CN102307044A - Switching power supply PWM (pulse width modulation) controller with variable frequencies - Google Patents

Abstract

The present invention is applicable to the field of electronic circuits, and provides a frequency-variable switching power supply pulse width modulation controller, including: a sawtooth wave generating circuit, a frequency control circuit and a PWM generator, and the output terminal of the PWM generator is connected to the The input end of the frequency control circuit is connected, the output end of the frequency control circuit is connected with the input end of the sawtooth wave generator, and the output end of the sawtooth wave generator is connected with the input end of the PWM generator. Using the duty cycle value of the pulse width modulation signal as the control signal of its frequency, the DC component of the PWM signal is extracted to control the sawtooth wave generating circuit to realize the change of the oscillation frequency and the change of the frequency of the PWM signal. In this way, the frequency of the pulse width modulation signal can be automatically changed according to the input and output conditions of the switching power supply, and the power conversion efficiency under different working conditions can be optimized. At the same time, the problem of unreliable driving of the pulse transformer when the duty cycle is very large can be solved.

Description

A Pulse Width Modulation Controller of Switching Power Supply with Variable Frequency

technical field

The invention belongs to the field of electronic circuits, in particular to a frequency-variable switching power supply pulse width modulation controller.

Background technique

In switching power supplies, the size of magnetic components is mainly determined by the switching frequency and input and output conditions. For power supplies with a wide range of input or output voltages, the design of the inductance is usually based on unsaturation under the most severe conditions. The output conditions are loose, that is, when the difference between input and output is small, the design margin of the inductor is very large, resulting in an unbalanced state of volume and efficiency. The inductance with better inductance value can be selected by adopting the pulse width modulation control method of switching power supply with switching frequency change, and the power density and power supply efficiency can be improved.

For isolated topologies with wide input and output voltage ranges, such as forward topology, as the input and output voltages change, when the duty ratio is large, the excitation current of the transformer is also large. In order to prevent saturation, the primary inductance of the transformer Both the inductance and the size of the magnetic core need to be large; and when the duty cycle is reduced, the transformer is difficult to saturate with the same inductance and magnetic core size. At this time, the switching frequency can be appropriately reduced to achieve an increase in efficiency.

For non-isolated boost topology, such as BOOST topology, when the output voltage is high and the duty cycle is large, the ripple of the inductor current is also large. In order to meet the requirements of the index, the design of the inductor is often based on the ripple coefficient at this time. For reference, when the output voltage becomes lower and the duty cycle decreases, the inductor current ripple decreases accordingly, but only the same ripple coefficient is required to meet the target requirements, so the switching frequency can be reduced to optimize efficiency.

The same is true for the non-isolated step-down topology, such as the BUCK topology, except that the switching frequency should decrease with the increase of the duty cycle.

Contents of the invention

In order to solve the above-mentioned technical problems, the purpose of the embodiments of the present invention is to provide a frequency-variable switching power supply pulse width modulation controller.

The embodiment of the present invention is achieved in this way, a frequency variable switching power supply pulse width modulation controller, the controller includes:

A sawtooth wave generating circuit whose frequency increases or decreases as the control voltage increases, a frequency control circuit and a PWM generator,

The output end of the PWM generator is connected to the input end of the frequency control circuit, the output end of the frequency control circuit is connected to the input end of the sawtooth wave generator, and the output end of the sawtooth wave generator is connected to the input end of the sawtooth wave generator. connected to the input of the PWM generator.

Further, the controller also includes:

An error amplifier connected to the input of the PWM generator.

Further, the sawtooth wave generating circuit includes:

Timer, capacitor C1003, power supply VCC, resistor R1001, resistor R1002, resistor R1003, capacitor C1001 and PNP transistor Q1001,

The resistor R1001 is connected in series with the resistor R1002, the base of the triode Q1001 is connected to the series connection point of R1001 and R1002, the other end of the resistor R1001 is connected to the frequency control signal 1007, the emitter of Q1001 is connected to the resistor R1002, and the other end of R1002 is connected to a fixed power supply voltage , the collector of Q1001 is connected to capacitor C1001, the high trigger terminal, low trigger terminal and discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of capacitor C1001, the voltage control terminal is connected to the positive terminal of capacitor C1003, clear Zero terminal is connected to supply voltage.

