A PWM circuit with dynamic turn-off time adjustment

Abstract

The application discloses a PWM circuit with dynamic adjustment of turn-off time, which is characterized in that the circuit comprises a reference voltage unit, a reference current unit, a turn-off control unit, a turn-on control unit and a logic unit; wherein the reference voltage unit and the reference current unit are used for generating reference voltage and reference current respectively, and are connected to the turn-on control unit at the same time, and through processing of the turn-on control unit, compensation operation of turn-on time of a PWM signal is realized; the turn-off control unit is used for generating turn-off time of the PWM signal; the turn-off control unit and the turn-on control unit are connected with the logic unit respectively to realize output of the PWM signal. The application has simple method and ingenious idea, adopts reference voltage and reference current to perform simple time compensation operation, and thus maximum range control of output voltage is realized through the least circuit structure.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more specifically, to a PWM circuit with dynamically adjustable off-time. Background Technology

[0002] With the rapid development of electronic and electrical technologies, electronic products are becoming increasingly prevalent in daily life, and various power supply technologies are also developing rapidly. Integrated circuit modules used for power supply have evolved from initial resistor-capacitor step-down and linear regulators to subsequent switching power supplies. Corresponding circuit units, while achieving the same functional effects, are continuously developing towards smaller size and higher efficiency.

[0003] In the existing technology, DC-to-DC switching power supplies are the most widely used. This circuit structure can use current-mode control or voltage-mode control, and current-mode control has gradually become the mainstream option for switching power supplies due to its excellent control capability over inductor current.

[0004] Generally, switching power supplies can control the power transistor to turn on or off by generating periodic control signals with appropriate duty cycles, thereby stabilizing the power supply's output voltage and current. Among these, the fixed-frequency control method allows the PWM signal to stabilize the output voltage by adjusting the duty cycle within a clock signal of fixed period length.

[0005] However, this control method typically carries the risk of subharmonic oscillations. Background literature: "Design of a DC / DC Slope Compensation Circuit," Xu Xiangzhu et al., *China Integrated Circuits*, July 2011, pp. 31-36, discloses the principle behind the prevalence of subharmonic oscillations in DC / DC sensors. Furthermore, to overcome this oscillation, a more complex slope compensation circuit is needed, which occupies a larger chip area and consumes more power.

[0006] Furthermore, in a power supply circuit operating at a fixed frequency, the minimum turn-off time is also designed to be fixed. This can easily lead to the minimum turn-off time being unable to adapt to changes in the circuit's duty cycle after the circuit's duty cycle reaches its limit, resulting in a contradiction between the minimum turn-off time and the actual turn-off time. Consequently, the output voltage regulation capability of the power supply circuit is also limited.

[0007] To address the above problems, this invention provides a PWM circuit with dynamically adjustable turn-off time. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a PWM circuit with dynamic off-time adjustment. This circuit achieves reasonable adjustment of the off-time through compensation calculations of a reference voltage unit, a reference current unit, and a turn-on control unit. Simultaneously, in conjunction with the turn-off control unit, it controls the on and off states of the power transistors in the voltage converter.

[0009] The present invention adopts the following technical solution.

[0010] This invention relates to a PWM circuit with dynamically adjustable off-time. The circuit includes a reference voltage unit, a reference current unit, a turn-off control unit, a turn-on control unit, and a logic unit. The reference voltage unit and the reference current unit generate a reference voltage and a reference current, respectively, and are simultaneously connected to the turn-on control unit. Through processing by the turn-on control unit, compensation calculations for the PWM signal's on-time are performed. The turn-off control unit generates the PWM signal's off-time. The turn-off control unit and the turn-on control unit are respectively connected to the logic unit to output the PWM signal.

[0011] Preferably, the reference voltage unit includes a first operational amplifier, a first transistor, a second transistor, and first to fourth resistors; wherein: the non-inverting input terminal of the first operational amplifier is connected to the input signal terminal of the voltage converter, the negative input terminal is connected to the drain of the first transistor, and the output terminal is connected to the gate of the first transistor; the source of the first transistor is connected to the power supply voltage, and the first transistor is mirror-connected to the second transistor; the first resistor is connected between the drain of the second transistor and ground; one end of the second resistor is connected to the drain of the first transistor and the negative input terminal of the first operational amplifier, and one end of the third resistor is connected to the output voltage of the voltage converter; the other ends of the second resistor and the other ends of the third resistor are both grounded through the fourth resistor.

