A valley conduction circuit and a switching power supply circuit using the same

Abstract

The application discloses a trough conduction circuit and a switching power supply circuit using the same. The trough conduction circuit comprises a differential circuit, a resonant current zero-crossing detector, a trough identifier and an opening judgment controller connected in sequence. The differential circuit is connected to a primary side, a secondary side or an auxiliary winding of a transformer in the switching power supply circuit. The opening judgment controller is connected to a PWM logic controller in the switching power supply circuit. The trough conduction circuit converts a resonant voltage signal on the primary side, the secondary side or the auxiliary winding into a resonant current signal. The zero-crossing point of the resonant current signal is detected, i.e. the peak and trough signals of the resonant voltage signal on the primary side, the secondary side or the auxiliary winding. The current zero-crossing signal is identified and separated, so that the trough signal corresponding to the resonant voltage is obtained. The power switch is opened by the identified trough signal. The application solves the zero-voltage conduction problem of the traditional switching power supply, and improves the overall efficiency and EMI.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of AC / DC switching power supply, in particular to a valley conduction circuit of AC / DC flyback converter and a switching power supply circuit using the same. BACKGROUND

[0002] For AC / DC switching power supply circuit, the conduction of power switch is traditionally triggered by the rising edge or falling edge of the internal clock of the chip, or by the zero-crossing point of the voltage resonance waveform, the former is called hard switching, and the latter is called quasi-resonance. With the improvement of energy-saving awareness and the world's requirement for energy saving, the energy efficiency standard is getting higher and higher, that is, the loss is required to be small and the efficiency is required to be high. Under hard switching, the power consumption on the power switch is very high at the moment of switching on, because the drain voltage (or collector voltage) of the power switch is very high. Therefore, reducing the voltage drop on the power switch at the moment of turning on can reduce the switching loss. Since the voltage at the moment of turning off the power switch is uncontrollable, but the moment of turning on the power switch can be selected, and the moment when the Vds voltage is low can be selected to turn on the power switch, which is quasi-resonant switching on.

[0003] Although the current quasi-resonant technology has improved the efficiency compared with hard switching, since it does not realize zero-voltage conduction, the conduction loss still exists.

[0004] The traditional valley detection is to detect whether it is the valley of resonance by directly detecting the resonance voltage. Due to the chip manufacturing process, each pin of the chip is provided with an ESD protection circuit. If the resonance voltage is directly connected to the pin of the chip, the ESD diode will be turned on when the resonance voltage is negative, which will clamp the negative voltage of the resonance, so that the chip cannot detect the valley of the resonance. The present application solves this problem. SUMMARY

[0005] In view of the problem of non-zero Vds (Vce) voltage on the power device at the moment of turning on in the prior art, the present application improves the turning on of the power tube when the voltage drop on the power tube is zero, solving the switching loss problem of hard switching or quasi-resonant switching in the traditional technology.

[0006] In addition, the present application uses a differential circuit to convert the resonance voltage waveform into a current waveform, and the differential element uses a capacitor, so as to isolate the resonance waveform from the pin of the chip. Therefore, the problem of valley information loss when the resonance voltage is negative is solved. The so-called valley information loss refers to that if the resonance voltage is directly connected to the pin of the chip, the ESD diode of the chip pin will be turned on when the resonance voltage is negative, which will clamp the negative voltage to-0.7V, thereby shielding the valley information and causing the loss of valley information.

[0007] The micro-differential capacitor of the present application is integrated in a chip, in the form of MIM (Metal-Isolation-Metal), and can also be placed outside the chip to achieve the same function.

[0008] The object of the present application is achieved by the following technical solutions.

[0009] According to the first aspect of the present application, a wave trough conduction circuit is provided for a switching power supply circuit, comprising: a differential circuit, a resonant current zero-crossing detector, a wave trough identifier, and an opening judgment controller connected in sequence; wherein the differential circuit is connected to a primary side, a secondary side or an auxiliary winding of a transformer in the switching power supply circuit, and the opening judgment controller is connected to a PWM logic controller in the switching power supply circuit.

[0010] Further, the wave trough conduction circuit converts the resonant voltage signal on the primary side, the secondary side or the auxiliary winding into a resonant current signal, detects the zero-crossing point of the resonant current signal as the wave peak and wave trough signals of the resonant voltage signal, and identifies and separates the zero-crossing point of the resonant current signal to obtain the wave trough signal corresponding to the resonant voltage signal, and the power switch of the switching power supply circuit is opened by the wave trough signal.

