CN104734474A - Switching power supply and its control circuit and control method - Google Patents

Abstract

The invention provides a switching power supply and a control circuit and a control method thereof. A switching power supply for converting an input voltage to an output voltage, the switching power supply comprising: the power level circuit switches at least one power switch to convert the input voltage into the output voltage according to the driving signal; and a control circuit coupled to the power stage circuit, the control circuit comprising: a Pulse Width Modulation (PWM) circuit for generating a PWM signal according to the feedback signal; and a shaping weighting circuit coupled to the PWM circuit for receiving the PWM signal and delaying a rising edge (rising edge) or falling edge (falling edge) of each period of the PWM signal by a predetermined time according to the input voltage to generate the driving signal.

Description

Switching power supply and its control circuit and control method

technical field

The present invention relates to a switchable power supply and its control circuit and control method, in particular to a switchable power supply for improving total harmonic distortion (Total Harmonic Distortion, THD), its control circuit and control method.

Background technique

FIG. 1A shows a schematic diagram of a typical isolated switching power supply 100 . As shown in FIG. 1A , the voltage Vac to be rectified is, for example, a direct current or alternating current voltage, and is rectified by a rectification circuit 101 to generate an input voltage Vin. The rectification circuit 101 is, for example, a bridge rectification circuit. The isolated power converter circuit 100 utilizes the transformer circuit 102 therein to receive an input voltage Vin and convert it into an output voltage Vout. Wherein, the isolated switching power supply 100 includes the aforementioned transformer circuit 102 , power switch 103 , control circuit 105 , current sensing circuit 106 , and voltage sensing circuit 107 . The control circuit 105 generates the driving signal GATE according to the current sensing signal CS generated by the current sensing circuit 106 and the feedback signal FB generated by the voltage sensing circuit 107 to convert the input voltage Vin into the output voltage Vout. The transformer circuit 102 includes a first winding W1, a second winding W2, and a third winding W3. Wherein, the second winding is coupled to the ground potential, and the first winding W1 and the third winding W3 are jointly coupled to the reference potential, and the voltage sensing circuit 107 senses the output voltage Vout generated by the second winding W2 by the third winding W3 to generate Feedback signal FB.

FIG. 1B shows another schematic diagram of an isolated power converter circuit 200 . Wherein, the control circuit 205 generates the driving signal GATE according to the current sensing signal CS and the feedback signal FB generated by the current sensing circuit 106 to convert the input voltage Vin into the output voltage Vout. However, the difference from the prior art shown in FIG. 1A is that the voltage sensing circuit 207 is coupled to the output end of the second winding W2 of the transformer circuit 202 to directly sense the output voltage Vout, and the optocoupler circuit 204 is used to The result of sensing the output voltage Vout by the voltage sensing circuit 207 is optically converted into a feedback signal FB and input to the control circuit 205 .

The aforementioned typical isolated switching power supplies 100 and 200 have the problem of total harmonic distortion (THD). Switching power supply and its control circuit and control method.

Contents of the invention

The object of the present invention is to overcome the deficiencies and defects of the prior art, and propose a switching power supply and its control circuit and control method for improving total harmonic distortion.

In order to achieve the above purpose, from one point of view, the present invention provides a switching power supply for converting an input voltage into an output voltage, the switching power supply includes: a power stage circuit, according to a driving signal, switch at least one of the power switches to convert the input voltage into an output voltage; and a control circuit, coupled with the power stage circuit, the control circuit includes: a PWM circuit, according to a feedback signal, to generate a PWM signal and a shaping weighting circuit, coupled to the PWM circuit, to receive the PWM signal, and according to the input voltage, the rising edge (rising edge) or falling edge (falling edge) of each cycle of the PWM signal The timing of the occurrence is delayed for a predetermined period of time, and then the driving signal is generated.