[0012] Preferably, the reference voltage generated by the reference voltage unit is In the formula, R1, R2, R3, and R4 are the resistance values ​​of the first, second, third, and fourth resistors, respectively, and V in and V out These are the input voltage and output voltage of the voltage converter, respectively.

[0013] Preferably, the reference current unit includes a second operational amplifier, a third transistor, a fourth transistor, and a fifth resistor; wherein, the non-inverting input terminal of the second operational amplifier is connected to the input voltage, the negative-inverting input terminal is connected to the drain of the third transistor and one end of the fifth resistor, and the output terminal is connected to the gates of the third transistor and the fourth transistor; the source of the third transistor is connected to the power supply voltage, the drain is grounded after passing through the fifth resistor, and is mirror-connected to the fourth transistor.

[0014] Preferably, the reference current generated by the reference current unit is

[0015]

[0016] In the formula, R5 is the resistance value of the fifth resistor.

[0017] Preferably, the shutdown control unit includes an error measurement unit, a current detection unit, and a first comparator; wherein, the error measurement unit is used to measure the error between the feedback voltage and the reference voltage of the voltage converter; the current detection unit is used to collect the current of the power transistor in the voltage converter and generate an intermittent ramp voltage based on the current; the first comparator is connected to the error measurement unit and the current detection unit respectively, and compares the output of the error measurement unit with the magnitude of the ramp voltage to generate a shutdown control signal.

[0018] Preferably, the conduction control unit includes a compensation operational capacitor, a discharge transistor, and a second comparator; wherein, one end of the compensation operational capacitor is connected to the drain of the fourth transistor in the reference current unit, and the other end is grounded; the drain and source of the discharge transistor are connected in parallel across the compensation operational capacitor, and the gate receives the rising edge feedback of the PWM signal; the second comparator receives the upper plate voltage of the compensation operational capacitor and the reference voltage respectively, and generates a conduction control signal after comparison.

[0019] Preferably, the voltage of the upper plate of the compensation operational capacitor is

[0020]

[0021] In the formula, t is the time elapsed after the discharge tube is completely turned off.

[0022] C represents the capacitance value of the compensation operational capacitor.

[0023] Preferably, the compensation for the PWM signal on-time decreases as the duty cycle of the voltage converter increases; and when the off-time of the discharge tube has not reached... When the discharge tube's turn-off time exceeds a certain threshold, the output of the second comparator is high; when the turn-off time of the discharge tube exceeds a certain threshold, the output of the second comparator is high. When the voltage is low, the output of the second comparator is low; where D is the duty cycle of the voltage converter.

[0024] Preferably, the logic unit includes an RS flip-flop and a logic gate circuit; when the ramp voltage is less than the output of the error measurement unit, the output of the first comparator is low, the output of the second comparator is high, and the logic unit outputs a low-level PWM signal to turn off the high-side power transistor; when the output of the second comparator switches to low, the output of the first comparator is high, and the logic unit outputs a high-level PWM signal to turn on the high-side power transistor.

[0025] The beneficial effects of this invention are that, compared with the prior art, the PWM circuit with dynamic off-time adjustment in this invention achieves reasonable adjustment of the off-time through compensation calculations of a reference voltage unit, a reference current unit, and a turn-on control unit. Simultaneously, in conjunction with the turn-off control unit, it controls the on and off states of the power transistor in the voltage converter. This invention is simple in method and ingenious in concept, using a reference voltage and reference current for simple time compensation calculations, thereby achieving maximum control over the output voltage range with minimal circuit structure.

[0026] The beneficial effects of the present invention also include:

[0027] 1. In this invention, the compensation for the conduction time can be adjusted according to the duty cycle of the voltage converter. When the duty cycle is small, this invention maintains the high-side power transistor in the off state for a longer time. Conversely, when the duty cycle is large, such as close to 100%, this invention can maintain the high-side power transistor in the off state for a shorter time. This method achieves dynamic adjustment and reasonable control of the actual turn-off time, resulting in an output voltage that is closer to the input voltage. This invention eliminates the need for additional circuit structures related to the minimum conduction time while still ensuring circuit safety and the accuracy of basic logic, leading to higher accuracy in the output voltage.

[0028] 2. In the method of the present invention, the adjustment of the turn-off time is based on the actual duty cycle of the circuit and the values ​​of multiple resistors and capacitors. Therefore, the turn-off time is easy to adjust and can be easily reused in a variety of different switching power supply circuits to achieve good turn-off time control function.

