Single pin control of bipolar junction transistor (BJT)-based power stage

• US 9,253,833 B2
• Filed: 05/16/2014
• Issued: 02/02/2016
• Est. Priority Date: 05/17/2013
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Zanbaghi, Ramin, Melanson, John L., Choi, Jieyeon
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Kaiser, Syed M
• Application Number:
  US14/280,474
• Publication Number:
  US 20140339995A1
• Time in Patent Office: 627 Days
• Field of Search: 315/224, 315/291, 315/294, 315/191, 315/307
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A power stage for light emitting diode (LED)-based light bulbs may include a bipolar junction transistor (BJT). The base of BJT switch may be biased externally and the operation of the BJT may be through a single pin to the emitter of the BJT. A controller integrated circuit (IC) may control the power stage through the main BJT'"'"'s emitter pin in an emitter-controlled BJT-based power stage. The emitter-controlled BJT-based power stage may replace the conventional buck-boost power stage topology. For example, the controller may activate and deactivate a switch coupling the BJT'"'"'s emitter to ground. A power supply for the controller IC may be charged from a reverse recovery of charge from the BJT, and the reverse recovery controlled by the controller IC.

Claims

1. An apparatus, comprising:

an integrated circuit (IC) configured to couple to a bipolar junction transistor (BJT) through a single pin that is configured to couple to an emitter of the bipolar junction transistor (BJT), wherein the integrated circuit (IC) comprises;

a switch configured to couple to the emitter of the bipolar junction transistor (BJT);

a current detector coupled to the switch and configured to detect when a current from the emitter of the bipolar junction transistor (BJT) reaches a threshold value; and

a controller coupled to the switch and to the current detector and configured to;

control delivery of power to a load by operating the switch;

sense a current through the bipolar junction transistor (BJT); and

turn off the switch when the current detector detects the threshold value is reached.

2. The apparatus of claim 1, further comprising the bipolar junction transistor (BJT) comprising a base, the emitter, and a collector, wherein the emitter is coupled to the integrated circuit (IC).

3. The apparatus of claim 2, further comprising a base drive circuit coupled to the base of the bipolar junction transistor (BJT), wherein the base drive circuit is configured to bias the base of the bipolar junction transistor (BJT) from a power supply node.

4. The apparatus of claim 3, wherein the power supply node is coupled to an external source.

5. The apparatus of claim 1, wherein the controller is configured to:

turn on the switch to direct current to charge an inductor during a first time period, during which a base charge is accumulated at the base of the bipolar junction transistor (BJT); and

turn off the switch to begin a reverse recovery of the base charge at the base of the bipolar junction transistor (BJT).

6. The apparatus of claim 5, wherein turning off the switch causes the bipolar junction transistor (BJT) to discharge a base charge from the base of the bipolar junction transistor (BJT) until the bipolar junction transistor (BJT) turns off, after which current from the inductor is directed to a lighting load.

7. The apparatus of claim 5, wherein the reverse recovery of the charge is used to charge a chip supply for the integrated circuit (IC) by redirecting current from the emitter of the BJT through the IC by redirecting current from the emitter of the BJT through the IC.

8. The apparatus of claim 1, wherein the current detector comprises:

a sense resistor configured to be coupled to the emitter of the bipolar junction transistor (BJT); and

a comparator coupled to the sense resistor and wherein the comparator is configured to couple to a threshold voltage corresponding to the threshold value, wherein the comparator is further configured to output a comparator signal based, at least in part, on a comparison of a voltage at the emitter of the bipolar junction transistor (BJT) and the threshold voltage, and

wherein the controller is configured to turn off the switch based, at least in part, on the comparator signal.

9. The apparatus of claim 1, further comprising a reverse-recovery control circuit configured to be coupled to the emitter of the bipolar junction transistor (BJT) and configured to be coupled to a power supply node, wherein the reverse-recovery control circuit is configured to regulate a discharge current from the base of the bipolar junction transistor (BJT) to the power supply node.

10. The apparatus of claim 9, wherein the reverse-recovery control circuit comprises:

a plurality of diodes; and

a plurality of switches corresponding to the plurality of diodes, each of the plurality of switches being coupled in parallel with one of the plurality of diodes.

11. The apparatus of claim 1, further comprising:

a capacitive coupling that is configured to be coupled between the emitter and a collector of the bipolar junction transistor (BJT); and

a zero current detection block configured to be coupled to the emitter of the bipolar junction transistor (BJT) and configured to detect a ringing at the collector of the bipolar junction transistor (BJT) through the high-pass filter,

wherein the controller is coupled to the current detection block and configured to turn on the switch after the ringing is detected.

