CN114825877A - Self-adaptive on-time circuit for reducing no-load ripple - Google Patents

Self-adaptive on-time circuit for reducing no-load ripple Download PDF

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CN114825877A
CN114825877A CN202210585977.9A CN202210585977A CN114825877A CN 114825877 A CN114825877 A CN 114825877A CN 202210585977 A CN202210585977 A CN 202210585977A CN 114825877 A CN114825877 A CN 114825877A
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voltage
circuit
power supply
gate
time
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向本才
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Hangzhou Weimeidi Semiconductor Co ltd
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Hangzhou Weimeidi Semiconductor Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output

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  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention belongs to the technical field of electronic circuits, and particularly relates to a self-adaptive on-time circuit for reducing no-load ripples. The invention mainly adopts a charging circuit to generate a ramp wave aligned with a control signal, the ramp wave voltage is compared with a threshold voltage generated by a reference circuit through a comparator to generate a conduction time control signal, then an output signal corresponding to the discharge time of a switching power supply is generated through the control circuit to control the reference circuit, wherein the reference circuit comprises three divider resistors connected in series and a filter branch connected to the comparator, and a switch is used for controlling the short circuit of the third divider resistor in the reference circuit. The invention can keep the switching power supply ripple consistent under any condition.

Description

Self-adaptive on-time circuit for reducing no-load ripple
Technical Field
The invention belongs to the technical field of electronic circuits, and particularly relates to a self-adaptive on-time circuit for reducing no-load ripples.
Background
Along with the technical development, in order to meet market demands, the requirements on the switching power supply are higher and higher, the switching power supply is generally required to have the advantages of high response speed and the like, and the switching power supply with a fixed conduction time mode is gradually developed. As shown in fig. 1, in the conventional fixed on-time switching power supply, a fixed on-time is obtained by an on-time circuit Ton, and the feedback voltage Vfb is compared with the reference voltage Vref to control the output voltage to be stabilized at a preset voltage value, so as to achieve the effect of voltage stabilization.
During heavy load/full load, the switching power supply with the fixed on-time mode works in a continuous current mode, the inductive current IL rises within the on-time Ton, the inductive current IL falls within the off-time Toff, the inductive current IL is a triangular wave, and the peak value of the inductive current IL is Ipeak. When the fixed on-time mode switching power supply works in the continuous current mode, the output ripple is the voltage drop generated by the inductor current IL on the output capacitor Cout, and the value is
Figure BDA0003665955630000011
Figure BDA0003665955630000012
During no-load/light load, the fixed on-time mode switching power supply works in an interrupted current mode, the inductive current IL rises within the on-time Ton, the inductive current IL falls within the off-time Toff, the inductive current is 0 within the discharge time Tdis, and the inductive current IL is an interrupted triangular wave with a peak value Ipeak. When the fixed on-time mode switching power supply works in an interrupted current mode, the output ripple is inductive current IL and charges an output capacitor Cout, and the single charge Qc and the ripple Vriple are
Figure BDA0003665955630000013
Figure BDA0003665955630000014
Note that the no-load charging time Tch and the full-load duty cycle time Tsw are the same, and Fsw and Tsw are design parameters of the fixed on-time mode switching power supply, and the values are respectively
Tsw＝K×R×C
Figure BDA0003665955630000015
Wherein, R is the voltage-controlled parameter of the first power supply of the charging circuit of the conduction time circuit, C is the capacitance value of the first charging capacitor of the charging circuit of the conduction time circuit, and K is the voltage division ratio of the reference circuit divider resistor of the conduction time circuit.
The ripples of heavy and light loads can be expressed as
Figure BDA0003665955630000021
Figure BDA0003665955630000022
It can be seen that the conventional fixed on-time mode switching power supply and the adaptive on-time circuit thereof cannot keep the switching power supply ripple consistent under any condition, and the ripple will increase by about 3 times during no-load/light load. Therefore, it is desirable to provide a fixed on-time mode switching power supply and an adaptive on-time circuit thereof that optimize the no-load/light-load ripple.