Further, the sawtooth wave generating circuit 1200 includes:

Timer, capacitor C1203, power supply VCC, resistor R1201, resistor R1202, resistor R1203, capacitor C1201 and PNP transistor Q1201,

The resistor R1201 and the resistor R1203 are connected in series, the base of the triode Q1201 is connected to the series connection point of R1201 and R1203, the other end of the resistor R1201 is connected to the timer, the emitter of Q1201 is connected to the resistor R1202, and the other end of R1202 is connected to the frequency control circuit, Q1201 The collector of the timer is connected to the capacitor C1201, the high trigger terminal, the low trigger terminal and the discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of the capacitor C1201, the voltage control terminal is connected to the positive terminal of the capacitor C1203, and the reset terminal Connect to the supply voltage.

Further, the frequency control circuit includes: a resistor R1006, a resistor R1004, a resistor R1005, a capacitor C1002 and an operational amplifier U1001,

The resistor R1006 and the capacitor C1002 form an RC filter circuit to extract the duty cycle value of the PWM signal, and the resistor R1006 is respectively connected to one end of the capacitor C1002 and the non-inverting input end of the operational amplifier U1001, and the other end of the capacitor C1002 is grounded;

Resistor R1004, resistor R1005 and operational amplifier U1001 form a non-inverting amplifier to adjust the frequency control signal, and one end of the resistor R1004 and resistor R1005 is connected to the inverting input terminal of the operational amplifier U1001, and the other end of the resistor R1004 is connected to The output end of the operational amplifier U1001, the other end of the resistor R1005 is grounded.

Further, the error amplifier includes: an operational amplifier 1005 and a peripheral compensation circuit.

Further, the sawtooth wave generating circuit includes: a resistor R301, a resistor R302, a resistor R303, a capacitor C301, a capacitor C302, a transistor Q301, a transistor Q302, a timer, and a power supply VCC for supplying power to the above components,

One end of the resistor R301 is connected to the emitter of the transistor Q301, the other end is connected to one end of the resistor R303, the other end of the resistor R303 is connected to the collector of the transistor Q301, and the base of the transistor Q301 is connected to the base of the transistor Q302 , the collector of the triode Q302 is respectively connected to one end of the capacitor C301 and the timer, and the timer is also connected to the capacitor C302.

Further, the sawtooth wave generating circuit includes: a resistor R501, a resistor R502, a resistor R503, a capacitor C501, a capacitor C502, a transistor Q501, a transistor Q502, a timer, and a power supply VCC for supplying power to the above components,

The emitter of the triode Q501 is connected to the resistor R501, the collector of the triode Q501 is connected to the capacitor C501, the base of the triode Q501 is connected to the base of the triode Q502, and the collector of the triode Q502 is connected to the resistor R503. The emitter of the triode Q502 is connected to one end of the resistor R502, the resistor R502 and the collector of the triode Q501 are both connected to the timer, and the timer is also connected to the capacitor C502.

Further, the sawtooth wave generating circuit includes: capacitor C901, resistor R901, resistor R902, resistor R903, resistor R904, transistor Q901, transistor Q902 and comparator U901,

The emitter of the transistor Q901 is connected to the resistor R901, the collector of the transistor Q901 is connected to the capacitor C901, the base of the transistor Q901 is connected between the resistor R902 and the resistor R903, and the collector of the transistor Q902 is connected to The collector of the transistor Q901 and the emitter of the transistor Q902 are connected to the other end of the capacitor C901, the resistor R902 and the collector of the transistor Q901 are both connected to the timer, and the timer is also connected to the capacitor C902.

