Synchronous rectifier applied to a power converter and operation method thereof

A synchronous rectifier applied to a power converter includes a power supply module, a control module, and a gate driving unit. The power supply module is used for generating a supply current according to an induced voltage generated from a secondary side of the power converter, wherein the supply current is used for establishing a supply voltage, and the induced voltage corresponds to a control signal of a power switch of a primary side of the power converter. The control module is coupled to the power supply module for turning on or turning off the power supply module according to the supply voltage. The gate driving unit is coupled to the power supply module for generating a gate control signal controlling turning-on and turning-off of a synchronous switch of the secondary side of the power converter, wherein the supply voltage is used for driving the gate driving unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a synchronous rectifier applied to a power converter and an operation method thereof, and particularly to a synchronous rectifier and an operation method thereof that can generate a supply voltage independent of an output voltage of a secondary side of the power converter and do not need an auxiliary winding of a primary side of the power converter.

2. Description of the Prior Art

When an alternating current (AC)/direct current (DC) power converter is applied to a charge system, sometimes an output voltage of a secondary side of the AC/DC power converter is decreased to very low potential because the charge system needs to full charge an electronic product electrically connected to the charge system. When the output voltage of the secondary side of the AC/DC power converter is decreased to very low potential, if a synchronous rectifier of the secondary side of the AC/DC power converter needs the output voltage to act as a supply voltage, meanwhile the synchronous rectifier cannot operate normally because the output voltage is decreased to very low potential, resulting in conversion efficiency of the AC/DC power converter being reduced and the AC/DC power converter having serious heating problem.

The prior art utilizes an auxiliary voltage generated by an auxiliary winding of a primary side of the AC/DC power converter to act as the supply voltage of the synchronous rectifier, but the auxiliary winding will increase cost of the AC/DC power converter and design complexity. Therefore, for a designer of the synchronous rectifier, how to improve the above mentioned disadvantages of the prior art becomes an important issue.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a synchronous rectifier applied to a power converter. The synchronous rectifier includes a power supply module, a control module, and a gate driving unit. The power supply module is used for generating a supply current according to an induced voltage generated from a secondary side of the power converter, wherein the supply current is used for establishing a supply voltage, and the induced voltage corresponds to a control signal of a power switch of a primary side of the power converter. The control module is coupled to the power supply module for turning on or turning off the power supply module according to the supply voltage. The gate driving unit is coupled to the power supply module for generating a gate control signal controlling turning-on and turning-off of a synchronous switch of the secondary side of the power converter according to the induced voltage, wherein the supply voltage is used for driving the gate driving unit.

Another embodiment of the present invention provides an operation method of a synchronous rectifier applied to a power converter, wherein the synchronous rectifier includes a power supply module, a control module, and a gate driving unit. The operation method includes the power supply module generating a supply current according to an induced voltage generated from a secondary side of the power converter, wherein the supply current is used for establishing a supply voltage, and the induced voltage corresponds to a control signal of a power switch of a primary side of the power converter; and the control module turning on or turning off the power supply module according to the supply voltage.

The present invention provides a synchronous rectifier applied to a power converter and an operation method thereof. The synchronous rectifier and the operation method utilize a power supply module to establish a supply voltage of a gate driving unit according to an induced voltage generated from a secondary side of the power converter, wherein the induced voltage generated from the secondary side of the power converter corresponds to a control signal of a power switch of a primary side of the power converter, so the supply voltage of the gate driving unit is independent of an output voltage of the secondary side of the power converter. Therefore, compared to the prior art, because the supply voltage of the gate driving unit is independent of the output voltage of the secondary side of the power converter, the gate driving unit of the present invention can still operate normally when the output voltage of the secondary side of the power converter is reduced to very low potential. In addition, because the present invention does not need an auxiliary voltage generated by an auxiliary winding of the primary side of the power converter to act as the supply voltage of the gate driving unit, the present invention has lower cost and simpler design.

DETAILED DESCRIPTION

Please refer toFIG. 1.FIG. 1is a diagram illustrating a synchronous rectifier200applied to a secondary side SEC of a power converter100according to a first embodiment of the present invention, wherein a primary side PRI of the power converter100only shows a primary winding102and a power switch104inFIG. 1, and the power converter100is an alternating current/direct current power converter. As shown inFIG. 1, the synchronous rectifier200includes a power supply module202, a control module204, and a gate driving unit206, the power supply module202includes a high voltage switch2022, a voltage limit unit2024, a gate clamping unit2026, and a diode2028, and the control module204includes a switch2042and a comparison unit2044. As shown inFIG. 1, the voltage limit unit2024is coupled between a gate terminal of the high voltage switch2022and a drain terminal of the high voltage switch2022, the gate clamping unit2026is coupled between a source terminal of the high voltage switch2022and the gate terminal of the high voltage switch2022, and the diode2028is coupled between the source terminal of the high voltage switch2022and a pin208of the synchronous rectifier200, wherein the gate clamping unit2026is a clamp circuit. The switch2042is coupled between the gate terminal of the high voltage switch2022and ground GND of the power converter100, and the comparison unit2044is coupled to the switch2042and the pin208, wherein the switch2042is coupled to the ground GND of the power converter100through a pin210of the synchronous rectifier200.