Disclosure of Invention
In view of the above problems, the present invention provides an adaptive on-time circuit for reducing no-load ripple.
The technical scheme of the invention is as follows:
a self-adaptive conduction time circuit for reducing no-load ripples is used for a switching power supply, the switching power supply comprises a conduction time circuit, a driving circuit, a high-side power tube and a low-side power tube, wherein the driving circuit generates driving signals for driving the high-side power tube and the low-side power tube to be started according to conduction time control signals output by the conduction time circuit, and the connection point of the high-side power tube and the low-side power tube generates output voltage after passing through an inductor, so that the output voltage is defined as Vout; the conduction time circuit is a self-adaptive conduction time circuit and comprises a charging circuit, a reference circuit, a comparator and a control circuit;
the charging circuit is used for generating a ramp wave aligned with the control signal and comprises a first power supply, a first capacitor and a first switch, wherein one end of the first power supply is connected with an input voltage, the other end of the first power supply is respectively connected with a non-inverting input end of a comparator, one end of the first capacitor and one end of the first switch, and the other end of the first capacitor and the other end of the first switch are grounded; the enabling signal of the first switch is a control signal, and the control signal is a turn-on time control voltage; the first power supply is a voltage-controlled current source, and the current magnitude of the first power supply is controlled by input voltage;
the reference circuit is used for generating a comparator threshold voltage related to the output voltage Vout, and comprises a first voltage dividing resistor, a second voltage dividing resistor, a third voltage dividing resistor, a second switch, a filter resistor and a second capacitor; the output voltage Vout sequentially passes through the first voltage-dividing resistor, the second voltage-dividing resistor and the third voltage-dividing resistor and then is grounded, the connection point of the first voltage-dividing resistor and the second voltage-dividing resistor is defined as a first voltage-dividing node, the connection point of the second voltage-dividing resistor and the third voltage-dividing resistor is defined as a second voltage-dividing ground, the first voltage-dividing node passes through the filter resistor and then is connected with the inverting input end of the comparator and one end of the second capacitor, and the other end of the second capacitor is grounded; the second voltage division node is connected with one end of a second switch, the other end of the second switch is grounded, and an enable signal of the second switch is an output signal of the control circuit;
the comparator is used for comparing the ramp voltage generated by the charging circuit with the threshold voltage generated by the reference circuit and outputting a conduction time control signal;
the control circuit is used for generating an output signal corresponding to the discharge time of the switching power supply to control the on-off of the second switch, so that the switching power supply is in an intermittent current mode, the threshold voltage of the comparator is Kch × Vout in the charge time and is Kdis × Vout in the discharge time, wherein:
Figure BDA0003665955630000031
Figure BDA0003665955630000032
r206 is the filter resistor value, R210 is the third divider resistor value, and R205 is the second divider resistor value.
Further, the control circuit is an or gate, and the driving signal of the high-side power tube is defined as Vgh, and the driving signal of the low-side power tube is defined as Vgl, so that one input end of the or gate is connected with Vgh, and the other input end of the or gate is connected with Vgl.
Furthermore, the control circuit comprises a first exclusive-or gate and a second exclusive-or gate, wherein a first input end of the first exclusive-or gate is connected with a control signal, and a second input end of the first exclusive-or gate is connected with an output end of the second exclusive-or gate; the first input end of the second exclusive-OR gate is connected with the input end of the first exclusive-OR gate, the second input end of the second exclusive-OR gate is connected with the zero-crossing detection signal, and the output end of the second exclusive-OR gate is the output end of the control circuit.
The invention has the beneficial effect that the invention can keep the switching power supply ripples consistent under any condition.
Drawings
Fig. 1 shows a switching power supply of a conventional on-time circuit.
