Synchronous rectifier circuit and power supply
In a power supply of a synchronous rectification type, the self-turn on phenomenon of MOSFET is suppressed without increase of the drive loss to thereby improve the power efficiency. In a synchronous rectifier circuit, a threshold value of a commutation MOSFET is made higher than that of a rectification MOSFET and particularly a threshold value of a commutation MOSFET 3 is made 0.5V or more higher than that of a rectification MOSFET 2 . The threshold value of the rectification MOSFET 2 is lower than 1.5V and the threshold of the commutation MOSFET 3 is higher than 2.0V.
1. A power supply of a synchronous rectification type including a DC input power supply, a first insulated gate type power semiconductor element having one main terminal connected to a high potential side of the DC input power supply and a second insulated gate type power semiconductor element having one main terminal connected to the other main terminal of the first insulated gate type power semiconductor element and the other main terminal connected to a low potential side of the DC input power supply, a coil having one terminal connected to the other main terminal of the first insulated gate type power semiconductor element, an output condenser having one terminal connected to the other terminal of the coil and the other terminal connected to the other main terminal of the second insulated gate type power semiconductor element, a load having one terminal connected to the other terminal of the coil and the other terminal connected to the other main terminal of the second insulated gate type power semiconductor element, and a control circuit for driving gates of the first and second insulated gate type power semiconductor elements, wherein an absolute value of a threshold voltage of said second insulated gate type power semiconductor element is higher than that of said first insulated gate type power semiconductor element.
2. A power supply according to claim 1 , wherein a DC voltage lower than a voltage of said DC input power supply is outputted.
3. A power supply of a synchronous rectification type including a DC input power supply, a rectification MOSFET having one main terminal connected to a positive potential side of the DC input power supply, a commutation MOSFET having one main terminal connected to the other main terminal of the rectification MOSFET and the other main terminal connected to a negative potential side of the DC input power supply, a choke coil having one terminal connected to the other main terminal of the rectification MOSFET, an output condenser having one terminal connected to the other terminal of the choke coil and the other terminal connected to the other main terminal of the commutation MOSFET, a load having one terminal connected to the other terminal of the choke coil and the other terminal connected to the other main terminal of the commutation MOSFET, and a control circuit for driving gates of the rectification and commutation MOSFETs, wherein an absolute value of a threshold voltage of said commutation MOSFET is higher than that of said rectification MOSFET.
4. A power supply according to claim 3 , wherein a DC voltage lower than a voltage of said DC input power supply is outputted.
5. A power supply according to claim 3 , wherein the absolute value of the threshold voltage of said commutation MOSFET is 0.5V or more higher than that of said rectification MOSFET.
6. A power supply according to claim 3 , wherein the absolute value of the threshold voltage of said commutation MOSFET is equal to or smaller than 1.5V and the absolute value of the threshold value of said commutation MOSFET is equal to or larger than 2.0V.
7. A power supply according to claim 3 , wherein a total of wiring inductance of a main circuit of said power supply is equal to or larger than 10 nH, the absolute value of the threshold voltage of said commutation MOSFET is equal to or smaller than 1.5V, the absolute value of the threshold voltage of said commutation MOSFET being equal to or larger than 2.5V.
8. A power supply of a synchronous rectification type including a DC input power supply, a rectification MOSFET having one main terminal connected to a high potential side of the DC input power supply, a commutation MOSFET having one main terminal connected to the other main terminal of the rectification MOSFET and the other main terminal connected to a low potential side of the DC input power supply, a coil having one terminal connected to the other main terminal of the rectification MOSFET, an output condenser having one terminal connected to the other terminal of the coil and the other terminal connected to the other main terminal of the commutation MOSFET, a load having one terminal connected to the other terminal of the coil and the other terminal connected to the other main terminal of the commutation MOSFET, and a control circuit for driving gates of the rectification and commutation MOSFETs, wherein an absolute value of a threshold voltage of said commutation MOSFET is higher than that of said rectification MOSFET and self-turn on loss of said commutation MOSFET is smaller than conduction loss of said commutation MOSFET.
9. A power supply according to claim 8 , wherein a DC voltage lower than a voltage of said DC input power supply is outputted.
10. A power supply according to claim 9 , wherein the absolute value of the threshold voltage of said commutation MOSFET is 0.5V or more higher than that of said rectification MOSFET.