In the embodiment of the present invention, the duty cycle value of the pulse width modulation signal is used as the control signal of its frequency, and the DC component of the PWM signal is extracted to represent the size of the duty cycle to control the sawtooth wave generating circuit to realize the change of the oscillation frequency , to achieve the change of PWM signal frequency. In this way, the frequency of the pulse width modulation signal can be automatically changed according to the input and output conditions of the switching power supply, and the power conversion efficiency under different working conditions can be optimized. At the same time, the problem of unreliable driving of the pulse transformer when the duty cycle is very large can be solved.

Description of drawings

Fig. 1 is the control principle of the switching power supply pulse width modulation method with automatic frequency change provided by the embodiment of the present invention;

Fig. 2 is a schematic block diagram of a pulse width modulation control method with an automatically adjustable switching frequency provided by an embodiment of the present invention;

Fig. 3 is a circuit structure diagram of a sawtooth wave generator whose oscillation frequency decreases as the control voltage increases according to the first embodiment of the present invention;

Fig. 4 is the emulation waveform diagram of sawtooth wave generator circuit shown in Fig. 3;

FIG. 5 is a circuit structure diagram of a sawtooth wave generator whose oscillation frequency decreases as the control voltage decreases according to the second embodiment of the present invention;

Fig. 6 is the emulation waveform diagram of sawtooth wave generator circuit shown in Fig. 5;

Fig. 7 is the simplified implementation form of the sawtooth wave generator that the oscillation frequency shown in Fig. 3 decreases as the control voltage increases;

Fig. 8 is a simplified implementation form of the sawtooth wave generator whose oscillation frequency shown in Fig. 5 decreases with the decrease of the control voltage;

Fig. 9 is a schematic diagram of the structure of the sawtooth wave generator provided by the third embodiment of the present invention;

Fig. 10 is a specific realization circuit of the switching power supply pulse width modulation control method in which the switching frequency decreases as the duty ratio increases;

Fig. 11 is an output waveform diagram of the switching power supply pulse width modulation controller described in Fig. 10;

Fig. 12 is the specific implementation circuit of the pulse width modulation method of the switching power supply in which the switching frequency decreases with the decrease of the duty cycle;

FIG. 13 is an output waveform diagram of the pulse width modulation controller of the switching power supply shown in FIG. 12 .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The invention relates to a switching power supply pulse width modulation control method and its implementation, which can automatically change the frequency of the pulse width modulation signal according to the input and output conditions, optimize the power conversion efficiency under different working conditions, and at the same time solve the problem of extremely high duty cycle. The problem of unreliable driving of large pulse transformers. The present invention uses the duty cycle value of the pulse width modulation signal as its frequency control signal, extracts the DC component of the PWM signal, represents the size of the duty cycle, controls the sawtooth wave generating circuit, realizes the change of the oscillation frequency, and reaches the frequency of the PWM signal. Variety.

The invention relates to a pulse width modulation control method with automatic switching frequency adjustment and its implementation. The modified method extracts duty cycle information from the PWM signal output by the controller, and controls the sawtooth wave generator according to the duty cycle to realize increase or decrease in frequency.

Figure 1 shows the control principle of the switching power supply pulse width modulation method with automatic frequency change,

The output end of the PWM generator is connected to the frequency control circuit, the output end of the frequency control circuit is connected to the sawtooth wave generator, and the output end of the sawtooth wave generator is connected to the PWM generator.

The PWM generator outputs the PWM signal, and the frequency control circuit extracts the size of the duty ratio from the PWM signal, and outputs the frequency control signal to the sawtooth wave generating circuit, thereby controlling the sawtooth wave frequency of the sawtooth wave generating circuit, so that the PWM generator outputs The PWM signal frequency changes accordingly.

Fig. 2 shows a schematic block diagram of a pulse width modulation control method whose switching frequency can be automatically adjusted,

201 is a sawtooth wave generator, its frequency can be changed according to the control signal, 202 is an error amplifier, which performs calculations on the error signal of the power supply, and realizes closed-loop stability, and 203 is a PWM generator, which converts the output signal of the error amplifier and the sawtooth wave signal In comparison, a pulse width modulation signal is generated, and the drive circuit 205 controls the switching on and off of the switching tube in the switching power supply. 204 is a schematic diagram of the voltage-frequency control circuit, which generates a control signal of the sawtooth wave generator according to the duty cycle of the PWM signal, so as to realize the increase and decrease of the frequency of the sawtooth wave.

