Method of operating a flyback power converter

Abstract

An operating method of a flyback power converter is disclosed. The operating method includes a voltage detection pin detecting a conduction time of a power switch on a primary side of the flyback power converter, a feedback pin detecting a conduction time of a synchronous switch on a secondary side of the flyback power converter, the feedback pin detecting a number of inductor-capacitor resonance valley when the flyback power converter operates in a discontinuous conduction mode, and a high voltage detection pin detecting an input voltage input to the flyback power converter; and when the number of inductor-capacitor resonance valley is greater than a predetermined number, an operating frequency of the flyback power converter is less than a predetermined frequency, and the input voltage is less than a predetermined voltage, a controller applied to the flyback power converter makes the flyback power converter operate in a quasi-resonant mode. Therefore, compared with the prior art, the flyback power converter has better efficiency.

Description

TECHNICAL FIELD

[0001] The present invention relates to an operation method of a flyback power converter, and more particularly, to an operation method of a flyback power converter capable of switching between a quasi-resonant mode and a zero voltage switching mode to make the efficiency of the flyback power converter better. BACKGROUND

[0002] In the prior art, when a flyback power converter is designed to operate in a zero voltage switching mode, the flyback power converter has the advantage that the switching loss of the power switch on the primary side thereof approaches zero. Although the flyback power converter has the advantage that the switching loss of the power switch approaches zero, when the input voltage input to the flyback power converter is lower than a predetermined voltage or the load coupled to the secondary side of the flyback power converter is light, the efficiency of the flyback power converter operating in the zero voltage switching mode becomes worse. If the flyback power converter is operated in a quasi-resonant mode at this time, the efficiency of the flyback power converter becomes better. Because the flyback power converter cannot decide to operate in the zero voltage switching mode or the quasi-resonant mode according to the input voltage and the load, the efficiency of the flyback power converter is not necessarily optimal. Therefore, how to design a flyback power converter capable of deciding to operate in the zero voltage switching mode or the quasi-resonant mode according to the input voltage and the load has become an important issue. SUMMARY

[0003] One embodiment of the present invention discloses an operation method of a flyback power converter. The operation method includes a voltage detection pin detecting the on-time of a power switch on the primary side of the flyback power converter, a feedback pin detecting the on-time of a synchronous switch on the secondary side of the flyback power converter, the feedback pin detecting the number of inductor-capacitor resonant valleys when the flyback power converter operates in a discontinuous conduction mode (DCM), and a high voltage detection pin detecting the input voltage input to the flyback power converter; and when the number of inductor-capacitor resonant valleys is greater than a predetermined number, the operating frequency of the flyback power converter is less than a predetermined frequency, and the input voltage is less than a predetermined voltage, a controller applied to the flyback power converter makes the flyback power converter operate in a quasi-resonant mode.

[0004] An operating method of a flyback power converter is disclosed. The operating method detects a turn-on time of a power switch of a primary side of the flyback power converter according to a voltage detection pin of a primary controller, detects a turn-on time of a synchronous switch of a secondary side of the flyback power converter according to a feedback pin of the primary controller, detects a number of inductance-capacitance resonance valleys when the flyback power converter operates in a discontinuous conduction mode according to the feedback pin of the primary controller, and detects an input voltage input to the flyback power converter according to a high voltage detection pin of the primary controller, and controls the flyback power converter to switch between a quasi-resonant mode and a zero voltage switching mode. Therefore, compared to the prior art, because the operating method of the flyback power converter can control the flyback power converter to switch between the quasi-resonant mode and the zero voltage switching mode, the operating method of the flyback power converter can make the efficiency of the flyback power converter better. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 is a flowchart of an operating method of a flyback power converter according to a first embodiment of the present application.

[0006] Figure 2 is a schematic diagram illustrating a flyback power converter, a primary controller and a secondary controller.

[0007] Figures 3-7 is a schematic diagram illustrating the flyback power converter operating in the zero voltage switching mode.

[0008] Figure 8 is a schematic diagram illustrating a loss of the flyback power converter corresponding to the zero voltage switching mode relative to a loss of the flyback power converter corresponding to the quasi-resonant mode when the flyback power converter operates at different operating frequencies.