[0011] Further, the differential circuit is configured to receive a resonant voltage signal, convert the received resonant voltage signal into a resonant current signal, and send the resonant current signal into the resonant current zero-crossing detector;

[0012] The resonant current zero-crossing detector detects the zero-crossing point of the resonant current signal as the wave peak and wave trough signals of the resonant voltage signal.

[0013] The wave trough identifier identifies and separates the zero-crossing point of the resonant current signal to obtain the wave trough signal corresponding to the resonant voltage signal.

[0014] The opening judgment controller receives the wave trough signal identified by the wave trough identifier, judges in combination with a built-in clock, and sends out an opening signal.

[0015] Further, the differential circuit includes a first capacitor, the anode of the first capacitor is connected to a sampled resonant voltage, and the resonant voltage is the voltage on the primary side, the secondary side or the auxiliary winding; the cathode of the first capacitor is connected to the input of the resonant current zero-crossing detector.

[0016] Further, the resonant current zero-crossing detector includes a first resistor and a comparator.

[0017] The anode of the first resistor is connected to the cathode of the first capacitor, and the cathode of the first resistor is connected to the ground.

[0018] The inverting input terminal of the first comparator is connected to ground, and the non-inverting input terminal is connected to the anode of the first resistor.

[0019] Further, the trough identifier comprises a first inverter, a second inverter, a third inverter, a first NAND gate, a fourth inverter, and a second capacitor; wherein the input of the first inverter is connected to the output of the first comparator, the output of the first inverter is connected to the anode of the second capacitor, and the cathode of the second capacitor is connected to ground; the input of the second inverter is connected to the output of the first inverter, and the output of the second inverter is connected to the input of the third inverter; the output of the third inverter is connected to the first input of the first NAND gate, the second input of the first NAND gate is connected to the input of the first inverter, and the output of the first NAND gate is connected to the input of the fourth inverter.

[0020] Further, the start judgment controller comprises a second NAND gate, a delay unit, a fifth inverter, a first NOR gate, and a sixth inverter; wherein the first input of the second NAND gate is connected to the output of the fourth inverter, the second input of the second NAND gate is connected to the internal clock, the output of the second NAND gate is connected to the input of the fifth inverter; the output of the fifth inverter is connected to the first input of the first NOR gate; the first input of the delay unit is connected to the output of the second NAND gate, the second input of the delay unit is connected to the internal clock, and the output of the delay unit is connected to the second input of the first NOR gate; the output of the first NOR gate is connected to the input of the sixth inverter, and the output of the sixth inverter is the output of the start judgment controller.

[0021] Further, the differential circuit is a passive differential circuit or an active differential circuit.

[0022] According to a second aspect of the present application, a switching power supply circuit is provided, which comprises a trough conduction circuit according to the first aspect.

[0023] Further, the switching power supply circuit further comprises a power switch, a PWM comparator, a PWM logic controller, and an output driver; wherein the input of the PWM logic controller is connected to the output of the start judgment controller and the output of the PWM comparator, the output of the PWM logic controller is connected to the input of the output driver, and the output of the output driver is connected to the gate of the power switch; the source of the power switch is connected to the input of the PWM comparator, and the drain of the power switch is connected to the primary side of the transformer.

[0024] The present application has the advantage that the trough conduction technology applied to AC / DC solves the zero voltage conduction problem of the traditional switching power supply, and improves the overall efficiency and EMI. BRIEF DESCRIPTION OF DRAWINGS

[0025] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0026] Appendix Figure 1 A schematic diagram of an AC / DC switching power supply circuit according to an embodiment of the present invention is shown.

[0027] Appendix Figure 2 A schematic diagram of a valley conduction circuit according to an embodiment of the present invention is shown;

[0028] Appendix Figure 3 A timing diagram for signal control of a trough conduction circuit according to an embodiment of the present invention is shown. Detailed Implementation

[0029] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0030] Appendix Figure 1 A schematic diagram of an AC / DC switching power supply circuit according to an embodiment of the present invention is shown; as follows: Figure 1 As shown, the AC input of the AC / DC switching power supply circuit, after EMI filtering, is input to the NP terminal of the transformer T. The NP terminal is also connected to the D terminal (drain) of the MOSFET transistor SW (acting as a power switch). The S terminal (source) of the MOSFET transistor SW is grounded through a resistor and is also connected to the PWM comparator 50. The G terminal (gate) of the MOSFET transistor SW is connected to the output driver 70. The PWM logic controller 60 is connected to the PWM comparator 50, the output driver 70, and the trough conduction circuit 10. One end of the PWM comparator 50 is connected to the Vcc power supply to receive power. The NA terminal of the transformer T is connected to the trough conduction circuit 10.