As shown inFIG. 1, when the power switch104of the primary side PRI of the power converter100is turned on according to a control signal CS, a secondary winding106of the secondary side SEC of the power converter100can generate an induced voltage SRVDS (corresponding to the control signal CS of the power switch104) according to a current IPRI flowing through the primary side PRI of the power converter100. As shown inFIG. 1, when the switch2042is turned off, the high voltage switch2022can receive the induced voltage SRVDS through a pin212of the synchronous rectifier200, and generate a supply current SC according to the induced voltage SRVDS, wherein the supply current SC is used for charging a capacitor214to establish a supply voltage VCC through the pin208of the synchronous rectifier200. Meanwhile, because high potential of the induced voltage SRCDS can damage the gate terminal of the high voltage switch2022, the voltage limit unit2024can limit the induced voltage SRCDS to a predetermined voltage PV to protect the gate terminal of the high voltage switch2022, wherein the predetermined voltage PV is lower than the induced voltage SRVDS, and the voltage limit unit2024is a Junction Field Effect Transistor (JFET). But, the present invention is not limited to the voltage limit unit2024being a JFET. The gate clamping unit2026includes a transistor20262for clamping a voltage between the gate terminal of the high voltage switch2022and the source terminal of the high voltage switch2022. That is to say, the gate clamping unit2026can utilize the transistor20262to clamp the voltage between the gate terminal of the high voltage switch2022and the source terminal of the high voltage switch2022to protect the high voltage switch2022to make the high voltage switch2022operate normally. But, the present invention is not limited to the gate clamping unit2026including the transistor20262, that is, the gate clamping unit2026can include at least one transistor. The diode2028is used for preventing the supply voltage VCC from reversing to the gate clamping unit2026and the high voltage switch2022when the high voltage switch2022is turned off.

Please refer toFIGS. 1, 2. When the supply voltage VCC is greater than an upper limit UL, the comparison unit2044can make the switch2042be turned on, resulting in the high voltage switch2022being turned off (because potential of the gate terminal of the high voltage switch2022is pulled down to the ground GND). Meanwhile, the supply voltage VCC of the capacitor214is gradually decreased with a load (not shown inFIG. 1) coupled to the secondary side SEC of the power converter100; and when the supply voltage VCC is decreased to be less than a lower limit LL, the comparison unit2044can make the switch2042be turned off, resulting in the high voltage switch2022being turned on again. Meanwhile, the power supply module202can utilize the supply current SC to charge the capacitor214again to make the supply voltage VCC be increased. Therefore, as shown inFIG. 2, the supply voltage VCC is changed between the upper limit UL and the lower limit LL. In addition, in another embodiment of the present invention, the comparison unit2044is a hysteresis comparator, so the comparison unit2044can utilize the supply voltage VCC, the upper limit UL, and a hysteresis range of the comparison unit2044to make the supply voltage VCC be changed between the upper limit UL and the lower limit LL.

As shown inFIG. 1, the gate driving unit206can receive the induced voltage SRVDS from a drain terminal of the synchronous switch108of the secondary side SEC of the power converter100through the pin212of the synchronous rectifier200, and generate a gate control signal GCS controlling turning-on and turning-off of the synchronous switch108of the secondary side SEC of the power converter100according to the induced voltage SRVDS, wherein the gate control signal GCS can be transmitted to a gate terminal of the synchronous switch108through a pin216of the synchronous rectifier200, and the supply voltage VCC is used for driving the gate driving unit206. In addition, because the power converter100is a flyback power converter, the gate control signal GCS can make the primary side PRI of the power converter100and the secondary side SEC of the power converter100be not simultaneously turned on. As shown inFIG. 3, the gate control signal GCS and the control signal CS are not overlapped each other because of a dead time DT, so the gate control signal GCS can prevent the primary side PRI of the power converter100and the secondary side SEC of the power converter100from being simultaneously turned on. In addition, in another embodiment of the present invention, the supply voltage VCC is further used for driving a monitor unit applied to the secondary side SEC of the power converter100or other circuits needing the supply voltage VCC (wherein the monitor unit and the other circuits are not shown inFIG. 1), wherein the monitor unit can be used for monitoring timings of the gate control signal GCS and the control signal CS.

