CN105811740A - A control circuit capable of reducing the minimum pulse width of a PWM controller, a switching power supply device and a control method - Google Patents

Abstract

The invention discloses a control circuit, a switching power supply device and a control method capable of reducing the minimum pulse width of a PWM (pulse-width modulation) controller, wherein the input end of the control circuit is connected with the output end of the PWM controller, and the control circuit is provided with a filter circuit which is connected with the output end of the PWM controller and is used for filtering rectangular waves output by the output end of the PWM controller; the waveform intercepting circuit is respectively connected with the filter circuit and the output end of the PWM controller, and is matched with the filter circuit to form a functional circuit with forward filtering processing and reverse conduction; and a driving circuit connected with the output end of the functional circuit, amplifying and recovering the waveform output by the output end of the functional circuit, and outputting a rectangular wave with a pulse width smaller than that of the rectangular wave output by the output end of the PWM controller. The invention can reduce the pulse width of the rectangular wave emitted by the PWM controller under the condition of unchanging the period, thereby reducing the duty ratio and achieving the purpose of increasing the minimum voltage regulation range of the power supply.

Description

A control circuit capable of reducing the minimum pulse width of a PWM controller, a switching power supply device and a control method

technical field

The invention relates to a control circuit, a switching power supply device and a control method for enlarging the adjustment range of a switching power supply by reducing the minimum pulse width of a PWM controller

Background technique

A common way to realize a switching power supply is to use a PWM controller to maintain a stable output voltage or current, that is, to maintain a stable output voltage or current by controlling the time ratio between the turn-on and cycle of the corresponding switch tube, that is, the duty cycle, through the PWM controller. Especially between heavy load and light load, the constant voltage or constant current output can be realized by changing the duty cycle.

In theory, the duty cycle range of the PWM controller is any value greater than or equal to 0 and less than 1 (but in actual design, it will not be too close to the above two endpoint values, such as the maximum duty cycle of the PWM controller with dual-terminal output The ratio is not greater than 0.5), so that the full range adjustment from zero output without load to maximum output with full load can be realized. However, the commonly used PWM controllers have an inherent starting point when adjusting the duty cycle, and the actual duty cycle is not adjusted from 0%, which causes the output of the power supply to be unstable when the load is very light. In the field of power supply, especially the field of high-voltage power supply, it brings many disadvantages.

Different from conventional power supplies, the output voltage of high-voltage power supplies is very high, up to hundreds of kilovolts. For example, a 200kV high-voltage power supply using a KA3525 controller can output rated voltage at a duty cycle of 7%-8% when it is no-load. If you want to get a stable voltage of 50KV, you may need a duty cycle of less than 2% in theory, and the narrowest (or called minimum) duty cycle of KA3525 is about 2.4%. At this time, KA3525 will not work and output 3 The range above % changes, which leads to the problem of unstable high-voltage power supply output in this case; as shown in Figure 1, the corresponding driving waveform is the output of the PWM controller. , leading to a sharp rise in the final output voltage, and a lot of overshooting of the output voltage. At this time, no matter how the control parameters of the circuit system are adjusted, the system cannot obtain a stable output voltage.

The fundamental reason why the high-voltage power supply is unstable in the above situation is that the energy of each pulse of the PWM controller is too large. The common practice in the existing circuit control technology is to reduce the voltage of the main circuit, thereby reducing the energy of each pulse, but this This solution greatly increases the complexity of the circuit, and is not suitable for power circuits with high power.

Contents of the invention

In view of the defects in the prior art, the purpose of the present invention is to provide a control circuit capable of reducing the pulse width of the PWM controller, which can reduce the rectangular wave pulse sent by the PWM controller under the condition that the cycle is constant. Wide, and then reduce the duty cycle, so that the duty cycle can be adjusted from 0%, in order to achieve the purpose of increasing the minimum voltage regulation range of the power supply.

In order to achieve the above object, technical scheme of the present invention:

A control circuit capable of reducing the minimum pulse width of a PWM controller, the input end of the aforementioned control circuit is connected with the output end of the PWM controller, and it is characterized in that: the control circuit has

Connected with the output terminal of the aforementioned PWM controller, a filter circuit for filtering the rectangular wave output by the output terminal of the PWM controller, to output a periodic waveform structure in which the slope corresponding to the waveform in the rising time interval and the falling time interval gradually changes;

Connect with the aforementioned filter circuit and the output terminal of the PWM controller respectively, and cooperate with the aforementioned filter circuit to form a waveform interception circuit with forward filter processing and reverse conduction functional circuit, the functional circuit can output the filtered out aforementioned Periodic Waveform Structure Periodic waveform structure of the waveform in the falling time interval;

The drive circuit is connected with the output end of the aforementioned functional circuit, amplifies and recovers the waveform output from the output end of the aforementioned functional circuit, and outputs a rectangular wave with a pulse width smaller than that output by the output end of the PWM controller.