[0031] The circuit implementation of the PWM comparator 50, PWM logic controller 60, and output driver 70 is not limited and is a common implementation method existing in the art. It is not the inventive point of this invention and will not be described in detail here.

[0032] The trough conduction circuit 10 includes a differentiating circuit 110, a resonant current zero-crossing detector 120, a trough identifier 130, and an on-time determination controller 140 connected in sequence. The differentiating circuit 110 is connected to the NA terminal of the transformer T, while the on-time determination controller 140 is connected to the PWM logic controller 60. Furthermore, the on-time determination controller 140 is time-controlled by the clock signal CLK. The trough conduction circuit 10 detects the trough signal of the resonant voltage on the primary side (transformer primary, auxiliary winding, and secondary side) of the switching power supply, and coordinates with the internal clock signal CLK to generate an on-time signal that controls the power switch to conduct. The differentiating circuit 110 is configured to receive the resonant voltage signal, convert the received resonant voltage into a resonant current, and send it to the resonant current zero-crossing detector 120. The resonant current zero-crossing detector 120 sends the identified zero-crossing signal to the trough identifier 130. The on-time determination controller 140 compares the received trough signal identified by the trough identifier 130 with its internal clock signal and sends out an on-time signal. The trough conduction circuit 10 converts the resonant voltage signal on the primary side, secondary side, or auxiliary winding into a resonant current signal. By detecting the zero-crossing point of the resonant current signal, the peak and trough signals of the resonant voltage signal on the primary side, secondary side, or auxiliary winding are obtained. The trough signal corresponding to the resonant voltage is obtained by identifying and separating the current zero-crossing signal. The power switch is turned on by the identified trough signal.

[0033] The circuit connected after the NS terminal of transformer T is a DC output circuit, including diode DS, capacitor Co, resistors R1 and R2, etc., to output DC voltage Vo. The circuit implementation of the DC output circuit is not limited, and it is a common implementation method existing in the art, which is not the inventive point of this invention, and will not be described in detail here.

[0034] Appendix Figure 2 A schematic diagram of a valley conduction circuit according to an embodiment of the present invention is shown; as follows: Figure 2 As shown, the differentiating circuit 110 includes a first capacitor C1. The anode of the first capacitor is connected to the sampled resonant voltage. This resonant voltage is the resonant voltage generated by the main inductor (primary side inductor) and parasitic capacitance after the power MOS is turned off. It can be the voltage on the primary side, secondary side, or auxiliary winding. The cathode of the first capacitor is connected to the input of the resonant current zero-crossing detector 120.

[0035] Of course, the implementation of the differentiating circuit 110 is not limited to using capacitors; it can also employ passive or active differentiating circuits. The passive differentiating circuit can consist of capacitors, resistors, and capacitors. The differentiating circuit 110 converts the resonant voltage signal into a resonant current signal.

[0036] The resonant current zero-crossing detector 120 includes a first resistor R1 and a comparator COMP1. The anode of the first resistor R1 is connected to the cathode of the first capacitor C1, and the cathode of the first resistor R1 is connected to the ground. The inverting input of the first comparator COMP1 is connected to the ground, and the non-inverting input of the first comparator COMP1 is connected to the anode of the first resistor R1. The output of the first comparator COMP1 (zv signal) is connected to the input of the trough identifier 130. The resonant current zero-crossing detector 120 converts the resonant current signal into a voltage signal for detecting the current zero-crossing, or directly detects the resonant current signal without conversion.