Please refer toFIG. 4.FIG. 4is a diagram illustrating a synchronous rectifier400applied to the secondary side SEC of the power converter100according to a second embodiment of the present invention. As shown inFIG. 4, a difference between the synchronous rectifier400and the synchronous rectifier200is that a gate driving unit206of the synchronous rectifier400is further driven by an output voltage VOUT of the secondary side SEC of the power converter100, wherein the output voltage VOUT charges the capacitor214through a rectifier218. In addition, subsequent operational principles of the synchronous rectifier400are the same as those of the synchronous rectifier200, so further description thereof is omitted for simplicity.

Please refer toFIGS. 1-3andFIG. 5.FIG. 5is a flowchart illustrating an operation method of a synchronous rectifier applied to a power converter according to a third embodiment of the present invention. The operation method inFIG. 5is illustrated using the power converter100and the synchronous rectifier200inFIG. 1. Detailed steps are as follows:

Step502: The power supply module202generates the supply current SC to establish the supply voltage VCC according to the induced voltage SRVDS generated from the secondary side SEC of the power converter100.

Step504: If the supply voltage VCC is greater than upper limit UL; if yes, go to Step506; if no, go to Step502;

Step506: The control module204turns off the power supply module202.

Step508: If the supply voltage VCC is less than the lower limit LL; if yes, go to Step510; if no, go to Step506.

Step510: The control module204turns on the power supply module202, go to Step502.

In Step502, as shown inFIG. 1, when the power switch104of the primary side PRI of the power converter100is turned on according to the control signal CS, the secondary winding106of the secondary side SEC of the power converter100can generate the induced voltage SRVDS (corresponding to the control signal CS of the power switch104) according to the current IPRI flowing through the primary side PRI of the power converter100. As shown inFIG. 1, when the switch2042of the control module204is turned off, the high voltage switch2022of the power supply module202can receive the induced voltage SRVDS through the pin212of the synchronous rectifier200, and generate the supply current SC according to the induced voltage SRVDS, wherein the supply current SC is used for charging the capacitor214to establish the supply voltage VCC through the pin208of the synchronous rectifier200.

In Step506, as shown inFIGS. 1, 2, when the supply voltage VCC is greater than the upper limit UL, the comparison unit2044of the control module204can make the switch2042be turned on, resulting in the high voltage switch2022being turned off (because the potential of the gate terminal of the high voltage switch2022is pulled down to the ground GND). Meanwhile, the supply voltage VCC of the capacitor214is gradually decreased with the load (not shown inFIG. 1) coupled to the secondary side SEC of the power converter100; in Step510, when the supply voltage VCC is decreased to be less than the lower limit LL, the comparison unit2044can make the switch2042be turned off, resulting in the high voltage switch2022being turned on again. Meanwhile, the power supply module202can utilize the supply current SC to charge the capacitor214again to make the supply voltage VCC be increased. Therefore, as shown inFIG. 2, the supply voltage VCC is changed between the upper limit UL and the lower limit LL.

As shown inFIG. 1, because the supply voltage VCC can drive the gate driving unit206, the gate driving unit206can generate the gate control signal GCS controlling turning-on and turning-off of the synchronous switch108of the secondary side SEC of the power converter100according to the induced voltage SRVDS, wherein the gate control signal GCS can make the primary side PRI of the power converter100and the secondary side SEC of the power converter100be not simultaneously turned on (as shown inFIG. 3, the gate control signal GCS and the control signal CS are not overlapped each other because of the dead time DT, so the gate control signal GCS can prevent the primary side PRI of the power converter100and the secondary side SEC of the power converter100from being simultaneously turned on).

To sum up, the synchronous rectifier applied to a power converter and the operation method thereof utilize the power supply module to establish the supply voltage of the gate driving unit according to the induced voltage generated from the secondary side of the power converter, wherein the induced voltage generated from the secondary side of the power converter corresponds to the control signal of the power switch of the primary side of the power converter, so the supply voltage of the gate driving unit is independent of the output voltage of the secondary side of the power converter. Therefore, compared to the prior art, because the supply voltage of the gate driving unit is independent of the output voltage of the secondary side of the power converter, the gate driving unit of the present invention can still operate normally when the output voltage of the secondary side of the power converter is reduced to very low potential. In addition, because the present invention does not need an auxiliary voltage generated by an auxiliary winding of the primary side of the power converter to act as the supply voltage of the gate driving unit, the present invention has lower cost and simpler design.