Fig. 3 is the circuit structure of the frequency-variable sawtooth wave generation circuit provided by the first embodiment of the present invention, which utilizes the inherent characteristics of the 555 timer to generate the sawtooth wave.

The sawtooth wave generating circuit includes: resistor R301, resistor R302, resistor R303, capacitor C301, capacitor C302, transistor Q301, transistor Q302, a timer, and a power supply VCC for supplying power to the above components. One end of the resistor R301 is connected to the emitter of the transistor Q301, the other end is connected to one end of the resistor R303, the other end of the resistor R303 is connected to the collector of the transistor Q301, and the base of the transistor Q301 is connected to the base of the transistor Q302 , the collector of the triode Q302 is respectively connected to one end of the capacitor C301 and the timer, and the timer is also connected to the capacitor C302.

In Fig. 3, resistor R301, resistor R302, transistor Q301, transistor Q302 and resistor R303 form a current mirror circuit to charge capacitor C301 with a constant current, so that the terminal voltage of C301, that is, the voltage at 303, increases linearly. 305 is a 555 timer. When the voltage of 303 exceeds the internal threshold of the 555 timer, its internal integrated transistor is turned on, and the charge of C301 is released instantly, so that the voltage of 303 drops to zero, and at the same time, the internal of the 555 timer The triode is turned off, and the current mirror recharges C301, so that a sawtooth wave is generated. The frequency of the sawtooth wave is determined by its voltage rising slope. By changing the voltage of 301, the current of the current mirror can be changed, thereby changing the voltage rising slope of the sawtooth wave. Changes to the sawtooth frequency.

Referring to Fig. 3, as the voltage Vf increases, the voltage of 302 also increases. According to the principle of the current mirror, the voltage of 304 also increases, and the current flowing through the resistor R304 decreases, that is, the charging current of the capacitor C301 decreases, and the charging rate Slow down, the frequency of the sawtooth wave decreases, so that the frequency decreases with the increase of the control voltage.

Please refer to Figure 4, Figure 4 is the simulation waveform of the sawtooth wave generator circuit shown in Figure 3, n_408 is the waveform of 301, n_392 is the waveform of 303, that is, the sawtooth wave output, it can be seen that with the increase of the control voltage Vf, the sawtooth wave The switching frequency is reduced.

Please refer to Figure 5, the frequency of the sawtooth wave increases with the increase of the control voltage. Also, it takes advantage of the inherent characteristics of the 555 timer to generate a sawtooth wave.

The sawtooth wave generating circuit includes: a resistor R501, a resistor R502, a resistor R503, a capacitor C501, a capacitor C502, a transistor Q501, a transistor Q502, a timer, and a power supply VCC for supplying power to the above components,

The emitter of the triode Q501 is connected to the resistor R501, the collector of the triode Q501 is connected to the capacitor C501, the base of the triode Q501 is connected to the base of the triode Q502, and the collector of the triode Q502 is connected to the resistor R503. The emitter of the triode Q502 is connected to one end of the resistor R502, the resistor R502 and the collector of the triode Q501 are both connected to the timer, and the timer is also connected to the capacitor C502.

Among them, resistor R501, resistor R502, transistor Q501, transistor Q502 and resistor R503 form a current mirror circuit, which charges capacitor C501 with a constant current, so that the terminal voltage of C501, that is, the voltage at 503, increases linearly.

Referring to Figure 5, as the voltage Vf increases, the voltage at both ends of the resistor R501 also increases, and the current flowing through the resistor R501 increases, that is, the charging current of the capacitor C501 becomes larger, the charging rate is accelerated, and the frequency of the sawtooth wave increases. Thus, the frequency increases with the increase of the control voltage.

Please refer to the simulation waveform shown in Figure 6, n_487 is the waveform of 501, and n_392 is the waveform of 503, that is, the sawtooth wave output. It can be seen that the switching frequency of the sawtooth wave decreases with the decrease of the control voltage Vf.

