Boost converter stage switch controller

1. A switch controller, comprising:

a set of one or more controller inputs, including:

a transformer input configured to receive a transformer signal from an electronic transformer; and

controller logic configured to:

detect edge transitions of the transformer signal;

generate a switch control signal for a switch configured to influence a current path of an inductor current of an inductor coupled to the electronic transformer; and

synchronize assertions of a switch control signal with the edge transitions.

2. The switch controller of claim 1 , wherein the inductor current flows through the switch as switch current and returns to the electronic transformer when the switch is closed.

3. The switch controller of claim 2 , wherein the inductor current is rectified and provided to a load when the switch is open.

4. The switch controller of claim 3 , wherein, following assertion of the switch control signal, the inductor current increases approximately linearly at a rate determined in accordance with a voltage of the transformer signal and an inductance of the inductor.

5. The switch controller of claim 4 , wherein the controller logic is configured to delay assertions of the switch control signal after edge transitions of the transformer signal by delay interval, wherein the delay interval results in a peak inductor current wherein the peak inductor current is greater than a minimum peak inductor current threshold and less than a maximum inductor current threshold.

6. The switch controller of claim 3 , wherein:

the controller inputs include a sense input configured to receive a sense signal indicative of the switch current; and

the controller logic is configured to control the switch control signal in further accordance with the sense signal.

7. The switch controller of claim 6 , wherein:

the controller inputs include a load input configured to receive a load signal indicative of a load voltage; and

the controller logic is configured to control the switch control signal in further accordance with the load signal.

8. The switch controller of claim 7 , the controller logic is configured to assert the switch control signal once per half-period of the transformer signal.

9. The switch controller of claim 8 , wherein the controller logic is configured to assert the switch control signal preceding a positive to negative edge transition of the transformer signal by a minimum interval, wherein the minimum interval is determined in accordance with a minimum peak inductor current threshold.

10. The switch controller of claim 9 , wherein the controller logic is configured to assert the switch control signal preceding a positive to negative edge transition by a maximum period, wherein the maximum period is determined in accordance with a maximum inductor current threshold.

11. The switch controller of claim 8 , wherein the controller logic is configured to de-assert the switch control signal following a positive to negative edge transition of the transformer signal.

12. The switch controller of claim 11 , wherein the controller logic is configured to de-assert the switch control signal following the positive to negative edge transition in accordance with a triggering value of the sense signal.

13. The switch controller of claim 12 , wherein the triggering value of the sense signal is indicative of zero inductor current.

14. The switch controller of claim 12 , wherein the triggering value of the sense signal corresponds to a positive value of the inductor current and the triggering value is transferred to a load circuit.

15. The switch controller of claim 7 , wherein the controller logic is configured to assert and de-assert the switch control signal multiple times per half-period of the transformer signal.

16. The switch controller of claim 15 , wherein the controller logic includes a multi-pulse enable input configured to prevent multiple assertions of the switch control signal in a single half-period of the transformer signal until detecting the sense signal above a specified threshold.

17. The switch controller of claim 15 , wherein the controller logic is configured to first assert the switch control signal preceding a positive to negative edge transition by a multi-pulse interval, wherein the multi-pulse interval includes a charging interval and a dissipation interval, wherein the charging interval is sufficient to charge the inductor in accordance with a minimum peak inductor current threshold and wherein the dissipation interval is sufficient to encompass a plurality of dissipation cycles.

18. The switch controller of claim 17 , wherein each of the dissipation cycles includes a de-assertion of the switch control signal for a first duration and an assertion of the switch control signal for a second duration.

19. The switch controller of claim 17 , wherein the controller logic is configured to determine a duration of the multi-pulse interval in accordance with the load signal.

20. The switch controller of claim 7 , wherein the controller logic is configured to:

initialize to an on state with the switch control signal asserted; and

monitor an oscillation signal indicating the transformer oscillating and an edge signal indicating an edge transition of the transformer signal.

21. The switch controller of claim 20 , wherein the controller logic is configured to:

respond, to detecting the oscillation signal and the edge signal both asserted while in the on state by:

de-asserting the switch control signal;

transitioning to an edge state; and

monitoring a compare low signal indicative of the sense signal below a low threshold.

22. The switch controller of claim 21 , wherein the controller logic is configured to:

respond to detecting the compare low signal asserted while in the edge state by:

clearing an off counter;

transitioning to an off state; and

monitoring an off timeout signal indicative of the off counter exceeding a maximum threshold.

23. The switch controller of claim 22 , wherein the controller logic is configured to:

respond to detecting the off timeout signal while in the off state by:

asserting the switch control signal; and

transitioning to the on state.