Fig. 2 shows a conventional on-time circuit.
Fig. 3 shows how and how output ripples are generated at different load currents.
Fig. 4 is a waveform diagram showing a conventional switching power supply using an on-time circuit, in which the on-time Ton is the same and the charging time Tch for a light load and the duty cycle time Tsw for a heavy load are the same for different load currents.
Fig. 5 is a switching power supply showing an adaptive on-time circuit of the present invention for reducing idle ripple.
Fig. 6 is a waveform diagram illustrating a switching power supply of an adaptive on-time circuit for reducing idle ripple according to the present invention. The on-time Ton is different for different loads.
Fig. 7 is a diagram illustrating an adaptive on-time circuit for reducing idle ripple in accordance with the present invention.
Fig. 8 shows an adaptive on-time circuit for reducing idle ripple according to the present invention, which includes an implementation of the control circuit 220.
Fig. 9 shows an adaptive on-time circuit for reducing idle ripple according to the present invention, which includes an implementation of the control circuit 220.
Detailed Description
The technical method of the present invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 7, the circuit of the present invention includes:
a charging circuit for generating a ramp wave aligned with the control signal. The charging circuit is implemented by a first power supply 201, a first charging capacitor 202 and a first switch 202. The first power source is a voltage-controlled current source, the current magnitude of which is controlled by the input voltage, and the current value of which is Vin/R.
The reference circuit is used for generating a comparator threshold voltage related to the output voltage Vout. The reference circuit is implemented by a first voltage dividing resistor 204, a second voltage dividing resistor 205, a third voltage dividing resistor 210, a second switch 209, and by a first filter resistor 206 and a first filter capacitor 207. The first voltage dividing resistor 204, the second voltage dividing resistor 205 and the third voltage dividing resistor 210 form a voltage dividing resistor network. The first filter resistor 206 and the first filter capacitor 207 form a low-pass filter to stabilize the threshold voltage of the comparator.
And a comparator 208 for comparing the ramp voltage generated by the charging circuit with the threshold voltage generated by the reference circuit.
And the control circuit 220 is used for generating a control signal Vdis corresponding to the discharge time of the switching power supply so as to control the on-off of the second switch 209, so that the switching power supply is in an intermittent current mode, the threshold voltage of the comparator is Kch Vout within the charging time Tch, and is Kdis Vout within the discharging time Tdis. An adaptive on-time circuit of fixed frequency discontinuous current mode incorporating a specific control circuit may be embodied by fig. 8-9.
Under heavy load/full load, the discharge time Tdis is not existed, the design is obviously the same as the existing general design, the cycle time Tsw and the working frequency Fsw are
Figure BDA0003665955630000041
Tswhl＝Kch×R×C
Figure BDA0003665955630000042
During no load/light load, the period time Tsw may be divided into a charging time Tch and a discharging time Tdis of the output capacitor, where the charging time Tch may be further divided into an on time Ton and an off time Toff of the switching power supply.
Figure BDA0003665955630000051
Tswll＝Kdis×R×C
Figure BDA0003665955630000052
The ratio of Kch to Kdis can be made to be about 1.77 by selecting a proper resistance ratio
Figure BDA0003665955630000053
The unloaded ripple can now be made comparable to the full-load ripple, i.e.
Figure BDA0003665955630000054
As described above, even in the idling state, the output ripple of the switching power supply is the same as that in the heavy load state.
Fig. 8 and 9 show 2 specific implementations of the present invention, particularly the control circuit 220 included therein. The main innovation of the present invention is the method of fixing the operating frequency in the discontinuous current mode, fig. 8 and fig. 9 mainly demonstrate the feasibility of the invention, and the invention is not limited to the specific implementation shown in fig. 8 and fig. 9.
Since the above output voltage Vout is the output voltage of the switching power supply, and Vout is the filtered output of Vsw, and Vout is Vin × Ton/(Ton + Toff), Vout input in the drawings (fig. 2, 7, 8, and 9) may be Vout of the switching power supply, Vsw of the switching power supply, or Vin controlled by Ton.
The above input voltage Vin is the input voltage of the switching power supply, and since Vin charges the capacitor only in the Ton stage, Vout input in the drawings (fig. 2, 7, 8, and 9) may be Vout or Vsw of the switching power supply.