FIG. 7 is a simplified implementation form of the sawtooth wave generator shown in FIG. 3 whose oscillation frequency decreases as the control voltage increases.

In this embodiment, the sawtooth wave generating circuit includes: a resistor R701, a resistor R702, a resistor R703, a capacitor C701, a capacitor C702, a transistor Q702, a timer, and a power supply VCC for supplying power to the above components. One end of the resistor R701 is connected to the base of the transistor Q702, the other end is connected to one end of the resistor R703, the other end of the resistor R703 is connected to the base of the transistor Q702, and the collector of the transistor Q702 is respectively connected to one end of the capacitor C701 As well as a timer, the timer is also connected with a capacitor C702. The other end of the capacitor C701 is grounded. The emitter of the transistor Q702 is connected to one end of the resistor R702, and the other end of the R702 is connected to the timer.

In this embodiment, on the basis of the embodiment shown in FIG. 3 , one triode, that is, Q301 is omitted.

FIG. 8 is a simplified implementation of the sawtooth generator shown in FIG. 5 whose oscillation frequency decreases as the control voltage decreases.

In this embodiment, the sawtooth wave generating circuit includes: a resistor R801, a resistor R802, a resistor R803, a capacitor C801, a capacitor C802, a transistor Q801, a timer, and a power supply VCC for supplying power to the above components,

The emitter of the triode Q801 is connected to the resistor R801, the collector of the triode Q801 is connected to the capacitor C801, the base of the triode Q801 is respectively connected to one end of the resistor R802 and the resistor R803, and the collector of the triode Q801 is respectively connected to The capacitor C801 is connected with the timer. The other end of the resistor R802 is connected with a timer. The other end of the resistor R803 is grounded. The timer is also connected with a capacitor C802.

In this embodiment, on the basis of the embodiment shown in FIG. 5 , one transistor is reduced, that is, Q502 in FIG. 5 .

FIG. 9 is another implementation of the sawtooth generator. The sawtooth wave generating circuit includes: a capacitor C901, a resistor R901, a resistor R902, a resistor R903, a resistor R904, a transistor Q901, a transistor Q902 and a comparator U901.

The emitter of the transistor Q901 is connected to the resistor R901, the collector of the transistor Q901 is connected to the capacitor C901, the base of the transistor Q901 is connected between the resistor R902 and the resistor R903, and the collector of the transistor Q902 is connected to The collector of the transistor Q901 and the emitter of the transistor Q902 are connected to the other end of the capacitor C901, the resistor R902 and the collector of the transistor Q901 are both connected to the timer, and the timer is also connected to the capacitor C902.

The switching tube Q902 is controlled by the comparator U901 to discharge the charging capacitor C901 to replace the 555 timer to generate a sawtooth wave. The amplitude of the sawtooth wave is determined by the reference voltage of the inverting input terminal of the comparator U901.

FIG. 10 is a specific implementation of a switching power supply pulse width modulation control method in which the switching frequency decreases as the duty cycle increases.

The sawtooth wave generating circuit 1000 includes: a timer, a capacitor C1003, a power supply VCC, a resistor R1001, a resistor R1002, a resistor R1003, a capacitor C1001 and a PNP transistor Q1001,

The resistor R1001 is connected in series with the resistor R1002, the base of the triode Q1001 is connected to the series connection point of R1001 and R1002, the other end of the resistor R1001 is connected to the frequency control signal 1007, the emitter of Q1001 is connected to the resistor R1002, and the other end of R1002 is connected to a fixed power supply voltage , the collector of Q1001 is connected to capacitor C1001, the high trigger terminal, low trigger terminal and discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of capacitor C1001, the voltage control terminal is connected to the positive terminal of capacitor C1003, clear Zero terminal is connected to supply voltage.

The PWM generator 1001 is composed of a comparator 1003 and peripheral circuits, the error amplifier is composed of an operational amplifier 1005 and a peripheral compensation circuit, and the driving circuit 1002 improves the output capability of the PWM signal. The sawtooth wave generating circuit 1000, the frequency control circuit 1001, the drive circuit 1002, the PWM generator 1003 and the error amplifier 1005 together constitute a switching power supply pulse width modulation controller with automatic frequency change.

