, the switching loss is reduced and the efficiency is improved.

[0070] Of course, in order to facilitate driving the switch tube M1 to be turned on and off, a driving unit may be further provided on the line connecting the output end of the trigger 7 and the control end of the switch tube M1 .

[0071] In the embodiment of the present application, the current sampling unit 3 , the error amplifier N2 and the processing unit 5 are all integrated into a chip.

[0072] This application incorporates a feedback module 2 into the primary circuit of transformer T. By detecting the primary current and the feedback voltage reflecting the secondary output voltage, the conduction frequency of switch M1 can be adjusted, thereby achieving a stable output. Compared with existing technologies, this eliminates the need for an optocoupler, feedback peripheral circuit components, or an additional winding coil, thus reducing the size of the converter.

[0073] Furthermore, in order to enable the isolated DC / DC converter in the previous embodiment to adapt to different loads, the embodiment of the present application also discloses a conduction frequency determination method, which is applied to the integrated chip in the above-mentioned isolated DC / DC converter to avoid the additional addition of load compensation components, thereby further reducing the size of the converter.

[0074] Reference Figure 8 and Figure 9 , the conduction frequency determination method includes the following steps: Step S100: Acquire the load value connected to the secondary side of the transformer.

[0075] The isolated DC / DC converter is also equipped with a load detection function. The integrated chip can directly obtain the load value connected to the secondary side of the transformer.

[0076] Step S200: determining a working mode according to the load value, wherein different working modes are used to match different loads.

[0077] The operating modes include burst mode, discontinuous conduction mode, and boundary conduction mode. Specifically, when burst mode is selected, the conduction frequency is set to the lowest frequency. When discontinuous conduction mode is selected, the duration of the low-level signal within each cycle is extended. When boundary conduction mode is selected, a detection signal is output when the potential of the common terminal of the transformer primary coil and the switch tube drops to the power supply voltage.

[0078] Since the working principle and working process of each working mode have been explained in the previous embodiment, they will not be repeated here.

[0079] Step S300: Determine the conduction frequency according to the working mode.

[0080] The above are all preferred embodiments of the present application and are not intended to limit the scope of protection of this application. Unless otherwise specified, any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features. In other words, unless otherwise specified, each feature is merely an example of a series of equivalent or similar features.

Claims

1. An isolated DC / DC converter, characterized in that: It includes an input power supply (1), a transformer, a switch tube, a feedback module (2), a diode and an energy storage capacitor; The input power supply (1) is used to provide power; The input power supply (1), the transformer, the switch tube, the diode and the energy storage capacitor form a flyback topology structure; The feedback module (2) is respectively connected to the input terminal and the control terminal of the switching tube, and is used to adjust the conduction frequency of the switching tube according to the deviation between the primary current and the feedback voltage, the primary current being the current flowing through the primary coil of the transformer when the switching tube is turned on, and the feedback voltage being used to reflect the output voltage of the secondary side of the transformer.

2. The isolated DC / DC converter according to claim 1, wherein: The feedback module (2) comprises a current sampling unit (3), a voltage sampling unit (4) and a processing unit (5); The current sampling unit (3) is connected to the input end of the switch tube, and is used to collect the current flowing through the primary coil of the transformer when the switch tube is turned on, and output a current sampling signal; The voltage sampling unit (4) is used to scan the pulse waveform of the primary side of the transformer when the switch tube is turned off, to convert the pulse waveform into a feedback voltage, and to determine the difference between the feedback voltage and a preset reference voltage, and to output a voltage error signal; The processing unit (5) is connected to the current sampling unit (3) and the voltage sampling unit (4) respectively, and is used to adjust the conduction frequency of the switch tube according to the current sampling signal and the voltage error signal when receiving the current sampling signal and the voltage error signal.

3. The isolated DC / DC converter according to claim 2, wherein: The current sampling unit (3) comprises a sampling resistor and a current comparator; One end of the sampling resistor is connected to the input end of the switch tube, and the other end of the sampling resistor is grounded; The non-inverting input terminal of the current comparator is connected to the common terminal of the sampling resistor and the switch tube, the inverting input terminal of the current comparator is grounded, and the current comparator is used to output a current sampling signal.

4. The isolated DC / DC converter according to claim 3, wherein: The voltage sampling unit (4) comprises a first voltage dividing resistor, a second voltage dividing resistor and an error amplifier; One end of the first voltage-dividing resistor is connected to the primary coil of the transformer, and the other end is connected to the second voltage-dividing resistor. The free end of the second voltage-dividing resistor is grounded. The common end of the first voltage-dividing resistor and the primary coil of the transformer is used to reflect the pulse waveform of the primary side of the transformer. The common end of the first voltage-dividing resistor and the second voltage-dividing resistor is used to output the feedback voltage. The inverting input terminal of the error amplifier is connected to the common terminal of the first voltage-dividing resistor and the second voltage-dividing resistor, and the non-inverting input terminal is used to access a preset reference voltage. The error amplifier is used to determine the difference between the feedback voltage and the reference voltage and output the voltage error signal.

5. The isolated DC / DC converter according to claim 4, wherein: The processing unit (5) includes an oscillation circuit (6), a trigger (7) and a pulse modulation circuit (8); The oscillation circuit (6) is connected to the error amplifier and is used to output a clock signal according to the voltage error signal; The pulse modulation circuit (8) is connected to the error amplifier and the current comparator respectively, and is used to output a modulation signal according to the current sampling signal and the voltage error signal; The trigger (7) is connected to the pulse modulation circuit (8) and the oscillation circuit (6) respectively, and is used to output a control signal according to the clock signal and the modulation signal, and the control signal is used to control the on and off of the switch tube.

6. The isolated DC / DC converter according to claim 5, wherein: The processing unit (5) further includes an edge detection circuit (9) and an AND gate; The edge detection circuit (9) is connected to the common end of the first voltage-dividing resistor and the second voltage-dividing resistor, and is used to detect the potential of the primary coil of the transformer and the common end of the switch tube, and output a detection signal; The AND gate is respectively connected to the edge detection circuit (9) and the oscillation circuit (6) and is used to output a trigger signal; The trigger (7) is connected to the pulse modulation circuit (8) and the AND gate according to the clock signal and the detection signal, respectively, and is used to output a control signal according to the modulation signal and the trigger signal.

7. The isolated DC / DC converter according to claim 6, wherein: The current sampling unit (3), the error amplifier and the processing unit (5) are integrated into a chip.

8. A method for determining a conduction frequency, characterized in that: Applied to the chip according to claim 7, the method comprises: Obtaining a load value connected to the secondary side of the transformer; Determine a working mode according to the load value, wherein different working modes are used to match different loads; The conduction frequency is determined according to the operating mode.

9. The method for determining the conduction frequency according to claim 8, wherein: The operating mode includes a burst mode, a discontinuous conduction mode, and a boundary conduction mode, and determining the conduction frequency according to the operating mode includes: If the burst mode is selected, the conduction frequency is set to the lowest frequency; If the discontinuous conduction mode is selected, the duration of the low-level signal in each cycle is extended; If the boundary conduction mode is selected, a detection signal is output when it is detected that the potential of the primary coil of the transformer and the common end of the switch tube drops to the power supply voltage.

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