Four quadrant MOSFET based switch
View Patent ↗An electronically controlled four quadrant MOSFET based switch in which a pair of drivers are provided in cooperation with a MOSFET. A first one of the drivers is arranged such that when current flow through the MOSFET is to be enabled responsive to a first condition of the control signal, the gate of the MOSFET is driven with an appropriate voltage, and when current flow through the MOSFET is to be disabled responsive to a second condition of the control signal, the gate is driven towards a limit voltage. A second one of the drivers is arranged such that when current flow through the MOSFET is to be enabled the body diode connection of the MOSFET is driven towards the potential of the MOSFET source, and when current flow through the MOSFET is to be disabled the body diode connection is driven towards the limit voltage.
1. An apparatus comprising:
a metal oxide semiconductor field effect transistor (MOSFET);
a first driver exhibiting an input responsive to a control signal and an output coupled to the gate of said MOSFET, said first driver arranged to apply a predetermined voltage to the gate of the MOSFET responsive to a first condition of the control signal, said predetermined voltage selected to enable current flow through the channel of the MOSFET, and to apply a limit voltage to the gate of the MOSFET responsive to a second condition of the control signal, said limit voltage consonant with the most extreme voltage experienced by the drain of said MOSFET when reverse biased in relation to the source of said MOSFET; and
a second driver exhibiting an input responsive to the control signal and an output coupled to the body connection of the MOSFET, said second driver arranged to apply a potential consonant with the potential of the source of the MOSFET to the body connection of said MOSFET responsive to the first condition of the control signal, and to apply the limit voltage to the body connection of said MOSFET responsive to the second condition of the control signal,
wherein said MOSFET, said first driver and said second driver constitute an electronically controlled switch.
2. An apparatus according to claim 1 , wherein said limit voltage is derived from the drain of said MOSFET.
3. An apparatus according to claim 1 , wherein said MOSFET is a p-channel MOSFET, and wherein said limit voltage is greater than or equal to a diode drop below the most positive voltage experienced by the drain of said p-channel MOSFET.
4. An apparatus according to claim 1 , wherein said MOSFET is an n-channel MOSFET, and wherein said limit voltage is less than or equal to a diode drop above the most negative voltage experienced by the drain of said n-channel MOSFET.
5. An apparatus according to claim 1 , comprising a plurality of said electronically controlled switches each having a unique control signal associated therewith, further comprising a transformer with a plurality of secondary windings, each of said secondary windings associated with a particular one of said electronically controlled switches.
6. An apparatus according to claim 5 , further comprising a control circuit arranged to output each of said unique control signals to each of said plurality of electronically controlled switches, said control circuitry further connected to receive an indication of the voltage output associated with each of said plurality of electronically controlled switches.
7. An apparatus according to claim 6 , wherein said control circuit is operative to set each of said unique control signals alternately to one of said first condition and said second condition responsive to said respective indication of voltage output, and wherein the drain to source voltage of the MOSFET of the electronically controlled switch may be reverse biased when said unique control signal is in said second condition, without appreciable current flow.
8. An apparatus according to claim 5 , wherein said transformer is a flyback transformer.
9. An apparatus according to claim 5 , wherein said transformer is a forward transformer.
10. A secondary side controller comprising:
a control circuit;
a transformer exhibiting a primary winding and a plurality of secondary windings magnetically coupled to said primary winding; and
a plurality of electronically controlled switches, each associated with a particular one of said secondary windings and each coupled to a respective control signal output of said control circuit, each of said electronically controlled switches comprising:
a metal oxide semiconductor field effect transistor (MOSFET);
a first driver exhibiting an input responsive to said respective control signal of said control circuit and an output coupled to the gate of said MOSFET, said first driver arranged to apply a predetermined voltage to the gate of the MOSFET responsive to a first condition of the respective control signal, said predetermined voltage selected to enable current flow through the channel of the MOSFET, and to apply a limit voltage to the gate of the MOSFET responsive to a second condition of the respective control signal, said limit voltage consonant with the most extreme voltage experienced by the drain of said MOSFET when reverse biased in relation to the source of said MOSFET; and
a second driver exhibiting an input responsive to the respective control signal and an output coupled to the body connection of the MOSFET, said second driver arranged to apply a potential consonant with the potential of the source of the MOSFET to the body connection of said MOSFET responsive to the first condition of the respective control signal, and to apply the limit voltage to the body connection of said MOSFET responsive to the second condition of the respective control signal,
wherein said control circuitry is further connected to receive an indication of the voltage output associated with each of said plurality of electronically controlled switches, and is operative to set each of said respective control signals alternately to one of said first condition and said second condition responsive to said respective indication of voltage output, and wherein the drain to source voltage of the MOSFET of the electronically controlled switch may be reverse biased when said unique control signal is in said second condition, without appreciable current flow.
11. A secondary side controller according to claim 10 , wherein said transformer is a flyback transformer.
12. A secondary side controller according to claim 10 , wherein said transformer is a forward transformer.
13. A method of electronically controlling a flow of current comprising:
providing a metal oxide semiconductor field effect transistor (MOSFET);
alternately applying a predetermined voltage to the gate of said provided MOSFET responsive to a first condition of a control signal, said predetermined voltage thereby enabling current flow through the channel of the MOSFET, and applying a limit voltage to the gate of the MOSFET responsive to a second condition of the control signal, said limit voltage consonant with the most extreme voltage experienced by the drain of said MOSFET when reverse biased in relation to the source of said MOSFET; and
applying a potential consonant with the potential of the source of the MOSFET to the body connection of said MOSFET responsive to the first condition of the control signal, and applying the limit voltage to the body connection of said MOSFET responsive to the second condition of the control signal.
14. A method according to claim 13 , further comprising deriving said limit voltage from the drain of said MOSFET.
15. A method according to claim 13 , wherein said provided MOSFET is a p-channel MOSFET, and wherein said limit voltage is greater than or equal to a diode drop below the most positive voltage experienced by the drain of said p-channel MOSFET.
16. A method according to claim 13 , wherein said MOSFET is an n-channel MOSFET, and wherein said limit voltage is less than or equal to a diode drop above the most negative voltage experienced by the drain of said n-channel MOSFET.
17. A method according to claim 13 , further comprising:
receiving an indication of an output voltage associated with said provided MOSFET; and
alternately setting said control signal to each of said first condition and said second condition responsive to said received indication of output voltage,
wherein the drain to source voltage of the provided MOSFET may be reverse biased when said control signal is in said second condition, without appreciable current flow.