The frequency control circuit 1001 includes: a resistor R1006, a resistor R1004, a resistor R1005, a capacitor C1002 and an operational amplifier U1001,

The resistor R1006 and the capacitor C1002 form an RC filter circuit to extract the duty cycle value of the PWM signal, and the resistor R1006 is respectively connected to one end of the capacitor C1002 and the non-inverting input end of the operational amplifier U1001, and the other end of the capacitor C1002 is grounded;

Resistor R1004, resistor R1005 and operational amplifier U1001 form a non-inverting amplifier to adjust the frequency control signal, and one end of the resistor R1004 and resistor R1005 is connected to the inverting input terminal of the operational amplifier U1001, and the other end of the resistor R1004 is connected to The output end of the operational amplifier U1001, the other end of the resistor R1005 is grounded.

In Figure 11, n_392 is the output of the sawtooth generator, which is the waveform of 1004, and n_556 is the PWM output, which is the waveform of 1006.

Please refer to FIG. 12 . FIG. 12 is a specific implementation of the pulse width modulation method of the switching power supply in which the switching frequency decreases as the duty cycle decreases.

In this embodiment, the sawtooth wave generating circuit 1200 includes:

Timer, capacitor C1203, power supply VCC, resistor R1201, resistor R1202, resistor R1203, capacitor C1201 and PNP transistor Q1201.

The resistor R1201 and the resistor R1203 are connected in series, the base of the triode Q1201 is connected to the series connection point of R1201 and R1203, the other end of the resistor R1201 is connected to the timer, the emitter of Q1201 is connected to the resistor R1202, and the other end of R1202 is connected to the frequency control circuit, Q1201 The collector of the timer is connected to the capacitor C1201, the high trigger terminal, the low trigger terminal and the discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of the capacitor C1201, the voltage control terminal is connected to the positive terminal of the capacitor C1203, and the reset terminal Connect to the supply voltage.

The difference between this embodiment and the circuit shown in Fig. 10 is that Fig. 10 shows that the frequency decreases as the duty cycle increases. The circuit shown in Figure 12 shows that the frequency increases with the increase of the duty cycle. It is manifested in the circuit, mainly in that the connection of the triode is different.

In Figure 13, the output of n_392 sawtooth wave generator is the waveform of 1204, and n_556 is the PWM output, which is the waveform of 1206.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (9)