[0009] Figure 9 is a schematic diagram illustrating a loss of the flyback power converter corresponding to the zero voltage switching mode relative to a loss of the flyback power converter corresponding to the quasi-resonant mode when the flyback power converter operates at different input voltages.

[0010] Figure 10 is a schematic diagram illustrating a flyback power converter and a primary controller.

[0011] In the drawings, the following reference numerals are used:

[0012] 200 flyback power converter

[0013] 202 primary controller

[0014] 204 secondary controller

[0015] 206 Power Switch

[0016] 208 Synchronous Switch

[0017] 210 Primary winding

[0018] 212 Secondary winding

[0019] 214 Transmission Circuit

[0020] 1000 Active Clamp Flyback Power Converter

[0021] 1002 Optical Coupler

[0022] 1004 switch

[0023] 1006 Clamping Capacitor

[0024] FSW operating frequency

[0025] GND1, GND2 ground level

[0026] IDSSR, IDSSW current

[0027] PRI primary side

[0028] PF scheduled frequency

[0029] PV Predetermined Voltage

[0030] PQR, PZVS loss

[0031] SEC secondary side

[0032] T0-T4 Time

[0033] VGSSW, VGSSR gate control signals

[0034] VDSSW, VDSSR trans-voltage

[0035] VIN Input Voltage

[0036] VOUT output voltage Detailed Implementation

[0037] Please refer to Figure 1 , Figure 1 This is a flowchart of an operation method for a flyback power converter disclosed in the first embodiment of the present invention, wherein... Figure 1 The operation method is to use Figure 2 The flyback power converter 200, primary controller 202, and secondary controller 204 are described in detail below:

[0038] Step 100: Begin;

[0039] Step 102: The voltage detection pin of the primary controller 202 detects the on-time TON of the power switch 206 on the primary side PRI of the flyback power converter 200; the feedback pin of the primary controller 202 detects the on-time TDIS of the synchronous switch 208 on the secondary side SEC of the flyback power converter 200; the feedback pin of the primary controller 202 detects the number of inductor-capacitor resonant valleys LCRVN when the flyback power converter 200 operates in a discontinuous conduction mode (DCM); and the high voltage detection pin of the primary controller 202 detects the input voltage VIN input to the flyback power converter 200.

[0040] Step 104: Is the number of resonant valleys of the inductor and capacitor LCRVN greater than a predetermined number? If yes, proceed to step 106; otherwise, skip to step 112.

[0041] Step 106: Is the operating frequency of the flyback power converter 200 less than a predetermined frequency PF? If yes, proceed to step 108; otherwise, skip to step 112.

[0042] Step 108: Is the input voltage VIN less than a predetermined voltage PV? If yes, proceed to step 110; otherwise, skip to step 112.

[0043] Step 110: The primary controller 202 enables the flyback power converter 200 to operate in a quasi-resonant mode, and then jumps back to step 102;

[0044] Step 112: The primary controller 202 enables the flyback power converter 200 to operate in a zero-voltage switching mode, and then jumps back to step 102.

[0045] In explanation Figure 1 Before proceeding with the operation, please refer to the instructions. Figures 3-9 ,in Figures 3-7 This is a schematic diagram illustrating the operation of the flyback power converter 200 in the zero-voltage switching mode. Figure 8 This is a schematic diagram illustrating the loss PZVS of the flyback power converter 200 in the zero-voltage switching mode versus the loss PQR of the flyback power converter 200 in the quasi-resonant mode when the flyback power converter 200 operates at different operating frequencies. Figure 9This is a schematic diagram illustrating the loss PZVS of the flyback power converter 200 in the zero-voltage switching mode versus the loss PQR of the flyback power converter 200 in the quasi-resonant mode when the flyback power converter 200 operates with different input voltages. Additionally, as... Figure 2 As shown, the flyback power converter 200 is a secondary-side regulated flyback power converter. The turns ratio of the primary winding 210 and the secondary winding 212 of the flyback power converter 200 is N, where N is a real number. The primary controller 202 and the secondary controller 204 communicate through a transmission circuit 214. The transmission circuit 214 separates the primary side PRI of the flyback power converter 200 from the secondary side SEC, and the ground level GND1 of the primary side PRI and the ground level GND2 of the secondary side SEC of the flyback power converter 200 must not be the same. Additionally, the primary controller 202 has 6 pins (not shown in the diagram). Figure 2 The 6 pins include the voltage detection pin, the feedback pin, the high voltage detection pin, a power supply voltage pin, a gate control signal pin, and a ground pin. The power supply voltage pin is used to receive a power supply voltage, and the gate control signal pin is used to output the gate control signal generated by the primary controller 202 to the power switch 206.

