Capacitively coupled floating gate driver
High-performance low-power isolated bootstrapped gate drive apparatus and methods are disclosed for driving high-side and floating transistors. The gate drivers use edge-triggered capacitive-coupled inputs. The gate drivers may include detection and delay circuitry to facilitate zero-voltage-switching of the high side or floating transistor and providing more robust rejection of false triggering. A capacitively coupled differential input edge triggered gate driver provides exceptional immunity to false triggering. The gate drivers may be used in transformer coupled drive circuits using transformers that need only support coupled pulses wide enough to be recognized as an edge by the input circuit.
1. A method comprising:
providing a gate driver having an input connection, an output connection for driving a control terminal of a switch, a power connection for receiving power to operate the gate driver, and a return connection for providing a return path for the power connection and the output connection;
sensing relative to the return connection an input signal;
sensing a variation between a first node internal to the gate driver and a reference signal external to the gate driver;
executing a decision based upon the input signal and the variation whether to turn the switch ON;
driving the output connection relative to the return connection to turn the switch ON.
2. The method of claim 1 wherein the variation further comprises a rate of change of voltage between the first node and the external reference signal.
3. The method of claim 2 wherein executing the decision further comprises waiting until the rate of change is less than a predetermined minimum.
4. The method of claim 1 further comprising providing a DC blocking capacitor connected in series with the input connection.
5. The method of claim 4 further comprising providing a control circuit having an output connected in series with the DC blocking capacitor and referenced to the reference signal, wherein the control circuit is adapted to provide a first control signal to turn the switch ON and a second control signal to turn the switch OFF.
6. The method of claim 5 wherein the first node is connected to the input connection and
the sensing a variation further comprises providing a bias source connected to the first node, and the variation comprises a voltage or current at the first node.
7. The method of claim 5 wherein the variation further comprises a rate of change of voltage between the first node and the reference signal.
8. The method of claim 7 wherein executing the decision further comprises waiting for the rate of change to fall below a predetermined minimum before turning the switch ON.
9. The method of claim 1 wherein the switch comprises a MOSFET and further comprising:
providing the MOSFET having a gate connected to the output connection and having a source or a drain connected to the return connection.
10. The method of claim 9 wherein the reference signal is a ground reference and the return connection floats with respect to the ground reference.
11. The method of claim 1 wherein the input signal comprises a transition having a polarity, the sensing an input signal comprises sensing the transition in the input signal, and the decision is based upon the transition in the input signal.
12. The method of claim 11 wherein
turning the switch from OFF to ON causes a first voltage transition at the return connection and turning the switch from ON to OFF causes a second voltage transition at the return connection;
executing the decision comprises sensing a first transition polarity to turn the switch ON and a second transition polarity to turn the switch OFF; and
further comprising setting the first transition polarity to the opposite of the polarity of the first voltage transition and the second transition polarity to the opposite of the polarity of the second voltage transition.
13. The method of claim 1 wherein
the input connection comprises a first input connection and a second input connection;
the sensing an input signal further comprises sensing a first input signal and a second input signal respectively at the first and second input connections relative to the return connection, the first and second input signals comprising a transition; and
the decision is based upon sensing a first transition in the first input signal and a second transition in the second input signal, the second transition having a polarity opposite that of the first transition.
14. The method of claim 1 further comprising providing a DC blocking capacitance between the first node and the reference signal and the sensing a variation further comprises sensing a signal at the first node.
15. The method of claim 1 wherein the sensing a variation further comprises:
providing a DC blocking capacitance connected between the first node and the reference signal;
providing a bias source connected to the first node; and
sensing the voltage or current at the first node.
16. The method of claim 1 wherein executing the decision further comprises providing a predetermined delay before turning the switch ON.
17. The method of claim 16 further comprising providing a mechanism for selectively adjusting the predetermined delay.
18. The method of claim 16 further comprising providing a mechanism for selectively disabling the predetermined delay.
19. The method of claim 10 further comprising:
providing a control circuit having an output referenced to the ground reference, and adapted to provide a first control signal to turn the switch ON and a second control signal to turn the switch OFF;
providing transformer coupling between the output of the control circuit and the input connection; and
providing a DC blocking capacitor connected in series between the transformer coupling and the input connection.