Further, the filter circuit includes but is not limited to an RC filter circuit capable of generating a first sawtooth wave with a rising time interval showing a certain logarithmic function trend distribution and a falling time interval showing a certain exponential function trend distribution in each cycle. And any filter circuit of the LC filter circuit capable of generating the first sawtooth wave with a sinusoidal trend distribution in each cycle.

Preferably, the RC filter circuit or the LC filter circuit adopts a first-order filter circuit.

Further, the waveform interception circuit includes a diode, and the diode is connected in parallel with the resistance element in the first-order RC filter circuit or the inductance element in the first-order LC filter circuit, and forms a A common functional circuit is used to filter out the waveforms in the falling time intervals of the aforementioned first sawtooth waves, and generate a second sawtooth wave that only has a rising time interval with a certain logarithmic function trend distribution in each cycle.

Further, the RC filter circuit adopts an adjustable RC filter circuit; by adjusting at least one electronic component in the aforementioned RC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio; The LC filter circuit adopts an adjustable LC filter circuit; by adjusting at least one electronic component in the aforementioned LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio.

Further, the aforementioned control circuit further includes a protection circuit, one end of the protective circuit is connected to the output end of the aforementioned functional circuit, and the other end of the protection circuit is grounded.

Preferably, the protection circuit includes a TVS tube.

Another object of the present invention is to provide a switching power supply device based on the foregoing control circuit, the foregoing device comprising:

A control circuit with any one of the aforementioned circuit structures.

Another object of the present invention is to provide a kind of control method that can reduce the minimum pulse width of PWM controller, it is characterized in that: comprise the following steps

S1. Filter the rectangular wave output by the output terminal of the PWM controller through the filter circuit to generate the first periodic waveform whose slope corresponding to the waveform in the rising time interval and the falling time interval gradually changes. The aforementioned filtering circuit and the PWM controller The output is connected;

S2, filter out the waveforms in the falling time intervals of the aforementioned periodic waveform structures by the waveform intercepting circuit, generate the second periodic waveform that is filtered out of the waveforms in the falling time interval of the aforementioned first periodic waveform, the aforementioned shape intercepting circuits are respectively connected with the aforementioned The filter circuit is connected to the output terminal of the PWM controller and cooperates with the aforementioned filter circuit to form a functional circuit with forward filter processing and reverse conduction;

S3. Amplify and restore the aforementioned second periodic waveform, and generate a rectangular wave with a pulse width smaller than the pulse width of the rectangular wave output by the output terminal of the PWM controller.

Further, the filter circuit includes but is not limited to an RC filter circuit capable of generating a first sawtooth wave with a rising time interval showing a certain logarithmic function trend distribution and a falling time interval showing a certain exponential function trend distribution in each cycle. And any filter circuit of the LC filter circuit capable of generating the first sawtooth wave with a sinusoidal trend distribution in each period.

Preferably, the RC filter circuit or the LC filter circuit adopts a first-order filter circuit.

Further, the waveform interception circuit includes a diode, and the diode is connected in parallel with the resistance element in the first-order RC filter circuit or the inductance element in the first-order LC filter circuit, and forms a A common functional circuit is used to filter out the waveforms in the falling time intervals of the aforementioned first sawtooth waves, and generate a second sawtooth wave that only has a rising time interval with a certain logarithmic function trend distribution in each cycle.

Further, the RC filter circuit adopts an adjustable RC filter circuit; by adjusting at least one electronic component in the aforementioned RC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio; The LC filter circuit adopts an adjustable LC filter circuit; by adjusting at least one electronic component in the aforementioned LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio.

Compared with prior art, the beneficial effect of the present invention:

The present invention sets a method that can reduce the pulse width of the rectangular wave output by the PWM controller under the condition that the period of the rectangular wave output by the PWM controller remains unchanged, thereby reducing its duty ratio, thereby realizing the duty ratio by using simple circuit elements. The ratio is adjusted from 0% to achieve the purpose of increasing the minimum voltage regulation range of the power supply, and the invention can realize stable control of the high-voltage power supply when it is no-load, greatly expanding the application field of the high-voltage power supply.