[0046] like Figure 3 , 4 As shown, between time T0 and time T1, because the secondary controller 204 initiates a gate control signal VGSSR to the synchronous switch 208, the voltage across the synchronous switch 208 VDSSR is zero. The direction of the current IDSSR on the secondary side of the flyback power converter 200 is shown in the figure. Figure 3 Furthermore, since the primary side PRI and the secondary side SEC of the flyback power converter 200 do not operate simultaneously, the primary controller 202 shuts off the gate control signal VGSSW to the power switch 206, and the current IDSSW of the primary side PRI of the flyback power converter 200 is zero. The voltage across the power switch 206, VDSSW, is determined by equation (1):

[0047] VDSSW=VIN+N*(VOUT) (1)

[0048] where VOUT is the output voltage of the secondary side SEC of the flyback power converter 200. In addition, between time TO and time Tl, the flyback power converter 200 can transfer energy on the primary side winding 210 of the flyback power converter 200 to the secondary side SEC of the flyback power converter 200.

[0049] As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. Figure 4 5 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. Figure 5 Figure 5 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. Figure 4 5 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. Figure 5 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A.

[0050] Figure 4 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. 6 Figure 6 As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A.

[0051] As shown in FIG. 2B, between time Tl and a time T2, although the primary controller 202 does not activate the gate control signal VGSSW to the power switch 206, the current IDSSW on the primary side PRI can flow through the parasitic diode (not shown in FIG. 2A) of the power switch 206, so the voltage VDSSW across the power switch 206 gradually decreases to zero and the voltage VDSSR across the synchronous switch 208 starts to gradually increase until (VIN / N) + VOUT, where the direction of the current IDSSW on the primary side PRI is referred to FIG. 2A. Figure 4 7 ​​​​​​As shown, between time T3 and a time T4, the secondary controller 204 activates a gate control signal VGSSR to the synchronous switch 208, at which time the current IDSSR of the secondary side SEC can flow through the synchronous switch 208, so the cross voltage VDSSR of the synchronous switch 208 is zero and the cross voltage VDSSW of the power switch 206 is VIN+(N*VOUT), where the direction of the current IDSSR of the secondary side SEC is referred to Figure 7 . In addition, because the primary side PRI of the flyback power converter 200 and the secondary side SEC of the flyback power converter 200 are not operated at the same time, at this time the primary controller 202 deactivates the gate control signal VGSSW. In addition, between time T3 and time T4, the flyback power converter 200 can transfer the energy on the secondary side winding 212 of the flyback power converter 200 to a load (not shown in Figure 7 ) coupled to the secondary side SEC of the flyback power converter 200.

[0052] In addition, the switching loss PSW and the conduction loss PCON of the power switch 206 are determined by equations (2) and (3), respectively:

[0053]

[0054] PCON = RDSSW(ON) x IDSSW(RMS) 2 (3)

[0055] As shown in equation (2), COSS is the parasitic capacitance of the power switch 206, VDSSW is VINMAX-N*(VOUT+VF) in the quasi-resonant mode, VINMAX is the maximum value of the input voltage VIN, VF is the cross voltage of the parasitic diode of the synchronous switch 208, VDSSW is zero in the zero voltage switching mode, and FSW is the operating frequency of the flyback power converter 200. In addition, because VDSSW is zero in the zero voltage switching mode, it can be known from equation (2) that the switching loss PSW of the power switch 206 is zero in the zero voltage switching mode. In addition, as shown in equation (3), RDSSW is the on-resistance of the power switch 206, and IDSSW(RMS) is the root mean square value of the current IDSSW of the primary side PRI.