To achieve the above purpose, from another point of view, the present invention provides a control circuit of a switching power supply, wherein the switching power supply is used to convert an input voltage into an output voltage, including a power stage circuit, according to a A driving signal, switching at least one of the power switches to convert the input voltage into an output voltage, the control circuit includes: a PWM circuit, according to a feedback signal, to generate a PWM signal; and a shaping weighting circuit, and the PWM The circuit is coupled to receive the PWM signal, and according to the input voltage, in the PWM signal, the rising edge (rising edge) or the falling edge (falling edge) (falling edge) occurrence time point of each cycle is delayed for a preset period of time, Then generate the drive signal.

In a preferred implementation form, the preset time is extended when the input voltage rises, and shortened when the input voltage drops.

In the aforementioned implementation forms, the preset time may be proportional to the input voltage or the variation of the input voltage.

In a preferred implementation form, the power stage circuit includes a transformer circuit.

In a preferred implementation form, the shaping weighting circuit includes: a slope generating circuit for generating a slope, the slope generating circuit receives the PWM signal as a frequency, and the slope generated by the slope generating circuit is related to the reciprocal of the input voltage; and a level comparator, which compares the slope generated by the slope generating circuit with a reference level, and generates the aforementioned driving signal according to the comparison result.

In a preferred implementation form, the shaping weighting circuit includes: a slope generating circuit for generating a slope, the slope generating circuit receives the PWM signal as a frequency; and a level comparator for generating the slope The slope generated by the circuit is compared with the proportional value of the input voltage, and the aforementioned driving signal is generated according to the comparison result.

To achieve the above purpose, from another point of view, the present invention provides a control method of a switching power supply, wherein the switching power supply is used to convert an input voltage into an output voltage, including a power stage circuit, according to a A driving signal, switching at least one of the power switches to convert the input voltage into an output voltage, the control method of the switching power supply includes: generating a PWM signal according to a feedback signal; and receiving the PWM signal, and according to The input voltage delays the rising edge or falling edge of each cycle of the PWM signal for a preset time to generate the driving signal.

In a preferred implementation form, the preset time is extended when the input voltage rises, and shortened when the input voltage drops.

In the aforementioned implementation forms, the preset time may be proportional to the input voltage or the variation of the input voltage.

The following will be described in detail through specific embodiments, so that it is easier to understand the purpose, technical content, characteristics and effects of the present invention.

Description of drawings

FIG. 1A shows a schematic diagram of a typical isolated switching power supply 100;

FIG. 1B shows another schematic diagram of an isolated power converter circuit 200;

2A-2C show a first embodiment of the present invention;

3A-3J show synchronous or asynchronous buck, boost, reverse voltage, buck-boost, and boost reverse power stage circuits;

FIG. 4 shows a schematic diagram of signal waveforms of the input voltage Vin and the delayed preset time Tdelay according to the present invention;

Fig. 5 shows the second embodiment of the present invention;

6A-6C show the third, fourth and fifth embodiments of the present invention.