Description of drawings

Fig. 1 is the waveform schematic diagram under no-load low voltage of KA3525 controller in the prior art;

Fig. 2 is the circuit connection schematic diagram of control circuit of the present invention;

Figure 3a and Figure 3b are schematic diagrams of the principle of pulse signal duty cycle;

Fig. 4 is the specific circuit schematic diagram that the control circuit of the present invention possesses the RC filtering circuit of first-order form;

Fig. 5 is the specific circuit schematic diagram that the control circuit of the present invention has the LC filtering circuit of first-order form;

Figures 6.1, 6.2, 6.3, 6.4, and 6.5 are waveform diagrams of various stages corresponding to Embodiment 1 of the present invention.

In the figure: 1. PWM controller U, 2. Resistor R or inductor L, 3. Capacitor C, 4. Diode D, 5. Driver M, 6. TVS tube.

detailed description

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.

Combined with Figure 3a, Figure 3b and the concept of duty ratio (duty ratio refers to the ratio of the power-on time (pulse width t) of the pulse signal to the power-on period (period T)), it can be seen that if the period is constant, the reduction A small pulse width can effectively reduce the duty cycle.

Based on the design ideas above, as shown in Figure 2, the present invention designs a control circuit capable of reducing the minimum pulse width of the PWM controller. The aforementioned control circuit filters, intercepts, and then The amplification process subtracts a fixed value from the rectangular wave pulse width output by the output terminal of the PWM controller, so as to achieve the purpose of reducing the duty cycle by a fixed difference (for example: the initial duty cycle of P is 2%-48%, after After the aforementioned control circuit is processed, it becomes 0%-46%, and the fixed value is reduced by 2%),

The input terminal of the aforementioned control circuit is connected to the output terminal of the PWM controller, and the pulse width corresponding to the rectangular wave at the output terminal of the PWM controller is set to be _t1 and the period T, and the control circuit has:

(1), filter circuit, it is connected with aforementioned PWM controller output end, the rectangular wave outputted by PWM controller output end is filtered and processed to output the slope corresponding to the waveform in the rising time interval and the falling time interval to gradually change (increase or reduced) first periodic waveform; the filter circuit includes but is not limited to any circuit structure in an RC filter circuit or an LC filter circuit. Preferably adopt the RC filtering circuit of the first-order form or the LC filtering circuit of the first-order form; Through the filtering process, change the waveform rising time interval or the slope of the falling time interval of the rectangular wave output by the output terminal of the PWM controller, so that the output of the filtering circuit The voltage waveform changes from a rectangular wave to a periodic waveform structure in which the slope of the rising time interval and the falling time interval gradually change. If a first-order RC filter circuit is used, the voltage waveform changes from a rectangular wave to a rise in each cycle. The time interval shows a certain logarithmic function trend distribution, and the falling time interval shows a certain exponential function trend distribution. The first sawtooth wave with a peaked wave shape; if the first-order LC filter circuit is used, the voltage waveform changes from a rectangular wave to a Each cycle has a first sawtooth wave in the shape of a sine wave.

(2), waveform intercepting circuit, it is connected with aforementioned filtering circuit, described PWM controller output end respectively, and cooperates with aforementioned filtering circuit to form the functional circuit with forward filter processing, reverse conducting; aforementioned waveform intercepting circuit Adopt diode, described diode is connected in parallel with the resistance element in the aforementioned first-order RC filter circuit or the inductance element of first-order LC filter circuit, and constitutes the functional circuit with forward filter processing, reverse conduction; The effect of described functional circuit The purpose is to make the current output by the output terminal of the PWM controller flow out. There are only two possibilities: to pass through the filter circuit for filtering processing in the forward direction, and to pass through the waveform interception circuit in the reverse direction, so as to reduce the first sawtooth wave output by the filter circuit. Time interval waveform filtering, if the first-order RC filter circuit is still used, and the aforementioned waveform interception circuit uses a diode, then the voltage waveform becomes a second sawtooth wave that only exists in the rising time interval and is a logarithmic function. The width still maintains the original width t ₁ , and the period is still T.