[0056] In addition, the switching loss PSWSRAUX and the conduction loss PCONSRAUX of the synchronous switch 208 in the zero voltage switching mode are determined by equations (4) and (5), respectively:

[0057]

[0058]

[0059] As shown in equation (4), COSSSR is the parasitic capacitance of the synchronous switch 208, and the cross voltage VDSSR is between 0 and 2*VOUT. In addition, as shown in equation (5), RDSSR(ON) is the on-resistance of the synchronous switch 208, IDSSRMAX is the maximum value of the current IDSSR at the secondary side SEC, and DAUX is the on-time of the synchronous switch 208.

[0060] As shown in equation (2), the loss PZVS of the flyback power converter 200 in the zero voltage switching mode can be calculated according to the input voltage VIN, the on-time of the synchronous switch 208 DAUX, the cross voltage VDSSR, the on-resistance of the synchronous switch 208 RDSSR(ON), the maximum value of the current IDSSR at the secondary side SEC IDSSRMAX, and the parasitic capacitance of the synchronous switch 208 COSSSR. Figure 8 As shown in equation (2), the loss PZVS of the flyback power converter 200 in the zero voltage switching mode can be calculated according to the input voltage VIN, the on-time of the synchronous switch 208 DAUX, the cross voltage VDSSR, the on-resistance of the synchronous switch 208 RDSSR(ON), the maximum value of the current IDSSR at the secondary side SEC IDSSRMAX, and the parasitic capacitance of the synchronous switch 208 COSSSR.

[0061] As shown in equation (2), the loss PZVS of the flyback power converter 200 in the zero voltage switching mode can be calculated according to the input voltage VIN, the on-time of the synchronous switch 208 DAUX, the cross voltage VDSSR, the on-resistance of the synchronous switch 208 RDSSR(ON), the maximum value of the current IDSSR at the secondary side SEC IDSSRMAX, and the parasitic capacitance of the synchronous switch 208 COSSSR. Figure 9 As shown in equation (2), the loss PZVS of the flyback power converter 200 in the zero voltage switching mode can be calculated according to the input voltage VIN, the on-time of the synchronous switch 208 DAUX, the cross voltage VDSSR, the on-resistance of the synchronous switch 208 RDSSR(ON), the maximum value of the current IDSSR at the secondary side SEC IDSSRMAX, and the parasitic capacitance of the synchronous switch 208 COSSSR.

[0062] In step 104, if the inductance-capacitance resonance valley number LCRVN is greater than the predetermined number, it means that the load coupled to the secondary side SEC of the flyback power converter 200 is a light load. In step 106, the primary controller 202 can derive the operating frequency of the flyback power converter 200 according to the on-time TON, the off-time TDIS, and the inductance-capacitance resonance time corresponding to the inductance-capacitance resonance valley number LCRVN. Therefore, in steps 104 to 108, the primary controller 202 can control the flyback power converter 200 to operate in the quasi-resonant mode when the inductance-capitance resonance valley number LCRVN is greater than the predetermined number, the operating frequency is less than the predetermined frequency PF (which also means that the load coupled to the secondary side SEC of the flyback power converter 200 is a light load), and the input voltage VIN is less than the predetermined voltage PV, so that the efficiency of the flyback power converter 200 is better. Figure 8 , 9 It is obvious that the primary controller 202 can control the flyback power converter 200 to operate in the quasi-resonant mode when the inductance-capitance resonance valley number LCRVN is greater than the predetermined number, the operating frequency is less than the predetermined frequency PF (which also means that the load coupled to the secondary side SEC of the flyback power converter 200 is a light load), and the input voltage VIN is less than the predetermined voltage PV, so that the efficiency of the flyback power converter 200 is better.

