Unidirectional switch circuit
A switch circuit for coupling two circuit terminals together is disclosed. The switch circuit includes a double-base bipolar junction transistor and a field-effect transistor coupled, in series, between a first terminal and a second terminal. Various driver circuits may be employed to activate, in response to an activation of a switch signal, the field-effect transistor, and couple one or both of the base terminals of the double-base bipolar junction transistor to voltage sources to initiate base currents to reduce the channel resistance of the double-base bipolar junction transistor.
1 . An apparatus, comprising:
a switch device coupled between a first terminal and a second terminal, wherein the switch device includes a double-base bipolar junction transistor and a first field-effect transistor; and
a driver circuit configured, in response to an activation of a switch signal, to:
when a first voltage of the first terminal is greater than a second voltage of the second terminal, activate the first field-effect transistor, and couple an upper-base of the double-base bipolar junction transistor to a voltage source to enable a forward current to flow from the first terminal to the second terminal; and
when the first voltage of the first terminal is less than the second voltage of the second terminal, couple the upper-base of the double-base bipolar junction transistor to the voltage source to enable a reverse current to flow from the second terminal to the first terminal through a body diode of the first field-effect transistor and the double-base bipolar junction transistor.
2 . The apparatus of claim 1 , wherein the driver circuit includes a second field-effect transistor coupled between the upper-base of the double-base bipolar junction transistor and the voltage source, wherein the voltage source is further coupled to the first terminal, and wherein to couple the upper-base of the double-base bipolar junction transistor to the voltage source, the driver circuit is further configured to activate the second field-effect transistor.
3 . The apparatus of claim 2 , wherein the driver circuit is further configured, in response to a deactivation of the switch signal, to:
decouple the upper-base of the double-base bipolar junction transistor from the voltage source; and
couple a lower-base of the double-base bipolar junction transistor to the second terminal.
4 . The apparatus of claim 3 , wherein the driver circuit is further configured, in response to the deactivation of the switch signal, to deactivate the first field-effect transistor in response to a determination that a particular time period has elapsed since the deactivation of the switch signal.
5 . The apparatus of claim 3 , wherein the driver circuit further includes a third field-effect transistor coupled between the lower-base of the double-base bipolar junction transistor and the second terminal, and wherein to couple the lower-base of the double-base bipolar junction transistor to the second terminal, the driver circuit is further configured to activate the third field-effect transistor.
6 . The apparatus of claim 1 , wherein the driver circuit is further configured, in response to the activation of the switch signal, to when the first voltage of the first terminal is less than the second voltage of the second terminal, activate the first field-effect transistor, wherein a first portion of the reverse current flows through the body diode of the first field-effect transistor and a second portion of the reverse current flows through the first field-effect transistor.
7 . A method, comprising:
receiving, by a switch circuit, a switch signal, wherein the switch circuit includes a double-base bipolar junction transistor and a first field-effect transistor coupled, in series, between a first terminal and a second terminal; and
in response to activating the switch signal:
when a first voltage of the first terminal is greater than a second voltage of the second terminal, activating the first field-effect transistor, and coupling an upper-base of the double-base bipolar junction transistor to a voltage source to enable a forward current to flow from the first terminal to the second terminal; and
when the first voltage of the first terminal is less than the second voltage of the second terminal, coupling the upper-base of the double-base bipolar junction transistor to the voltage source to enable a reverse current to flow from the second terminal to the first terminal through a body diode of the first field-effect transistor and the double-base bipolar junction transistor.
8 . The method of claim 7 , further comprising, in response to deactivating the switch signal:
decoupling the upper-base of the double-base bipolar junction transistor from the voltage source; and
coupling a lower-base of the double-base bipolar junction transistor to the second terminal.
9 . The method of claim 8 , further comprising, in response to determining a particular time period has elapsed since deactivating the switch signal, deactivating the first field-effect transistor.
10 . The method of claim 8 , wherein coupling the upper-base of the double-base bipolar junction transistor to the voltage source includes activating a second field-effect transistor coupled between the upper-base of the double-base bipolar junction transistor and the voltage source, and wherein the voltage source is further coupled to the first terminal.
11 . The method of claim 10 , wherein coupling the lower-base of the double-base bipolar junction transistor to the second terminal includes activating a third field-effect transistor coupled between the lower-base of the double-base bipolar junction transistor and the second terminal.
12 . The method of claim 7 , wherein a lower-base of the double-base bipolar junction transistor is electrically floating, and wherein the method further includes, in response to deactivating the switch signal:
decoupling the upper-base of the double-base bipolar junction transistor from the voltage source; and
deactivating the first field-effect transistor in response to determining a particular time period has elapsed since the switch signal was deactivated.
13 . The method of claim 7 , further comprising when the first voltage of the first terminal is less than the second voltage of the second terminal, activating the first field-effect transistor, wherein a first portion of the reverse current flows through the body diode of the first field-effect transistor and a second portion of the reverse current flows through the first field-effect transistor.
14 . An apparatus, comprising:
a switch device coupled between a first terminal and a second terminal, wherein the switch device includes a double-base bipolar junction transistor and a first field-effect transistor; and
a driver circuit configured, in response to an activation of a switch signal, to:
when a first voltage of the first terminal is greater than a second voltage of the second terminal, activate the first field-effect transistor, and couple a lower-base of the double-base bipolar junction transistor to a voltage source to enable a forward current from the first terminal to the second terminal; and
when the first voltage of the first terminal is less than the second voltage of the second terminal, couple the lower-base of the double-base bipolar junction transistor to the voltage source to enable a reverse current to flow from the second terminal to the first terminal through a body diode of the first field-effect transistor.
15 . The apparatus of claim 14 , wherein the driver circuit includes a second field-effect transistor coupled between the lower-base of the double-base bipolar junction transistor and the voltage source, wherein the voltage source is further coupled to the second terminal, and wherein to couple the lower-base of the double-base bipolar junction transistor to the voltage source, the driver circuit is further configured to activate the second field-effect transistor.
16 . The apparatus of claim 15 , wherein the driver circuit is further configured, in response to a deactivation of the switch signal, to:
decouple the lower-base of the double-base bipolar junction transistor from the voltage source; and
couple the lower-base of the double-base bipolar junction transistor to the second terminal.
17 . The apparatus of claim 16 , wherein the driver circuit further include a third field-effect transistor coupled between the lower-base of the double-base bipolar junction transistor and the second terminal, and wherein to couple the lower-base of the double-base bipolar junction transistor, the driver circuit is further configured to activate the third field-effect transistor.
18 . The apparatus of claim 14 , wherein an upper-base of the double-base bipolar junction transistor is electrically floating.
19 . The apparatus of claim 14 , wherein an upper-base of the double-base bipolar junction transistor is coupled to the first terminal.
20 . The apparatus of claim 14 , wherein the voltage source is coupled to an isolated power supply circuit, and wherein the driver circuit includes a startup circuit configured, during a startup operation, transfer power from a lower collector-emitter of the double-base bipolar junction transistor to the isolated power supply circuit, wherein the first field-effect transistor is inactive, and wherein a third voltage of an upper collector-emitter of the double-base bipolar junction transistor is greater than a fourth voltage of the lower collector-emitter of the double-base bipolar junction transistor.