Description of symbols in the figure

100,200 isolated switching power supply

101 rectifier circuit

102,202 Transformer circuits

103 Power switch

105,205 control circuit

106 Current Sensing Circuit

107 Voltage sensing circuit

204 Optocoupler circuit

300 Switching Mode Power Supply

302 Power stage circuit

303 Power switch

305 control circuit

3051 PWM circuit

3053 Shaping weighting circuit

CS current sense signal

Cs1 charging current source

Cs2 Discharge current source

C1 Capacitance

FB Feedback Signal

I, I1, I2 Current

N1, N2, N3, N4, N5 inverting elements

PWM1 PWM signal

PWM2 driving signal

Q output terminal

Q1,Q2 switch

R reset terminal

S Setting terminal

Tdelay1, Tdelay2 preset time

Vac to be rectified

Vin Input Voltage

Vout output voltage

W1 first winding

W2 Second winding

W3 Third winding

Detailed ways

Referring to Figures 2A-2C, a first embodiment of the present invention is shown. As shown in FIG. 2A , the switch mode power supply 300 includes a power stage circuit 302 and a control circuit 305 . The power stage circuit 302 switches the power switch 303 to convert the input voltage Vin to the output voltage Vout according to a driving signal GATE. The control circuit 305 is coupled to the power stage circuit 302 and includes a pulse width modulation (PWM) circuit 3051 and a shaping weighting circuit 3053 . The PWM circuit 3051 generates a PWM signal PWM1 according to the feedback signal FB. The feedback signal FB is related to the output voltage Vout. For example, it can be obtained from the output terminal of the power stage circuit 302, or from the output voltage Vout, or from the auxiliary winding when the power stage circuit 302 is an isolated power conversion circuit using a transformer. available everywhere. The shaping weighting circuit 3053 is coupled to the PWM circuit 3051 to receive the PWM signal PWM1, and according to the input voltage Vin, in the PWM signal PWM1, when each cycle of rising edge (rising edge) or falling edge (falling edge) occurs point, delay for a predetermined time Tdelay1 or Tdelay2, as shown in FIGS. 2B and 2C , and then generate the driving signal PWM2. As shown in FIGS. 2B and 2C , the PWM circuit 3051 generates a PWM signal PWM1 and inputs it to the shaping weighting circuit 3053 . Referring to FIG. 2B , the shaping weighting circuit 3053 delays the rising edge of each cycle of the PWM signal PWM1 for a preset time Tdelay1 to generate the driving signal PWM2 . Referring to FIG. 2C , the shaping weighting circuit 3053 delays the timing of the falling edge of each period of the PWM signal PWM1 by a preset time Tdelay2 to generate the driving signal PWM2 . Wherein, the power stage circuit 302 can also be a synchronous or asynchronous buck type, boost type, reverse voltage type, or buck-boost type power stage in addition to the isolated switching power supply shown in FIG. 1A and FIG. 1B . The circuit is shown in Figures 3A-3J. As shown in FIGS. 1A and 1B , the isolated switching power supplies 100 and 200 include transformer circuits 102 and 202 .

FIG. 4 shows a schematic diagram of signal waveforms of the input voltage Vin and the delayed preset time Tdelay according to the present invention. As shown in the figure, the preset time Tdelay is extended when the input voltage Vin rises, and shortened when the input voltage Vin drops. A preferred implementation manner is that the preset time Tdelay is set to be proportional to the input voltage Vin, or proportional to the variation ΔVin of the input voltage per unit time (ie, the voltage difference between the current time and the previous time).

Fig. 5 shows a second embodiment of the present invention. This embodiment shows a more specific embodiment of the shaping weighting circuit 3053 . In this embodiment, the shaping weighting circuit 3053 delays, for example but not limited to, the timing of the rising edge of each cycle of the PWM signal PWM1 for a predetermined time Tdelay1 to generate the driving signal PWM2. Figure 5 shows that the shaping weighting circuit 3053 includes inverting elements N1, N2, N3 and N4, switches Q1 and Q2, charging current source Cs1, and capacitor C1, wherein switches Q1 and Q2, charging current source Cs1, and capacitor C1 form a ramp Generating circuit, and the frequency of the ramp generating circuit is determined by the PWM signal PWM1, and the current I of the charging current source Cs1 is proportional to the reciprocal of the input voltage Vin. The purpose of the inverting elements N1 and N2 is to maintain the duty ratio of the PWM signal PWM1 but change the absolute value of its high and low levels to meet the operation requirements of the switches Q1 and Q2. If the level of the PWM signal PWM1 itself is proper, the inverting elements N1 and N2 may not be needed in the circuit. The charging current source circuit Cs1 generates a current I, and the current I is proportional to the reciprocal of the input voltage Vin; the switching of the switches Q1 and Q2 is controlled by the duty ratio of the PWM signal PWM1, and the charging and discharging of the capacitor C1 is controlled by switching the switches Q1 and Q2 , making the voltage of the capacitor C1 (that is, the slope generated by the slope generating circuit) relative to the reciprocal of the input voltage Vin, and then generating the driving signal PWM2 through the inverting elements N3 and N4, so as to produce a delay effect. In detail, since the current I is proportional to the reciprocal of the input voltage Vin, the higher the input voltage Vin is, the smaller the current I is, the slower the charging speed of the capacitor C1 is, and the slower it reaches the level switching point of the inverting element N3. That is, the delay time is proportional to the input voltage Vin. In this embodiment, a comparator can also be used to replace the inverting elements N3 and N4, one end of the comparator receives the voltage of the capacitor C1, and the other end receives a reference voltage (equivalent to the level change point of the inverting element N3); or A smith trigger is used to replace the inverting elements N3 and N4. Inverting elements, comparators, or Smith triggers all have the function of level comparison, and can be regarded as a form of level comparator.