Claims (3)

1. A self-adaptive conduction time circuit for reducing no-load ripples is used for a switching power supply, the switching power supply comprises a conduction time circuit, a driving circuit, a high-side power tube and a low-side power tube, wherein the driving circuit generates driving signals for driving the high-side power tube and the low-side power tube to be started according to conduction time control signals output by the conduction time circuit, and the connection point of the high-side power tube and the low-side power tube generates output voltage after passing through an inductor, so that the output voltage is defined as Vout; the on-time circuit is a self-adaptive on-time circuit and comprises a charging circuit, a reference circuit, a comparator and a control circuit;
the charging circuit is used for generating a ramp wave aligned with the control signal and comprises a first power supply, a first capacitor and a first switch, wherein one end of the first power supply is connected with an input voltage, the other end of the first power supply is respectively connected with a non-inverting input end of a comparator, one end of the first capacitor and one end of the first switch, and the other end of the first capacitor and the other end of the first switch are grounded; the enabling signal of the first switch is a control signal, and the control signal is a turn-on time control voltage; the first power supply is a voltage-controlled current source, and the current magnitude of the first power supply is controlled by input voltage;
the reference circuit is used for generating a comparator threshold voltage related to the output voltage Vout, and comprises a first voltage dividing resistor, a second voltage dividing resistor, a third voltage dividing resistor, a second switch, a filter resistor and a second capacitor; the output voltage Vout sequentially passes through the first voltage-dividing resistor, the second voltage-dividing resistor and the third voltage-dividing resistor and then is grounded, the connection point of the first voltage-dividing resistor and the second voltage-dividing resistor is defined as a first voltage-dividing node, the connection point of the second voltage-dividing resistor and the third voltage-dividing resistor is defined as a second voltage-dividing ground, the first voltage-dividing node passes through the filter resistor and then is connected with the inverting input end of the comparator and one end of the second capacitor, and the other end of the second capacitor is grounded; the second voltage division node is connected with one end of a second switch, the other end of the second switch is grounded, and an enable signal of the second switch is an output signal of the control circuit;
the comparator is used for comparing the ramp voltage generated by the charging circuit with the threshold voltage generated by the reference circuit and outputting a conduction time control signal;
the control circuit is used for generating an output signal corresponding to the discharge time of the switching power supply to control the on-off of the second switch, so that the switching power supply is in an intermittent current mode, the threshold voltage of the comparator is Kch × Vout in the charge time and is Kdis × Vout in the discharge time, wherein:
Figure FDA0003665955620000011
Figure FDA0003665955620000012
r206 is the filter resistor value, R210 is the third divider resistor value, and R205 is the second divider resistor value.
2. The adaptive on-time circuit for reducing no-load ripple of claim 1, wherein the control circuit is an or gate, and the driving signal of the high-side power transistor is defined as Vgh, and the driving signal of the low-side power transistor is defined as Vgl, and one input terminal of the or gate is connected to Vgh, and the other input terminal of the or gate is connected to Vgl.
3. The adaptive on-time circuit for reducing no-load ripple according to claim 1, wherein the control circuit comprises a first exclusive or gate and a second exclusive or gate, a first input of the first exclusive or gate is connected to the control signal, and a second input of the first exclusive or gate is connected to an output of the second exclusive or gate; the first input end of the second exclusive-OR gate is connected with the input end of the first exclusive-OR gate, the second input end of the second exclusive-OR gate is connected with the zero-crossing detection signal, and the output end of the second exclusive-OR gate is the output end of the control circuit.
CN202210585977.9A 2022-05-27 2022-05-27 Self-adaptive on-time circuit for reducing no-load ripple Pending CN114825877A (en)

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