[0029] 3. This invention eliminates the need for additional slope compensation circuitry to ensure system stability and overcome subharmonic oscillations. Instead, it saves a significant number of circuit components through time compensation, reducing the size of the control circuitry in the chip, saving chip area, and reducing the power consumption of secondary circuits. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the circuit structure of a PWM circuit with dynamic off-time adjustment according to the present invention.

[0031] Figure 2 This is a schematic diagram of the reference voltage unit in a PWM circuit with dynamically adjustable off-time according to the present invention.

[0032] Figure 3 This is a schematic diagram of the reference current unit in a PWM circuit with dynamically adjustable turn-off time according to the present invention.

[0033] Figure 4This is a schematic diagram of the shutdown control unit in a PWM circuit with dynamic shutdown time adjustment according to the present invention.

[0034] Figure 5 This is a timing diagram of the output of the error measurement unit and the ramp voltage in a PWM circuit with dynamic off-time adjustment in this invention.

[0035] Figure 6 This is a schematic diagram of the conduction control unit in a PWM circuit with dynamic off-time adjustment according to the present invention. Detailed Implementation

[0036] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0037] Figure 1 This is a schematic diagram of the circuit structure of a PWM circuit with dynamically adjustable turn-off time according to the present invention. Figure 1 As shown, this invention relates to a PWM circuit with dynamic off-time adjustment. The circuit includes a reference voltage unit, a reference current unit, a turn-off control unit, a turn-on control unit, and a logic unit. The reference voltage unit and the reference current unit generate a reference voltage and a reference current, respectively, and are simultaneously connected to the turn-on control unit. Comparison calculations for the PWM signal's on-time are performed through comparison by the turn-on control unit. The turn-off control unit generates the PWM signal's off-time. The turn-off control unit and the turn-on control unit are respectively connected to the logic unit to control the voltage converter circuit.

[0038] It is understood that the reference voltage unit and reference current unit in this invention can generate adjustable voltage and current based on the magnitude of the input and output voltages of the voltage converter, respectively. After being activated by the control unit, the constant current is converted into a time-varying ramp voltage. This voltage is compared with the adjustable reference voltage to switch the output state of the control unit.

[0039] The turn-on control unit, as the name suggests, can adjust the PWM signal so that the output of the PWM signal flips as the turn-on control unit flips. Thus, when the turn-on control unit flips, it outputs a control signal that enables the high-side power transistor of the voltage converter to switch from the off state to the on state.

[0040] On the other hand, the reference voltage unit in this invention can similarly control the high-side power transistor's off state.

[0041] After passing through the logic unit, the corresponding control capabilities in the turn-on control unit and the turn-off control unit are integrated, thereby realizing the output of the power transistor gate.

[0042] It should be noted that in this invention, the conduction control unit can adjust the conduction time according to the magnitude of the difference between the input voltage and the output voltage, so that the conduction time of the circuit can adapt to the duty cycle requirements of the circuit under various operating conditions.

[0043] Figure 2 This is a schematic diagram of the reference voltage unit in a PWM circuit with dynamically adjustable turn-off time according to the present invention. Figure 2 As shown, preferably, the reference voltage unit includes a first operational amplifier, a first transistor, a second transistor, and first to fourth resistors; wherein: the non-inverting input terminal of the first operational amplifier is connected to the input signal terminal of the voltage converter, the negative input terminal is connected to the drain of the first transistor, and the output terminal is connected to the gate of the first transistor; the source of the first transistor is connected to the power supply voltage, and the first transistor is mirror-connected to the second transistor; the first resistor is connected between the drain of the second transistor and ground; one end of the second resistor is connected to the drain of the first resistor and the negative input terminal of the first operational amplifier, and one end of the third resistor is connected to the output voltage of the voltage converter; the other ends of the second resistor and the other ends of the third resistor are both grounded through the fourth resistor.

[0044] It is understood that the reference voltage unit in this invention can achieve negative feedback connection of the first operational amplifier when the first transistor is turned on. Since the non-inverting input terminal of the first operational amplifier is the input voltage Vin, the voltages at its negative input terminal and output terminal are also determined. One end of the third resistor is connected to the output voltage Vout. Thus, the second and third resistors are connected in parallel, and both output the current generated by the corresponding voltage to ground through the fourth resistor.

[0045] Based on the principle that the voltage at the connection point of the second and third resistors is equal, the current through the second resistor can be obtained by establishing an equation for the voltage drop across the second and third resistors. Since the first and second transistors are in a mirror connection state, the reference voltage can be accurately obtained based on the resistance value of the first resistor.