[0037] Of course, the resonant current zero-crossing detector 120 is not limited to the above connection method, and the cathode of the first capacitor C1 can be directly connected to the non-inverting input / inverting input of the comparator COMP1, the inverting input / non-inverting input of the current comparator can be connected to the ground, or an offset voltage can be applied. Figure 2

[0038] The trough identifier 130 can be implemented by an inverter, an NAND gate, a NOT gate, a flip-flop, a comparator, etc. The goal of the trough identifier 130 is to extract the signal corresponding to the moment when the current in the resonant current zero-crossing detector 120 is zero from the trough signal of the primary side (or the secondary side, or the auxiliary winding) of the transformer, and in this example, the rising edge of the resonant current zero-crossing detector 120 is extracted, i.e., the trough signal.

[0039] Specifically, the trough identifier 130 includes a first inverter inv1, a second inverter inv2, a third inverter inv3, a first NAND gate nand1, a fourth inverter inv4, and a second capacitor C2. The input of the first inverter inv1 is connected to the output of the first comparator COMP1, the output of the first inverter inv1 is connected to the anode of the second capacitor C2, and the cathode of the second capacitor C2 is connected to the ground. The input of the second inverter inv2 is connected to the output of the first inverter inv1, and the output of the second inverter inv2 is connected to the input of the third inverter inv3. The output of the third inverter inv3 is connected to the first input of the first NAND gate nand1, the second input of the first NAND gate nand1 is connected to the input of the first inverter inv1, and the output of the first NAND gate nand1 is connected to the input of the fourth inverter inv4.

[0040] ​The opening judgment controller 140 comprises a second NAND gate nand2, a delay unit, a fifth inverter inv5, a first NOR gate nor1, and a sixth inverter inv6. The first input end of the second NAND gate nand2 is connected with the output (signal valley) of the fourth inverter inv4, the second input end of the second NAND gate nand2 is connected with the internal clock CLK, the output of the second NAND gate nand2 is connected with the input of the fifth inverter inv5; the output of the fifth inverter inv5 is connected with the first input end of the first NOR gate nor1; the reset end (i.e. the first input end) of the delay unit is connected with the output of the second NAND gate nand2, the second input end of the delay unit is connected with the internal clock CLK, and the output (signal ckd) of the delay unit is connected with the second input end of the first NOR gate nor1; the output of the first NOR gate nor1 is connected with the input of the sixth inverter inv6, and the output (signal gate_on) of the sixth inverter inv6 is the output of the opening judgment controller 140.

[0041] The function realized by the opening judgment controller 140 is as follows: when the internal clock sends an opening enable, the power switch is opened after the opening enable is sent and timing is started; if an effective valley signal is not detected within 2us, the power switch is opened immediately after the timing is ended.

[0042] The auxiliary winding voltage Vaux is shown in the following figure. Figure 3 The signal control timing diagram of the valley conduction circuit according to the embodiment of the present application is shown.

[0043] Vaux is the voltage waveform of the auxiliary winding NA, which is coupled with the waveform of the primary winding NP. Due to the same end of NP and NA (black dot), the voltage of Vaux is wherein is the turns ratio of the transformer. When the power MOS SW is turned off, the voltage of Vaux is positive, and the value is approximately equal to the output voltage (refer to Figure 1 ).

[0044] I aux is the voltage of the auxiliary winding NA, which is converted into current, representing the current value.

[0045] The present application mainly solves the problem of accurately detecting the valley value of the voltage of Vaux (the valley is negative voltage). In the traditional voltage detection method, due to the existence of negative voltage of Vaux, and the negative voltage can reach negative tens of volts, the ESD device of the chip pin will clamp the negative voltage to -0.7V, so the valley information will be filtered out, resulting in inaccurate detection. The idea of the present application is to convert the voltage into current through a differential circuit. Due to the decaying sinusoidal signal, for example, the expression and the following formula are in a proportional relationship:

[0046] Therefore, by the differential circuit, the crest and trough of the voltage are resolved into the zero-crossing points of the current signal (the crest and trough of the voltage signal have zero differential value), and then the current waveform is converted into the voltage waveform, and the zero-crossing points of the voltage waveform are detected, i.e. the crest and trough are detected.

[0047] The comparator COMP1 is used to detect the crest and trough signals, the rising edge of ZV corresponds to the trough signal, and the falling edge of ZV corresponds to the crest signal.

[0048] The rising edge of ZV is taken out by INV1, C2, INV2, INV3, nand1 and inv4, i.e. the trough is extracted.