(3) The drive circuit is connected to the output terminal of the aforementioned functional circuit, amplifies and recovers the waveform output by the output terminal of the aforementioned functional circuit, and generates a rectangular wave whose pulse width is smaller than the rectangular wave pulse width output by the output terminal of the PWM controller . The aforementioned drive circuit adopts a drive amplifier, and there is a jump voltage u in the drive amplifier. When the input voltage is higher than the jump voltage u, it is the maximum output (high level). When the input voltage is less than the jump voltage u, Then it is zero output (low level); so that the aforementioned second sawtooth wave rising time interval waveform is amplified into a high level, and the falling time interval waveform is pulled back to a low level, and the recovery period is still T, and the pulse width is t ₂ , and t ₂ <t ₁ , so t ₂ /T<t ₁ /T, so the duty cycle is reduced.

(4) Since the PWM controller will impact the circuit and generate clutter during the turn-on and turn-off process, it is necessary to add a protection circuit that acts as a protection circuit in the circuit. One end of the protection circuit is connected to the output of the aforementioned functional circuit One end is connected, the other end is grounded. Preferably, the protection circuit includes a transient voltage suppressor, that is, a TVS (TransientVoltageSuppresser) tube.

Further, in order to meet the needs of multiple types of PWM controllers with different starting points, each electronic component in the filter circuit can use adjustable components, that is, the RC filter circuit uses an adjustable RC filter circuit; the electronic components in the LC filter circuit Adjustable LC filter circuit is adopted; by adjusting at least one electronic component in the aforementioned RC filter circuit or LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio; The filter circuit is taken as an example to illustrate, by changing the value of the resistor R and or capacitor C, the slope of the second sawtooth wave rise time interval is changed, and at the same time, because the jump voltage u of the drive circuit is constant, the second sawtooth wave is amplified It will also change accordingly, so that the pulse width t ₃ of the rectangular wave output by the drive circuit, t ₃ /T<t ₂ /T,, adjust the t ₃ time, you can adjust the duty ratio t ₃ /T<t ₂ / T.

Another object of the present invention is to provide a switching power supply device based on the foregoing control circuit, the foregoing device comprising:

A control circuit of any one of the aforementioned circuit structures; the input end of the aforementioned control circuit is connected to the output end of the PWM controller; the output end of the driving circuit is connected to the transformer of the switching power supply device.

The following takes the RC filter circuit as an example to describe the above scheme in detail:

The circuit composition shown in Figure 4, the control circuit has: a first-order RC filter circuit, a diode D4 connected in parallel with the resistor R2 in the first-order RC filter circuit to form a functional circuit, a driver M5 and a TVS tube 6; The first-order RC filter circuit includes a resistor R2 and a capacitor C3; the PWM controller 1 rectangular wave output pin is connected to the resistor R2, the other end of the resistor R2 is connected to the capacitor C3, and the other end of the capacitor C3 is grounded. wave, it will be smoothed by the RC circuit; at the same time, the diode D4 is connected in parallel with the resistor R2, and the negative terminal of the diode D4 is connected to the output terminal of the rectangular wave; take a point A between the resistor R2 and the capacitor C3 as the output terminal of the functional circuit , the driver M5 is connected at point A, and the other end of the driver M5 is used as an output; and the TVS tube 6 is connected at point A, and the other end of the TVS tube is grounded for protection. Meanwhile, as shown in FIG. 5 , the principle of the LC filter circuit with the first-order form of the control circuit of the present invention is similar to the principle of the RC filter circuit with the first-order form, and will not be repeated here.

The specific principle is:

1) The PWM controller U sends a rectangular wave according to the needs of the system. The pulse width time is t ₁ , and the single period is T, so the duty ratio is t ₁ /T. (As shown in Figure 6.1, for example, if the duty cycle is between 2% and 48%, in a cycle T, a single pulse width also accounts for 2% to 48% of its cycle)

2) The rectangular wave passes through the first-order RC filter circuit (resistance-capacitance filter circuit), and the rectangular wave is filtered by the resistance-capacitance circuit into a first sawtooth with a peak wave shape with a logarithmic function in the rising time interval and an exponential function in the falling time interval Waves, as shown in Figure 6.2.

3) When the diode D cooperates with the resistor R, when the PWM controller M and the RC filter circuit emit a special-shaped wave, the following phenomenon will occur: when the current flows out, it only passes through the resistor R; when the current flows back, it only passes through the diode D, that is, the diode D and the resistor R can realize The effect of forward filtering and reverse direct conduction, that is, the waveform interception circuit can cut off the falling time interval of the special-shaped wave to form a second sawtooth wave whose rising time interval is a logarithmic function, the period remains unchanged, and the pulse at this time The width is still t ₁ , as shown in Figure 6.3.

