Switch controller with validation circuit for improved noise immunity
A switch controller for controlling a power switch includes a signal transformer to galvanically isolate a primary side from a secondary side and receive and transfer a transition signal to transition the power switch to an on or off state between the primary side and the secondary side. The transition signal pulses to a first value to indicate the power switch transitions to the on state, to a second value to indicate the power switch transitions to the off state, and remains at a third value when there is no transition. A transmission circuit is coupled to a primary winding to control a switch to generate the transition signal. The switch switches a substantially low impedance onto the primary winding when there is no transition. A receiver circuit is coupled to a secondary winding to generate a drive signal to control the power switch in response to the transition signal.
1. A switch controller for controlling a power switch, comprising:
a signal transformer that is coupled to galvanically isolate a primary side of the switch controller from a secondary side of the switch controller and further coupled to receive and transfer a transition signal representative of transitioning the power switch to an on state or to an off state between the primary side and the secondary side, wherein the transition signal pulses to a first value to indicate the power switch transitions to the on state, pulses to a second value to indicate the power switch transitions to the off state, and remains at a third value when there is no transition and a substantially low impendence is switched onto a primary winding of the signal transformer, wherein a length of time for the pulses is a signal duration; and
a receiver circuit coupled to a secondary winding of the signal transformer, wherein the receiver circuit receives the transition signal and generates a drive signal to control the power switch in response to the transition signal, wherein the receiver circuit further comprises:
a validation circuit coupled to validate the received transition signal, wherein the validation circuit comprises:
a first comparator to compare a magnitude of the received transition signal with a magnitude threshold;
a timer to time a duration that the magnitude of the received transition signal exceeds the magnitude threshold; and
a second comparator to compare the timed duration with a threshold duration; and
a drive signal generator coupled to generate the drive signal in response to the validation circuit indicating that the received transition signal is valid, wherein the received transition signal is valid when the timed duration exceeds the threshold duration.
2. The switch controller of claim 1 , wherein the first value and the second value have substantially the same magnitude but opposite polarity.
3. The switch controller of claim 1 , wherein the third value is substantially zero.
4. The switch controller of claim 1 , wherein the transmission circuit further controls the switch such that a voltage across the primary winding of the signal transformer is substantially zero when the transition signal indicates there is no transition.
5. The switch controller of claim 1 , wherein the primary winding and the secondary winding are wound around the signal transformer, wherein the primary winding partially or fully covers the secondary winding.
6. The switch controller of claim 1 , wherein the threshold duration is less than the signal duration.
7. The switch controller of claim 6 , wherein the threshold duration is greater than 20% of the signal duration.
8. The switch controller of claim 6 , wherein the threshold duration is greater than 40% of the signal duration.
9. The switch controller of claim 6 , wherein the signal duration minus the threshold duration is less than 100 nanoseconds.
10. The switch controller of claim 6 , wherein the signal duration minus the threshold duration is less than 50 nanoseconds.
11. The switch controller of claim 6 , wherein the signal duration minus the threshold duration is less than 30 nanoseconds.
12. The switch controller of claim 1 , wherein the timer comprises:
a capacitor;
a current source to charge the capacitor when the magnitude of the received transition signal exceeds the magnitude threshold; and
a current sink to discharge the capacitor when the magnitude of the received transition signal does not exceed the magnitude threshold.
13. The switch controller of claim 1 , wherein the relatively low impedance is a short circuit.
14. The switch controller of claim 1 , wherein the relatively low impedance is a voltage source blocked by a bypass capacitor.
15. The switch controller of claim 1 , wherein the relatively low impedance is a capacitor in series with the winding.
16. The switch controller of claim 1 , wherein the power switch comprises an insulated gate bipolar transistor to transition between an off and on states in a time greater than 100 nanoseconds.
17. The switch controller of claim 1 , wherein the power switch comprises an insulated gate bipolar transistor to transition between an off and on states in a transition time, the transition time being greater than the measurement period of time.
18. The switch controller of claim 1 , further comprising:
a transmission circuit coupled to the primary winding of the signal transformer, wherein the transmission circuit is coupled to control a switch to generate the transition signal, wherein the switch switches the substantially low impedance onto the primary winding when the transition signal indicates there is no transition.
19. A switch controller for controlling a power switch, comprising:
a signal transformer that is coupled to galvanically isolate a primary side of the switch controller from a secondary side of the switch controller and further coupled to receive and a transition signal representative of transitioning the power switch to an on state or to an off state between the primary side and the secondary side, wherein the transition signal pulses to a first value to indicate the power switch transitions to the on state, pulses to a second value to indicate the power switch transitions to the off state, and remains at a third value when there is no transition;
a transmission circuit coupled to a primary winding of the signal transformer, wherein the transmission circuit is coupled to generate the transition signal, wherein the transmission circuit further applies a substantially low impedance onto the primary winding when the transition signal indicates there is no transition; and
a receiver circuit coupled to a secondary winding of the signal transformer, wherein the receiver circuit receives the transition signal and generates a drive signal to control the power switch in response to the transition signal, wherein the receiver circuit further comprises:
a validation circuit coupled to validate the received transition signal, wherein the validation circuit comprises:
a first comparator to compare a magnitude of the received transition signal with a magnitude threshold;
a timer to time a duration that the magnitude of the received transition signal exceeds the magnitude threshold; and
a second comparator to compare the timed duration with a threshold duration.
20. The switch controller of claim 19 , wherein the relatively low impedance is a short circuit.
21. The switch controller of claim 19 , wherein the power switch comprises an insulated gate bipolar transistor to transition between an off and on states in a time greater than 100 nanoseconds.
22. The switch controller of claim 19 , wherein the primary winding and the secondary winding are wound around the signal transformer, wherein the primary winding partially or fully covers the secondary winding.
23. The switch controller of claim 19 , wherein the first value and the second value have substantially the same magnitude but opposite polarity.
24. The switch controller of claim 19 , wherein the third value is substantially zero.
25. The switch controller of claim 19 , wherein the receiver circuit further comprises:
a drive signal generator coupled to generate the drive signal in response to the validation circuit indicating that the received transition signal is valid, wherein the received transition signal is valid when the timed duration exceeds the threshold duration.
26. The switch controller of claim 19 , wherein the timer comprises:
a capacitor;
a current source to charge the capacitor when the magnitude of the received transition signal exceeds the magnitude threshold; and
a current sink to discharge the capacitor when the magnitude of the received transition signal does not exceed the magnitude threshold.