[0046] Preferably, the reference voltage generated by the reference voltage unit is

[0047]

[0048] In the formula, R1, R2, R3, and R4 are the resistance values ​​of the first, second, third, and fourth resistors, respectively, and V in and V out These are the input voltage and output voltage of the voltage converter, respectively.

[0049] Based on the above derivation process, the present invention can obtain a reference voltage. The magnitude of this reference voltage is closely related to the difference between the input voltage and the output voltage, and can also be adjusted according to the values ​​of multiple resistors.

[0050] Figure 3 This is a schematic diagram of the reference current unit in a PWM circuit with dynamically adjustable turn-off time according to the present invention. Figure 3 As shown, the reference current unit includes a second operational amplifier, a third transistor, a fourth transistor, and a fifth resistor; wherein, the non-inverting input terminal of the second operational amplifier is connected to the input voltage, the negative-inverting input terminal is connected to the drain of the third transistor and one end of the fifth resistor, and the output terminal is connected to the gate of the third transistor and the gate of the fourth transistor; the source of the third transistor is connected to the power supply voltage, the drain is grounded after passing through the fifth resistor, and is mirrored with the fourth transistor.

[0051] It is understood that the connection method of the second operational amplifier, the third transistor, and the fifth voltage in the reference current unit of this invention is similar to that in the reference voltage unit. When the non-inverting input terminal of the second operational amplifier is the input voltage, the fifth resistor can achieve a reasonable current output on the third transistor. At this time, this current can be mirrored to the fourth transistor, thereby realizing the output of the reference current.

[0052] Preferably, the reference current generated by the reference current unit is

[0053]

[0054] In the formula, R5 is the resistance value of the fifth resistor.

[0055] Understandably, the magnitude of the reference current is directly proportional to the input voltage and inversely proportional to the resistance of the fifth resistor.

[0056] Figure 4 This is a schematic diagram of the shutdown control unit in a PWM circuit with dynamic shutdown time adjustment according to the present invention. Figure 4 As shown, preferably, the shutdown control unit includes an error measurement unit, a current detection unit, and a first comparator; wherein, the error measurement unit is used to measure the error between the feedback voltage and the reference voltage of the voltage converter; the current detection unit is used to collect the current of the high-side or low-side power transistor in the voltage converter and generate an intermittent ramp voltage based on the current; the first comparator is connected to the error measurement unit and the current detection unit respectively, and compares the output of the error measurement unit with the magnitude of the ramp voltage to generate a shutdown control signal.

[0057] In this invention, the reference current and reference voltage units only indirectly generate the corresponding turn-on control signals. The logic of this part is relatively complex, so this paper first describes the turn-off control signals.

[0058] In this invention, the turn-off control signal and the turn-on control signal can respectively control the turn-on and turn-off times of the high-side power transistor and the low-side power transistor. Through this control, the turn-on of the high-side power transistor and the low-side power transistor can be accurately controlled, thereby outputting a stable power supply.

[0059] For the shutdown control unit, it actually controls the turn-off time of the high-side power transistor and the turn-on time of the low-side power transistor. When the output of this unit is not interfered with by other modules in the circuit, the falling edge of the unit's signal from high to low will be identified by the back-end logic circuit as the turn-on time of the high-side power transistor.

[0060] Specifically, the error measurement unit can be a corresponding feedback circuit in a voltage converter in the prior art. This measurement unit is capable of measuring the output voltage or a voltage divider of the output voltage and comparing it with a reference voltage. The output is high when the output voltage or its voltage divider is larger, and low otherwise.

[0061] Additionally, the current sensing unit can obtain the current state at the source of the high-side power transistor. When the high-side power transistor is turned on, this state can be multiplied by the ramp voltage to obtain a gradually increasing output voltage. When the high-side power transistor is turned off, the current is zero, and the ramp voltage is no longer output. Thus, this unit can achieve intermittent ramp voltage output.

[0062] It should be noted that the ramp voltage here can be generated by using a buck converter to achieve high-speed sampling of the power transistor current and then converting it. This ramp voltage can be used to compare with the output of the error measurement unit, thereby realizing the power transistor's turn-off control.

[0063] In addition, the first comparator can compare the size between the two, thus providing a reasonable output when the size states of the two are reversed.