4) When the aforementioned second sawtooth wave enters the driver M, there is a jump voltage u in the driver M. When the input voltage is higher than the jump voltage u, the driver M outputs the maximum (high level), and when the input voltage is lower than the jump voltage u When the voltage u is changed, the driver M is zero output (low level); thus, the aforementioned second sawtooth wave rise time interval is amplified to high level, and the fall time interval is pulled back to low level, that is, it becomes a rectangular wave again. However, the pulse width t ₂ of the rectangular wave at this time is obviously smaller than the pulse width t ₁ of the rectangular wave sent by the PWM controller U, but the entire waveform period T has not changed, so the duty cycle is reduced, that is, t ₂ /T< t ₁ /T, as shown in Figure 6.4.

5) By changing the value of the resistor R and the capacitor C, the purpose of reducing the duty cycle by fixed difference is achieved, that is, by changing the slope of the second sawtooth wave rise time interval, since the value of the jump voltage u of the driver M is constant, the aforementioned The amplified part of the second sawtooth wave will also increase or decrease, and finally change the pulse width t ₃ of the square wave of the power driver M, thereby adjusting the duty cycle t ₃ /T<t ₂ /T, as shown in Figure 6.5.

6) Protection circuit: The opening and closing of the PWM controller will impact the circuit and generate clutter, so a TVS tube is connected to the output point A, and the other end of the TVS tube is grounded to protect the circuit.

Another object of the present invention is to provide a kind of control method that can reduce the minimum pulse width of PWM controller, it is characterized in that: comprise the following steps

S1. Filter the rectangular wave output by the output terminal of the PWM controller through the filter circuit to generate the first periodic waveform whose slope corresponding to the waveform in the rising time interval and the falling time interval gradually changes. The aforementioned filtering circuit and the PWM controller The output is connected;

S2, filter out the waveforms in the falling time intervals of the aforementioned periodic waveform structures by the waveform intercepting circuit, generate the second periodic waveform that is filtered out of the waveforms in the falling time interval of the aforementioned first periodic waveform, the aforementioned shape intercepting circuits are respectively connected with the aforementioned The filter circuit is connected to the output terminal of the PWM controller and cooperates with the aforementioned filter circuit to form a functional circuit with forward filter processing and reverse conduction;

S3. Amplify and restore the aforementioned second periodic waveform, and generate a rectangular wave with a pulse width smaller than the pulse width of the rectangular wave output by the output terminal of the PWM controller.

Further, the filter circuit includes but is not limited to an RC filter circuit capable of generating a first sawtooth wave with a rising time interval showing a certain logarithmic function trend distribution and a falling time interval showing a certain exponential function trend distribution in each cycle. And any filter circuit of the LC filter circuit capable of generating the first sawtooth wave with a sinusoidal trend distribution in each period.

Preferably, the RC filter circuit or the LC filter circuit adopts a first-order filter circuit.

Further, the waveform interception circuit includes a diode, and the diode is connected in parallel with the resistance element in the first-order RC filter circuit or the inductance element in the first-order LC filter circuit, and forms a A common functional circuit is used to filter out the waveforms in the falling time intervals of the aforementioned first sawtooth waves, and generate a second sawtooth wave that only has a rising time interval with a certain logarithmic function trend distribution in each cycle.

Further, the RC filter circuit adopts an adjustable RC filter circuit; by adjusting at least one electronic component in the aforementioned RC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio; The LC filter circuit adopts an adjustable LC filter circuit; by adjusting at least one electronic component in the aforementioned LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio.