24. The switch controller of claim 22 , wherein the controller logic is configured to:

respond, while in the off state, to detecting the oscillation signal and a compare high signal both asserted, by:

de-asserting the switch control signal;

clearing a continuous current mode off counter;

transitioning to a continuous current mode off state; and

monitoring the continuous current mode off counter indicative of a duration of the continuous current mode off state.

25. The switch controller of claim 24 , wherein the controller logic is configured to:

respond, while in the continuous current mode off state, to detecting the continuous current mode off counter exceeding a continuous current mode off threshold by:

asserting the switch control signal;

clearing a continuous current mode on counter; and

transitioning to a continuous current mode on state.

26. The switch controller of claim 25 , wherein the controller logic is configured to:

respond, while in the continuous current mode on state to detecting the compare high signal by:

de-asserting the switch control signal;

clearing the continuous current mode off counter; and

transitioning to the continuous current mode off state; and

respond, while in the continuous current mode on state, to detecting the continuous current mode on counter exceeding a continuous current mode on threshold and the compare low signal not asserted by:

de-asserting the switch control signal;

clearing the off counter; and

transitioning to the off state.

27. The switch controller of claim 7 , wherein the controller logic includes:

a first comparator configured to generate the compare high signal in accordance with the sense signal and a high reference voltage signal; and

a second comparator configured to generate the compare low signal in accordance with the sense signal and a low reference voltage signal.

28. The switch controller of claim 27 , wherein the controller logic includes:

an oscillation detector configured to generate the oscillation signal in accordance with the compare low signal, wherein the oscillation signal initializes to a true value and remains true unless the compare low signal is deasserted for a duration exceeding a predetermined interval.

29. A low voltage apparatus suitable for use with an electronic transformer configured to generate a transformer output signal including a transformer output current and a transformer output voltage, the low voltage apparatus comprising:

a boost converter stage comprising:

an inductor configured to receive the transformer output current as an inductor current;

a rectifier configured to generate a rectified current by rectifying the inductor current;

a switch configured to influence a current path of the rectified current in accordance with a switch control signal; and

a controller, comprising:

at least one controller input, including:

a transformer input configured to receive the transformer output voltage; and

controller logic configured to synchronize transitions of the switch control signal with transformer output transitions indicated by the transformer input.

30. The apparatus of claim 29 , wherein the boost converter stage further includes:

a capacitor connected across an output of the boost converter stage;

a diode including an anode connected to the switch node and a cathode connected to a first terminal of the boost converter stage output; and

wherein the switch includes a first output terminal connected to the switch node and wherein the switch is configured to draw a switch current from the switch node, wherein the switch current is approximately equal to:

the rectified current when the switch control signal is asserted; and

zero when the switch control signal is not asserted.

31. The apparatus of claim 30 , wherein the controller logic is configured to synchronize the switch control signal with the transformer output transitions wherein a peak inductor current is greater than a minimum peak inductor current threshold and less than a maximum inductor current limit.

32. A switch control method, comprising:

receiving a set of one or more controller inputs, wherein the controller inputs include a transformer output of an electronic transformer; and

generating a switch control signal based, at least in part, on the controller inputs, wherein the switch control signal is configured to control a conductive state of a switch configured to influence a current path of a rectified current generated by a rectifier configured to rectify an inductor current of an inductor coupled to the transformer output; and

synchronizing assertions of the switch control signal with transitions of the transformer output.

33. The method of claim 32 , wherein generating the switch control signal includes:

initializing to an off state with the switch control signal asserted;

monitoring an oscillation signal indicating the transformer oscillating, an edge signal indicating an edge transition of the transformer output, a compare high signal indicating an inductor current in compliance with a maximum inductor current threshold, and a compare low signal indicating an inductor current in compliance with a minimum peak inductor current threshold; and

responding, while in the off state, to detecting the oscillation signal and the compare high signal both asserted, by:

de-asserting the switch control signal;

clearing a continuous current mode off counter indicative of a duration of a continuous current mode off state; and

transitioning to the continuous current mode off state.

34. The method of claim 33 , further comprising:

responding, while in the continuous current mode off state, to detecting the continuous current mode off counter exceeding a continuous current mode off threshold by:

asserting the switch control signal;

clearing a continuous current mode on counter indicative of a duration of a continuous current mode on state; and

transitioning to the continuous current mode on state.

35. The apparatus of claim 34 , further comprising:

responding, while in the continuous current mode on state to detecting the compare high signal by:

de-asserting the switch control signal;

clearing the continuous current mode off counter; and

transitioning to the continuous current mode off state; and

responding, while in the continuous current mode on state, to detecting:

the continuous current mode on counter exceeding a continuous current mode off threshold; and

the compare low signal not asserted;

by transitioning to the off state.