[0064] Figure 5 This is a timing diagram of the output of the error measurement unit and the ramp voltage in a PWM circuit with dynamic off-time adjustment according to the present invention. Figure 5 As shown, when the intermittent ramp voltage reaches its peak value, it will be equal to the output of the error measurement unit. Therefore, the state of the shutdown control signal can be flipped at this moment.

[0065] Figure 6 This is a schematic diagram of the conduction control unit in a PWM circuit with dynamically adjustable turn-off time according to the present invention. Figure 6Preferably, the conduction control unit includes a compensation operational capacitor, a discharge transistor, and a second comparator; wherein, one end of the compensation operational capacitor is connected to the drain of the fourth transistor in the reference current unit, and the other end is grounded; the drain and source of the discharge transistor are connected in parallel across the two ends of the compensation operational capacitor, and the gate receives the rising edge feedback of the PWM signal; the second comparator receives the upper plate voltage of the compensation operational capacitor and the reference voltage respectively, and generates a conduction control signal after comparison.

[0066] Understandably, in this part, the turn-on control unit can calculate the reference voltage and reference current to control the turn-off time. The gate of the discharge transistor is controlled by a related signal, which is typically the same as or related to the signal controlling the rising edge of the PWM signal. The specific implementation of this related signal can refer to existing technologies or be implemented using any suitable voltage signal based on the above approach. Therefore, when the PWM signal is on its rising edge and causes the high-side power transistor to turn on, the discharge transistor will also turn on simultaneously, releasing the charge on the capacitor to reduce the capacitor voltage.

[0067] Specifically, the compensation operational capacitor can be continuously charged when the discharge tube is off, and momentarily discharged when the discharge tube is on. Therefore, from the moment the discharge tube is turned off, the voltage on the upper plate of the compensation capacitor will slowly increase.

[0068] Preferably, the voltage of the upper plate of the compensation operational capacitor is

[0069]

[0070] In the formula, t is the time elapsed after the discharge tube is completely turned off, and C is the capacitance value of the compensation operational capacitor.

[0071] As can be seen, the voltage of the upper plate gradually increases with the extension of the off-time. When the voltage of the upper plate rises above the reference voltage, the output of the second comparator will flip.

[0072] Preferably, the compensation for the PWM signal on-time decreases as the duty cycle of the voltage converter increases; and when the off-time of the discharge tube has not reached... When the discharge tube's turn-off time exceeds a certain threshold, the output of the second comparator is high; when the turn-off time of the discharge tube exceeds a certain threshold, the output of the second comparator is high. When the voltage is low, the output of the second comparator is low; where D is the duty cycle of the voltage converter.

[0073] Understandably, substituting the contents of the above formula yields the moment when the reference voltage equals the voltage across the upper plate of the capacitor. Solving for this moment reveals that the duration of this time increases inversely to the duty cycle, and is also related to the values ​​of the resistor and capacitor.

[0074] After this moment, the output signal of the second comparator flips from high to low, enabling the RS flip-flop and subsequent logic gates to achieve reasonable outputs, ensuring the high-side power transistor is turned on and the low-side power transistor is turned off.

[0075] Preferably, the logic unit includes an RS flip-flop and a logic gate circuit; when the ramp voltage is less than the output of the error measurement unit, the output of the first comparator is low, the output of the second comparator is high, and the logic unit outputs a low-level PWM signal to turn off the high-side power transistor; when the output of the second comparator switches to low, the output of the first comparator is high, and the logic unit outputs a high-level PWM signal to turn on the high-side power transistor.

[0076] Understandably, in this circuit, the logic unit can combine the relevant signals of the turn-on control unit and the turn-off control unit, and output reasonable logic signals to the gate control terminals of the high-end and low-end power transistors respectively, thereby realizing the synchronous turn-on and turn-off of the high-end and low-end power transistors.

[0077] The beneficial effects of this invention are that, compared with the prior art, the PWM circuit with dynamic off-time adjustment in this invention achieves reasonable adjustment of the off-time through compensation calculations of a reference voltage unit, a reference current unit, and a turn-on control unit. Simultaneously, in conjunction with the turn-off control unit, it controls the on and off states of the power transistor in the voltage converter. This invention is simple in method and ingenious in concept, using a reference voltage and reference current for simple time compensation calculations, thereby achieving maximum control over the output voltage range with minimal circuit structure.