[0049] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A trough conduction circuit for use in a switching power supply circuit, characterized in that, The wave trough conduction circuit comprises: a differential circuit, a resonant current zero-crossing detector, a wave trough identifier, and an opening judgment controller connected in sequence; the differential circuit is connected to a primary side, a secondary side, or an auxiliary winding of a transformer in the switching power supply circuit, and the opening judgment controller is connected to a PWM logic controller in the switching power supply circuit; the wave trough identifier comprises a first inverter, a second inverter, a third inverter, a first NAND gate, a fourth inverter, and a second capacitor; the output of the first inverter is connected to the anode of the second capacitor, and the cathode of the second capacitor is grounded; the input of the second inverter is connected to the output of the first inverter, and the output of the second inverter is connected to the input of the third inverter; the output of the third inverter is connected to the input of the first NAND gate, the input of the first NAND gate is connected to the input of the first inverter, and the output of the first NAND gate is connected to the input of the fourth inverter; the input of the first inverter is connected to the output of the resonant current zero-crossing detector, and the output of the fourth inverter is connected to the input of the opening judgment controller.

2. The wave trough conduction circuit according to claim 1, wherein the wave trough conduction circuit converts a resonant voltage signal on the primary side, the secondary side, or the auxiliary winding into a resonant current signal, detects a zero-crossing point of the resonant current signal as a wave peak and wave trough signal of the resonant voltage signal, identifies and separates the zero-crossing point of the resonant current signal to obtain a wave trough signal corresponding to the resonant voltage signal, and turns on a power switch of the switching power supply circuit by the wave trough signal.

3. The wave trough conduction circuit according to claim 1 or 2, wherein the differential circuit is configured to receive a resonant voltage signal, convert the received resonant voltage signal into a resonant current signal, and send the resonant current signal into the resonant current zero-crossing detector; the resonant current zero-crossing detector detects a zero-crossing point of the resonant current signal as a wave peak and wave trough signal of the resonant voltage signal; the wave trough identifier identifies and separates the zero-crossing point of the resonant current signal to obtain a wave trough signal corresponding to the resonant voltage signal; the opening judgment controller receives the wave trough signal identified by the wave trough identifier, judges in combination with a built-in clock, and sends out an opening signal to turn on a power switch of the switching power supply circuit.

4. The wave trough conduction circuit according to claim 1, wherein the differential circuit comprises a first capacitor, the anode of the first capacitor is connected to a sampled resonant voltage, the resonant voltage is a voltage on the primary side, the secondary side, or the auxiliary winding, and the cathode of the first capacitor is connected to the input of the resonant current zero-crossing detector.

5. The wave trough conduction circuit according to claim 1 or 4, wherein the resonant current zero-crossing detector comprises a first resistor and a comparator; the anode of the first resistor is connected to the cathode of the first capacitor, and the cathode of the first resistor is grounded; the inverting input of the first comparator is grounded, the non-inverting input of the first comparator is connected to the anode of the first resistor, and the output of the first comparator is connected to the input of the wave trough identifier.

6. The wave trough conduction circuit according to claim 5, wherein The start judgment controller comprises a second NAND gate, a delay unit, a fifth inverter, a first NOR gate and a sixth inverter; wherein the first input end of the second NAND gate is connected with the output of the fourth inverter, the second input end of the second NAND gate is connected with the internal clock, the output of the second NAND gate is connected with the input of the fifth inverter; the output of the fifth inverter is connected with the first input end of the first NOR gate; the first input end of the delay unit is connected with the output of the second NAND gate, the second input end of the delay unit is connected with the internal clock, and the output of the delay unit is connected with the second input end of the first NOR gate; the output of the first NOR gate is connected with the input of the sixth inverter, and the output of the sixth inverter is the output of the start judgment controller.

7. The valley conduction circuit according to claim 1, wherein the differential circuit is a passive differential circuit or an active differential circuit. The valley conduction circuit comprises the valley conduction circuit according to any one of claims 1-7.

8. A switching power supply circuit, characterized by comprising:

9. The switching power supply circuit according to claim 8, wherein the switching power supply circuit further comprises a power switch, a PWM comparator, a PWM logic controller and an output driver; wherein the input end of the PWM logic controller is connected with the output end of the start judgment controller and the output end of the PWM comparator, the output end of the PWM logic controller is connected with the input end of the output driver, the output end of the output driver is connected with the gate of the power switch, the source of the power switch is connected with the input end of the PWM comparator, and the drain of the power switch is connected with the primary side of the transformer. ​ ​

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