1. A frequency-variable switching power supply pulse width modulation controller, characterized in that the controller comprises: A sawtooth wave generating circuit whose frequency increases or decreases as the control voltage increases, a frequency control circuit and a PWM generator, The output end of the PWM generator is connected to the input end of the frequency control circuit, the output end of the frequency control circuit is connected to the input end of the sawtooth wave generator, and the output end of the sawtooth wave generator is connected to the input end of the sawtooth wave generator. connected to the input of the PWM generator. 2. the variable frequency switching power supply pulse width modulation controller according to claim 1, is characterized in that, described controller also comprises: An error amplifier connected to the input of the PWM generator. 3. The frequency-variable switching power supply pulse width modulation controller according to claim 1, wherein the sawtooth wave generating circuit comprises: Timer, capacitor C1003, power supply VCC, resistor R1001, resistor R1002, resistor R1003, capacitor C1001 and PNP transistor Q1001, The resistor R1001 is connected in series with the resistor R1002, the base of the triode Q1001 is connected to the series connection point of R1001 and R1002, the other end of the resistor R1001 is connected to the frequency control signal 1007, the emitter of Q1001 is connected to the resistor R1002, and the other end of R1002 is connected to a fixed power supply voltage , the collector of Q1001 is connected to capacitor C1001, the high trigger terminal, low trigger terminal and discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of capacitor C1001, the voltage control terminal is connected to the positive terminal of capacitor C1003, clear Zero terminal is connected to supply voltage. 4. The frequency-variable switching power supply pulse width modulation controller according to claim 1, wherein the sawtooth wave generating circuit 1200 comprises: Timer, capacitor C1203, power supply VCC, resistor R1201, resistor R1202, resistor R1203, capacitor C1201 and PNP transistor Q1201, The resistor R1201 and the resistor R1203 are connected in series, the base of the triode Q1201 is connected to the series connection point of R1201 and R1203, the other end of the resistor R1201 is connected to the timer, the emitter of Q1201 is connected to the resistor R1202, and the other end of R1202 is connected to the frequency control circuit, Q1201 The collector of the timer is connected to the capacitor C1201, the high trigger terminal, the low trigger terminal and the discharge terminal of the timer are connected together, and at the same time connected to the positive terminal of the capacitor C1201, the voltage control terminal is connected to the positive terminal of the capacitor C1203, and the reset terminal Connect to the supply voltage. 5. The variable frequency switching power supply pulse width modulation controller according to claim 1, wherein the frequency control circuit comprises: a resistor R1006, a resistor R1004, a resistor R1005, a capacitor C1002 and an operational amplifier U1001, The resistor R1006 and the capacitor C1002 form an RC filter circuit to extract the duty cycle value of the PWM signal, and the resistor R1006 is respectively connected to one end of the capacitor C1002 and the non-inverting input end of the operational amplifier U1001, and the other end of the capacitor C1002 is grounded; Resistor R1004, resistor R1005 and operational amplifier U1001 form a non-inverting amplifier to adjust the frequency control signal, and one end of the resistor R1004 and resistor R1005 is connected to the inverting input terminal of the operational amplifier U1001, and the other end of the resistor R1004 is connected to The output end of the operational amplifier U1001, the other end of the resistor R1005 is grounded. 6 . The frequency-variable switching power supply pulse width modulation controller according to claim 1 , wherein the error amplifier comprises: an operational amplifier 1005 and a peripheral compensation circuit. 7. The variable frequency switching power supply pulse width modulation controller according to claim 1, wherein the sawtooth wave generating circuit comprises: resistor R301, resistor R302, resistor R303, capacitor C301, capacitor C302, transistor Q301 , transistor Q302, timer and power supply VCC for supplying power to the above components, One end of the resistor R301 is connected to the emitter of the transistor Q301, the other end is connected to one end of the resistor R303, the other end of the resistor R303 is connected to the collector of the transistor Q301, and the base of the transistor Q301 is connected to the base of the transistor Q302 , the collector of the triode Q302 is respectively connected to one end of the capacitor C301 and the timer, and the timer is also connected to the capacitor C302. 8. The variable frequency switching power supply pulse width modulation controller according to claim 1, characterized in that, the sawtooth wave generating circuit comprises: resistor R501, resistor R502, resistor R503, capacitor C501, capacitor C502, transistor Q501 , transistor Q502, timer and the power supply VCC for supplying power to the above components, The emitter of the triode Q501 is connected to the resistor R501, the collector of the triode Q501 is connected to the capacitor C501, the base of the triode Q501 is connected to the base of the triode Q502, and the collector of the triode Q502 is connected to the resistor R503. The emitter of the triode Q502 is connected to one end of the resistor R502, the resistor R502 and the collector of the triode Q501 are both connected to the timer, and the timer is also connected to the capacitor C502. 9. The frequency variable switching power supply pulse width modulation controller according to claim 1, characterized in that, the sawtooth wave generating circuit comprises: capacitor C901, resistor R901, resistor R902, resistor R903, resistor R904, transistor Q901 , transistor Q902 and comparator U901, The emitter of the transistor Q901 is connected to the resistor R901, the collector of the transistor Q901 is connected to the capacitor C901, the base of the transistor Q901 is connected between the resistor R902 and the resistor R903, and the collector of the transistor Q902 is connected to The collector of the transistor Q901 and the emitter of the transistor Q902 are connected to the other end of the capacitor C901, the resistor R902 and the collector of the transistor Q901 are both connected to the timer, and the timer is also connected to the capacitor C902.

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