12. The apparatus of claim 11, wherein the controller is configured to:

detect a valley of the ringing; and

turn on the switch approximately at the valley of the ringing.

13. The apparatus of claim 11, wherein the capacitive coupling comprises a high-pass filter (HPF) comprising:

a capacitor configured to be coupled to the emitter and the collector of the bipolar junction transistor (BJT); and

a resistor configured to be coupled to the emitter of the bipolar junction transistor (BJT).

14. A method, comprising:

configuring an integrated circuit (IC) to control a bipolar junction transistor (BJT) through a single pin that is configured to couple the integrated circuit (IC) to the bipolar junction transistor (BJT);

controlling, by the integrated circuit (IC), delivery of power to a load by operating a switch configured to couple to an emitter of the bipolar junction transistor (BJT) through the single pin, wherein the step of operating the switch further comprises;

turning on the switch to direct current to the load during a first time period, during which a base charge is accumulated at the base of the bipolar junction transistor (BJT); and

turning off the switch to begin a reverse recovery of the base charge at the base of the bipolar junction transistor (BJT);

sensing, by the integrated circuit (IC), current through the bipolar junction transistor (BJT) through the single pin;

detecting when an emitter current from the emitter of the bipolar junction transistor (BJT) reaches a threshold value by comparing a voltage at a sense resistor coupled to the emitter of the bipolar junction transistor (BJT) with a reference voltage; and

turning off the switch after detecting the emitter current reaches the threshold value.

15. The method of claim 14, further comprising coupling the integrated circuit (IC) to the bipolar junction transistor (BJT).

16. The method of claim 15, further comprising biasing a base of the bipolar junction transistor (BJT) with an approximately fixed voltage from a power supply node.

17. The method of claim 16, wherein the step of operating the switch further comprises:

turning on the switch to direct current to the load during a first time period, during which a base charge is accumulated at the base of the bipolar junction transistor (BJT); and

turning off the switch to begin a reverse recovery of the base charge at the base of the bipolar junction transistor (BJT).

18. The method of claim 17, wherein turning off the switch causes the bipolar junction transistor (BJT) to discharge a base charge from the base of the bipolar junction transistor (BJT) until the bipolar junction transistor (BJT) turns off, after which current from the inductor is directed to a lighting load.

19. The method of claim 17, further comprising recovering current from the base charge at the base of the bipolar junction transistor (BJT) to supply a controller.

20. The method of claim 17, further comprising regulating a discharge of the base charge from the base of the bipolar junction transistor (BJT).

21. The method of claim 20, wherein the step of regulating further comprises shorting out one or more diodes.

22. An apparatus, comprising:

a lighting load comprising a plurality of light emitting diodes (LEDs);

a bipolar junction transistor (BJT) comprising a base, an emitter, and a collector, wherein the collector of the bipolar junction transistor (BJT) is coupled to an input node; and

an integrated circuit (IC) configured to couple to the bipolar junction transistor (BJT) through a single pin that is configured to couple to the emitter of the bipolar junction transistor (BJT), wherein the integrated circuit (IC) comprises;

a switch configured to couple to the emitter of the bipolar junction transistor (BJT);

a current sensor coupled to the switch and configured to detect when a current from the emitter of the bipolar junction transistor (BJT) reaches a threshold value; and

a controller coupled to the switch and configured to control delivery of power to the lighting load by operating the switch and configured to sense a current through the bipolar junction transistor (BJT), wherein the controller is configured to operate the switch based on the current sensor detecting the current reaching the threshold value.

23. The apparatus of claim 22, further comprising:

a rectifier coupled to the input node;

a dimmer coupled to the rectifier; and

a line voltage input node coupled to the dimmer.

24. The apparatus of claim 22, wherein the controller and the switch are integrated into an integrated circuit (IC), and wherein the integrated circuit (IC) controls operation of the bipolar junction transistor (BJT) through the single pin.

25. The apparatus of claim 22, further comprising a reverse recovery control circuit configured to be coupled to the base of the bipolar junction transistor (BJT), wherein the controller is configured to operate the reverse recovery control circuit to regulate a discharge of base current from the base of the bipolar junction transistor (BJT).

26. The apparatus of claim 22, further comprising a zero current detect (ZCD) circuit configured to be coupled to the emitter of the bipolar junction transistor (BJT),

wherein the zero current detect (ZCD) circuit is further configured to detect a discharge of an inductor coupled to the collector of the bipolar junction transistor (BJT).

27. The apparatus of claim 26, wherein the controller is configured to operate the switch based, at least in part, on the detection of the discharge of the inductor by the zero current detect (ZCD) circuit.