In summary, the present invention subtracts a fixed value from the rectangular wave pulse width sent by the PWM controller by filtering, intercepting, and re-amplifying, thereby achieving the purpose of reducing the duty cycle by adjusting the difference in the filter circuit. The value of the component can be changed to change the fixed value of the reduced duty cycle. The circuit is simple and reliable, easy to calculate, suitable for a variety of PWM drivers or controllers, and convenient for engineering practice (for example: initial duty cycle 2%-48% , after processing, it becomes 0%-46%, and the fixed value is reduced by 2%), so this control circuit is suitable for full-range duty cycle adjustment, even if the duty cycle is less than 2%, the circuit is still valid, it can be said that the The circuit can eliminate the initial 2% duty cycle starting point of the PWM controller, so as to achieve the purpose of adjusting the duty cycle from 0%.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (10)

1. A control circuit that can reduce the minimum pulse width of the PWM controller, the aforementioned control circuit input terminal is connected with the PWM controller output terminal, it is characterized in that: the control circuit has Connected to the output terminal of the aforementioned PWM controller, a filter circuit that performs filter processing on the rectangular wave output by the output terminal of the PWM controller, so as to output the first periodic waveform in which the slope corresponding to the waveform in the rising time interval and falling time interval gradually changes ; Connect with the aforementioned filter circuit and the output terminal of the PWM controller respectively, and cooperate with the aforementioned filter circuit to form a waveform interception circuit with forward filter processing and reverse conduction functional circuit, the functional circuit can output the filtered out aforementioned a second periodic waveform of the waveform in the falling time interval of the first periodic waveform; Connected to the output terminal of the aforementioned functional circuit, amplifying and recovering the second periodic waveform output by the output terminal of the aforementioned functional circuit and outputting a drive with a rectangular wave whose pulse width is smaller than that of the rectangular wave pulse width output by the output terminal of the PWM controller circuit. 2. The control circuit according to claim 1, characterized in that: The filter circuit includes but is not limited to an RC filter circuit capable of generating a first sawtooth wave with a rising time interval showing a certain logarithmic function trend distribution and a falling time interval showing a certain exponential function trend distribution in each cycle, and an RC filter circuit capable of generating Any filter circuit of the LC filter circuit of the first sawtooth wave with a sine wave trend distribution in each cycle. 3. The control circuit according to claim 2, characterized in that: The RC filter circuit or the LC filter circuit both adopts a first-order filter circuit. 4. The control circuit according to claim 3, characterized in that: The waveform intercepting circuit includes a diode, and the diode is connected in parallel with the resistance element in the first-order RC filter circuit or the inductance element in the first-order LC filter circuit, and has functions of forward filtering and reverse conduction The circuit is used to filter out the waveforms in the falling time intervals of the first sawtooth wave, and generate the second sawtooth wave which only has a certain logarithmic function trend distribution rising time interval in each period. 5. The control circuit according to claim 2, characterized in that: The RC filter circuit adopts an adjustable RC filter circuit; by adjusting at least one electronic component in the aforementioned RC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty cycle; the LC filter circuit The filter circuit adopts an adjustable LC filter circuit; by adjusting at least one electronic component in the aforementioned LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty ratio. 6. The control circuit according to claim 1, characterized in that: The aforementioned control circuit further includes a protection circuit, one end of which is connected to the output end of the aforementioned functional circuit, and the other end of which is grounded. 7. The control circuit according to claim 6, characterized in that: The protection circuit includes a TVS tube. 8. A switching power supply device, characterized in that it comprises the control circuit according to any one of claims 1-7. 9. A control method capable of reducing the minimum pulse width of a PWM controller, characterized in that: comprising the following steps S1. Filter the rectangular wave output by the output terminal of the PWM controller through the filter circuit to generate the first periodic waveform whose slope corresponding to the waveform in the rising time interval and the falling time interval gradually changes. The aforementioned filtering circuit and the PWM controller The output is connected; S2, filter out the waveforms in the falling time intervals of the aforementioned periodic waveform structures by the waveform intercepting circuit, generate the second periodic waveform that is filtered out of the waveforms in the falling time interval of the aforementioned first periodic waveform, the aforementioned shape intercepting circuits are respectively connected with the aforementioned The filter circuit is connected to the output terminal of the PWM controller and cooperates with the aforementioned filter circuit to form a functional circuit with forward filter processing and reverse conduction; S3. Amplify and restore the aforementioned second periodic waveform, and generate a rectangular wave with a pulse width smaller than the pulse width of the rectangular wave output by the output terminal of the PWM controller. 10. The control method according to claim 9, characterized in that: The RC filter circuit adopts an adjustable RC filter circuit; by adjusting at least one electronic component in the aforementioned RC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty cycle; the LC filter circuit The filter circuit adopts an adjustable LC filter circuit; by adjusting at least one electronic component in the aforementioned LC filter circuit, the pulse width of the waveform output by the output terminal of the aforementioned functional circuit is changed to adjust its duty cycle.