20. Apparatus comprising:
a gate driver having internal circuitry connected to an input connection, an output connection, a power connection, and a return connection,
the internal circuitry being adapted to
(i) sense relative to the return connection an input signal,
(ii) sense a variation between a first node internal to the gate driver and a reference signal external to the gate driver,
(iii) drive the output connection relative to the return connection for driving a control terminal of a switch,
(iv) execute a decision whether to turn the switch ON based upon the input signal and the variation, and
(v) receive operating power via the power connection and the return connection.
21. The apparatus of claim 20 wherein the variation comprises a rate of change of voltage between the first node and the external reference signal.
22. The apparatus of claim 21 wherein executing the decision further comprises waiting until the rate of change is less than a predetermined minimum.
23. The apparatus of claim 20 further comprising a DC blocking capacitor connected in series with the input connection.
24. The apparatus of claim 23 further comprising:
a control circuit having an output referenced to the reference signal, the control circuit being adapted to provide a first control signal to turn the switch ON and a second control signal to turn the switch OFF;
the output of the control circuit being connected in series with the DC blocking capacitor.
25. The apparatus of claim 24 wherein the internal circuitry further comprises a bias source connected to the first node, wherein the variation comprises a variation in voltage or current at the first node, and wherein the first node is connected to the input connection.
26. The apparatus of claim 24 wherein the variation comprises a rate of change of voltage between the first node and the reference signal.
27. The apparatus of claim 26 wherein executing the decision further comprises waiting for the rate of change to fall below a predetermined minimum before turning the switch ON.
28. The apparatus of claim 20 wherein the switch comprises a MOSFET and further comprising the MOSFET having a gate connected to the output connection and having a source or a drain connected to the return connection.
29. The apparatus of claim 28 wherein the reference signal is a ground reference and the return connection floats with respect to the ground reference.
30. The apparatus of claim 20 wherein the input signal comprises a transition having a polarity, the internal circuitry is adapted to sense the transition in the input signal, and the decision is based upon the transition in the input signal.
31. The apparatus of claim 30 wherein
turning the switch from OFF to ON causes a first voltage transition at the return connection and turning the switch from ON to OFF causes a second voltage transition at the return connection;
executing the decision is based upon sensing a first transition polarity to turn the switch ON and a second transition polarity to turn the switch OFF; and
wherein the first transition polarity is opposite of the polarity of the first voltage transition and the second transition polarity is opposite of the polarity of the second voltage transition.
32. The apparatus of claim 20 wherein
the input connection comprises a first input connection and a second input connection;
the input signal further comprises a first input signal and a second input signal respectively at the first and second input connections relative to the return connection, the first and second input signals comprising a transition; and
the decision is based upon sensing a first transition in the first input signal and a second transition in the second input signal, the second transition having a polarity opposite that of the first transition.
33. The apparatus of claim 20 further comprising a DC blocking capacitance connected between the first node and the reference signal and wherein the variation further comprises a signal at the first node.
34. The apparatus of claim 20 further comprising:
a DC blocking capacitance connected between the first node and the reference signal; and
a bias source connected to the first node; and
wherein the variation comprises a voltage or current at the first node.
35. The apparatus of claim 20 wherein the decision further comprises providing a predetermined delay before turning the switch ON.
36. The apparatus of claim 35 further comprising a mechanism for selectively adjusting the predetermined delay.
37. The apparatus of claim 35 further comprising a mechanism for selectively disabling the predetermined delay.
38. The apparatus of claim 29 further comprising:
a control circuit having an output referenced to the ground reference for providing a first control signal to turn the switch ON and a second control signal to turn the switch OFF;
a transformer connected between the output of the control circuit and the input connection; and
a DC blocking capacitor connected in series between the transformer and the input connection.