In fact, according to the basic physical formula, the product of capacitance (C) and voltage (V) is equal to the product of current (i) and time (t) (CV=it), so if you want to change the delay time and make the delay time proportional to The input voltage Vin, in addition to changing the current I according to the manner of the embodiment in FIG. 5 , can also change the voltage. FIG. 6A shows a third embodiment of the present invention. This embodiment shows another more specific embodiment of the shaping weighting circuit 3053, which is similar to the second embodiment in FIG. 5, but the current I of the charging current source Cs1 is The shaping weighting circuit 3053 includes a comparator Comp1 to compare the voltage of the capacitor C1 with the relative value Vin/R of the input voltage Vin, where R can be a desired ratio. The correlation value Vin/R can be obtained, for example, from a divided voltage of the input voltage Vin. In this embodiment, the time point when the PWM signal PWM2 changes from the low level to the high level is also delayed by a time proportional to the input voltage Vin compared to the time point when the PWM signal PWM1 changes from the low level to the high level.

The slope generation circuit among Fig. 5 and 6A is the slope generation circuit of rising waveform; 6C shows a slope generating circuit with rising and falling waveforms, wherein Cs2 is a discharge current source. In the embodiment of FIG. 6C, the charging current source Cs1 generates a charging current I1, and the discharging current source Cs2 generates a charging current I2. equal or not equal. When using the ramp generating circuit shown in FIG. 6B or FIG. 6C , the connection mode of the input terminal of the comparator Comp1 can be changed as required.

In addition, obviously, if it is desired to delay the time point when the PWM signal PWM1 changes from a high level to a low level, in the circuit illustrated above, the inverse signal of the PWM signal PWM1 can be used to control the frequency of the ramp generating circuit.

It should be noted that, according to the present invention, total harmonic distortion (Total Harmonic Distortion, THD) and electromagnetic interference (electro-magnetic interference, EMI) can be improved, and has a quasi resonant (quasi resonant, QR) switching power supply device effect. The applicable operation mode of the present invention is preferably applied to the boundary conduction mode (boundary conduction mode, BCM), which is a commonly used technology in this technical field, and will not be described in detail here. Compared with the typical quasi-resonant switching power supply, the circuit of the present invention is simpler and the operation method is simpler, which are the advantages of the present invention over the prior art. Taking a typical quasi-resonant switching power supply as an example, in the prior art, it is necessary to continuously detect the turning point of the high and low levels of the output signal. The circuit and operation method are relatively complicated, and the manufacturing cost is also high.

The present invention has been described above with reference to preferred embodiments, but the above description is only for those skilled in the art to easily understand the content of the present invention, and is not intended to limit the scope of rights of the present invention. Under the same spirit of the present invention, various equivalent changes can be conceived by those skilled in the art. For example, other circuits or components that do not affect main functions may be inserted between two circuits or components that are directly connected as shown in the figures in each embodiment. All of these can be deduced according to the teaching of the present invention, therefore, the scope of the present invention should cover the above and all other equivalent changes.

Claims (15)

1. a switched power supply, in order to input voltage is converted to output voltage, is characterized in that, described switched power supply comprises:

One power stage circuit, according to one drive signal, switch wherein at least one power switch so that input voltage is converted to output voltage; And

One control circuit, couples with this power stage circuit, and this control circuit comprises:

One PWM circuit, according to a feedback signal, to produce a pulse width modulation signal; And

One moulding weighting circuit, couples with this PWM circuit, to receive this pulse width modulation signal, and according to this input voltage, by this pulse width modulation signal, each cycle rise edge or fall edge occur time point, postpone one section of Preset Time, and then produce this driving signal.