[0063] In addition, in steps 104 to 108, the primary controller 202 controls the operation of the flyback power converter 200 in the quasi-resonant mode when the number of inductor-capacitor resonance valleys LCRVN is greater than the predetermined number (meaning that the load coupled to the secondary side SEC of the flyback power converter 200 is a light load), or the operation frequency of the flyback power converter 200 is less than the predetermined frequency PF (also meaning that the load coupled to the secondary side SEC of the flyback power converter 200 is a light load), or the input voltage VIN is less than the predetermined voltage PV. Figure 8 9 It is also obvious that when the number of inductor-capacitor resonance valleys LCRVN is less than the predetermined number (meaning that the load coupled to the secondary side SEC of the flyback power converter 200 is a heavy load), or the operation frequency of the flyback power converter 200 is greater than the predetermined frequency PF (also meaning that the load coupled to the secondary side SEC of the flyback power converter 200 is a heavy load), or the input voltage VIN is greater than the predetermined voltage PV, the primary controller 202 can control the flyback power converter 200 to operate in the zero-voltage switching mode so as to make the efficiency of the flyback power converter 200 better.

[0064] In addition, in another embodiment of the present application, the operation method of the flyback power converter 200 is also applicable to an active clamp flyback power converter 1000 (as shown in FIG. 10), wherein a photo-coupler 1002 separates the primary side PRI of the active clamp flyback power converter 1000 from the secondary side SEC of the active clamp flyback power converter 1000, as shown in FIG. 11. In addition, the function of a switch 1004 can be analogous to the function of the synchronous switch 208 of the flyback power converter 200, and the function of a clamp capacitor 1006 can be analogous to the function of the clamp circuit of the flyback power converter 200, as shown in FIG. 12. In addition, the operation principle of the active clamp flyback power converter 1000 is well known to those skilled in the art, and will not be described herein. Figure 1 Figure 10 Figure 10 Figure 10

[0065] In summary, the operation method of the flyback power converter disclosed in the present application controls the flyback power converter to switch between the quasi-resonant mode and the zero-voltage switching mode according to the on-time of the power switch of the primary side of the flyback power converter detected by the voltage detection pin of the primary controller, the on-time of the synchronous switch of the secondary side of the flyback power converter detected by the feedback pin of the primary controller, the number of inductor-capacitor resonance valleys when the flyback power converter operates in the discontinuous conduction mode detected by the feedback pin of the primary controller, and the input voltage to the flyback power converter detected by the high-voltage detection pin of the primary controller. Therefore, compared to the prior art, because the present application can control the flyback power converter to switch between the quasi-resonant mode and the zero-voltage switching mode, the efficiency of the flyback power converter can be made better.

[0066] ​​​​​The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A method of operating a flyback power converter, characterized by comprising: a voltage detection pin to detect a conduction time of a power switch on a primary side of the flyback power converter, a feedback pin to detect a conduction time of a synchronous switch on a secondary side of the flyback power converter, the feedback pin to detect a number of inductor-capacitor resonance valley when the flyback power converter operates in a discontinuous conduction mode, and a high voltage detection pin to detect an input voltage input to the flyback power converter; and when the number of inductor-capacitor resonance valley is greater than a predetermined number, an operating frequency of the flyback power converter is less than a predetermined frequency, and the input voltage is less than a predetermined voltage, a controller applied to the flyback power converter causes the flyback power converter to operate in a quasi-resonant mode.

2. The operating method of claim 1, wherein when the number of inductor-capacitor resonance valley is less than the predetermined number, the controller causes the flyback power converter to operate in a zero voltage switching mode. 3.The operating method of claim 1, wherein when the operating frequency of the flyback power converter is greater than the predetermined frequency, the controller causes the flyback power converter to operate in a zero voltage switching mode.

4. The operating method of claim 1, wherein when the input voltage is greater than the predetermined voltage, the controller causes the flyback power converter to operate in a zero voltage switching mode. 5.The operating method of claim 1, wherein the flyback power converter is a secondary side regulated flyback power converter.

6. The operating method of claim 1, wherein the flyback power converter is an active clamp flyback power converter.

7. The operating method of claim 1, wherein the controller has 6 pins, and the 6 pins comprise at least the voltage detection pin, the feedback pin, and the high voltage detection pin.

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