[0078] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A PWM circuit with dynamically adjustable turn-off time, characterized in that: The circuit includes a reference voltage unit, a reference current unit, a shutdown control unit, a turn-on control unit, and a logic unit; wherein... The reference voltage unit and the reference current unit are used to generate reference voltage and reference current, respectively, and are simultaneously connected to the conduction control unit. Through the processing of the conduction control unit, the compensation calculation for the conduction time of the PWM signal is realized. The reference current unit includes a second operational amplifier, a third transistor, a fourth transistor, and a fifth resistor; wherein, the non-inverting input terminal of the second operational amplifier is connected to the input voltage, the negative-inverting input terminal is connected to the drain of the third transistor and one end of the fifth resistor, and the output terminal is connected to the gates of the third transistor and the fourth transistor; the source of the third transistor is connected to the power supply voltage, the drain is grounded after passing through the fifth resistor, and is mirror-connected to the fourth transistor. The conduction control unit includes a compensation operational capacitor, a discharge transistor, and a second comparator. One end of the compensation operational capacitor is connected to the drain of the fourth transistor in the reference current unit, and the other end is grounded. The drain and source of the discharge transistor are connected in parallel across the compensation operational capacitor, and its gate receives feedback from the rising edge of the PWM signal. The second comparator receives the voltage on the upper plate of the compensation operational capacitor and the reference voltage, respectively, and generates a conduction control signal after comparison. The shutdown control unit is used to generate the shutdown time of the PWM signal; The shutdown control unit and the turn-on control unit are respectively connected to the logic unit to realize the output of the PWM signal.

2. The PWM circuit with dynamically adjustable turn-off time according to claim 1, characterized in that: The reference voltage unit includes a first operational amplifier, a first transistor, a second transistor, and first to fourth resistors; wherein; The non-inverting input terminal of the first operational amplifier is connected to the input signal terminal of the voltage converter, the negative input terminal is connected to the drain of the first transistor, and the output terminal is connected to the gate of the first transistor. The source of the first transistor is connected to the power supply voltage, and the first transistor is mirror-connected to the second transistor; The first resistor is connected between the drain of the second transistor and ground; One end of the second resistor is connected to the drain of the first transistor and the negative input terminal of the first operational amplifier, and one end of the third resistor is connected to the output voltage of the voltage converter. The other end of the second resistor and the other end of the third resistor are both grounded after passing through the fourth resistor.

3. The PWM circuit with dynamically adjustable turn-off time according to claim 2, characterized in that: The reference voltage generated by the reference voltage unit is In the formula, , , and These are the resistance values ​​of the first resistor, the second resistor, the third resistor, and the fourth resistor, respectively. and These are the input voltage and output voltage of the voltage converter, respectively.

4. The PWM circuit with dynamically adjustable turn-off time according to claim 3, characterized in that: The reference current generated by the reference current unit is In the formula, The value of the fifth resistor is given.

5. The PWM circuit with dynamically adjustable turn-off time according to claim 4, characterized in that: The shutdown control unit includes an error measurement unit, a current detection unit, and a first comparator; wherein... The error measurement unit is used to measure the error between the feedback voltage and the reference voltage of the voltage converter. The current detection unit is used to collect the current of the power transistor in the voltage converter and generate an intermittent ramp voltage based on the current. The first comparator is connected to the error measurement unit and the current detection unit respectively, and compares the output of the error measurement unit with the magnitude of the ramp voltage to generate a shutdown control signal.

6. The PWM circuit with dynamically adjustable turn-off time according to claim 5, characterized in that: The voltage of the upper plate of the compensation operational capacitor is In the formula, This refers to the time elapsed after the discharge tube is completely turned off. The capacitance value of the compensation operational capacitor.

7. The PWM circuit with dynamically adjustable turn-off time according to claim 6, characterized in that: The compensation for the PWM signal conduction time decreases as the duty cycle of the voltage converter increases; and, When the turn-off time of the discharge tube has not reached When this occurs, the output of the second comparator is high. When the turn-off time of the discharge tube exceeds When this occurs, the output of the second comparator is low. in, The duty cycle of the voltage converter.

8. The PWM circuit with dynamically adjustable turn-off time according to claim 7, characterized in that: The logic unit includes RS flip-flops and logic gate circuits; When the ramp voltage is less than the output of the error measurement unit, the output of the first comparator is low, the output of the second comparator is high, and the logic unit outputs a low-level PWM signal to turn off the high-side power transistor. When the output of the second comparator switches to a low level, the output of the first comparator is a high level, and the logic unit outputs a high-level PWM signal to turn on the high-side power transistor.

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