2. switched power supply as claimed in claim 1, wherein, this Preset Time extends when this input voltage rises, shortens when this input voltage declines.

3. switched power supply as claimed in claim 2, wherein, this Preset Time is proportional to this input voltage or is proportional to the variable quantity of this input voltage in the unit interval.

4. switched power supply as claimed in claim 1, wherein, this power stage circuit comprises a transformer circuit.

5. switched power supply as claimed in claim 1, wherein, this moulding weighting circuit comprises:

One slope generating circuit, in order to produce a slope, this slope generating circuit receives this pulse width modulation signal as frequency, and the Slope Facies that produces of this slope generating circuit is about the inverse of this input voltage; And

An accurate comparator, the slope produced by this slope generating circuit is compared with a reference level, and produces aforementioned driving signal according to comparative result.

6. switched power supply as claimed in claim 1, wherein, this moulding weighting circuit comprises:

One slope generating circuit, in order to produce a slope, this slope generating circuit receives this pulse width modulation signal as frequency; And

An accurate comparator, the slope produced by this slope generating circuit compared with the positive ratio of this input voltage, and produces aforementioned driving signal according to comparative result.

7. the control circuit of a switched power supply, wherein this switched power supply is in order to be converted to output voltage by input voltage, comprise a power stage circuit, signal is driven according to one, switch wherein at least one power switch so that input voltage is converted to output voltage, it is characterized in that, described control circuit comprises:

One PWM circuit, according to a feedback signal, to produce a pulse width modulation signal; And

One moulding weighting circuit, couples with this PWM circuit, to receive this pulse width modulation signal, and according to this input voltage, by this pulse width modulation signal, each cycle rise edge or fall edge occur time point, postpone one section of Preset Time, and then produce this driving signal.

8. the control circuit of switched power supply as claimed in claim 7, wherein, this Preset Time extends when this input voltage rises, shortens when this input voltage declines.

9. the control circuit of switched power supply as claimed in claim 8, wherein, this Preset Time is proportional to this input voltage or this input voltage variable quantity.

10. the control circuit of switched power supply as claimed in claim 7, wherein, this power stage circuit comprises a transformer circuit.

The control circuit of 11. switched power supplies as claimed in claim 7, wherein, this moulding weighting circuit comprises:

One slope generating circuit, in order to produce a slope, this slope generating circuit receives this pulse width modulation signal as frequency, and the Slope Facies that produces of this slope generating circuit is about the inverse of this input voltage; And

An accurate comparator, the slope produced by this slope generating circuit is compared with a reference level, and produces aforementioned driving signal according to comparative result.

The control circuit of 12. switched power supplies as claimed in claim 7, wherein, this moulding weighting circuit comprises:

One slope generating circuit, in order to produce a slope, this slope generating circuit receives this pulse width modulation signal as frequency; And

An accurate comparator, the slope produced by this slope generating circuit compared with the positive ratio of this input voltage, and produces aforementioned driving signal according to comparative result.

The control method of 13. 1 kinds of switched power supplies, wherein this switched power supply is in order to be converted to output voltage by input voltage, comprise a power stage circuit, signal is driven according to one, switch wherein at least one power switch so that input voltage is converted to output voltage, it is characterized in that, the control method of described switched power supply comprises:

According to a feedback signal, to produce a pulse width modulation signal; And

Receive this pulse width modulation signal, and according to this input voltage, by this pulse width modulation signal, rising edge or falling the time point that edge occurs of each cycle, postpones one section of Preset Time, and then produces this driving signal.

The control method of 14. switched power supplies as claimed in claim 13, wherein, this Preset Time extends when this input voltage rises, shortens when this input voltage declines.

The control method of 15. switched power supplies as claimed in claim 14, wherein, this Preset Time is proportional to this input voltage or or is proportional to the variable quantity of this input voltage in the unit interval.