Switch-mode drive sensing of reverse recovery in bipolar junction transistor (BJT)-based power converters

• US 9,609,701 B2
• Filed: 02/27/2015
• Issued: 03/28/2017
• Est. Priority Date: 02/27/2015
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Rengachari, Thirumalai, Melanson, John L., Zanbaghi, Ramin, Drakshapalli, Prashanth, Singh, Rahul, Dutta, Arnab Kumar
• Primary Examiner(s): Le, Tung X
• Application Number:
  US14/634,716
• Publication Number:
  US 20160255685A1
• Time in Patent Office: 760 Days
• Field of Search: 315/209.R, 315224-225, 315/291, 315/294, 315/297, 315/307, 363/21
• US Class Current: 1/1
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• 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: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

A bipolar junction transistor (BJT) may be used in a power stage DC-to-DC converter, such as a converter in LED-based light bulbs. The power stage may be operated by a controller to maintain a desired current output to the LED load. The controller may operate the power stage by monitoring a start and end of a reverse recovery time of the BJT. Information regarding the start and end of the reverse recovery time may be used in the control of the power stage to improve efficiency of the power stage.

Claims

1. A method, comprising:

driving a base current from a base current source to a base of a bipolar junction transistor (BJT) to maintain conduction of the bipolar junction transistor (BJT) during a first time period;

disconnecting the base current source from the bipolar junction transistor (BJT) for a second time period, wherein the second time period comprises a reverse recovery time period during which the bipolar junction transistor (BJT) remains conducting while the base current source is disconnected; and

detecting an end of the reverse recovery time period by monitoring a voltage at the base of the bipolar junction transistor (BJT).

2. The method of claim 1, wherein the step of detecting the end of the reverse recovery time period comprises detecting the base voltage is at least 2 Volts below a supply voltage.

3. The method of claim 1, wherein the step of driving the base current maintains conduction of the bipolar junction transistor (BJT) to charge an energy storage device coupled to a load.

4. The method of claim 3, further comprising:

detecting de-engergization of the energy storage device during the second time period; and

repeating the step of driving the base current after detecting the de-energization.

5. The method of claim 4, wherein the step of detecting de-energization of the energy storage device comprises detecting a zero current through the energy storage device.

6. The method of claim 5, wherein the step of detecting the zero current comprises detecting the zero current at the base of the bipolar junction transistor (BJT).

7. The method of claim 4, wherein the step of detecting de-energization comprises coupling a resistor to the base of the bipolar junction transistor (BJT) to form a high pass filter (HPF) with a capacitor, wherein the capacitor is coupled to the base of the bipolar junction transistor (BJT) and an emitter of the bipolar junction transistor (BJT).

8. The method of claim 7, wherein the high pass filter (HPF) comprises at least one pole at a frequency greater than an expected oscillation frequency of a voltage at a collector of the bipolar junction transistor (BJT) when the energy storage device is de-energized.

9. The method of claim 4, wherein the step of detecting de-energization comprises detecting a ringing voltage at a collector of the bipolar junction transistor (BJT).

10. The method of claim 9, wherein the step of repeating the step of driving the base current comprises coupling the base current source to the base of the bipolar junction transistor (BJT) prior to approximately a minimum voltage at the collector of the bipolar junction transistor (BJT) during the detected ringing.

11. The method of claim 10, wherein the step of coupling the base current source prior to approximately a minimum voltage comprises coupling the base current source a fixed delay offset duration prior to approximately the minimum voltage.

12. The method of claim 10, further comprising:

measuring a turn-on delay of the bipolar junction transistor when repeating the step of driving the base current; and

again repeating the step of driving the base current by coupling the base current source to the base of the bipolar junction transistor (BJT) a time prior to approximately a minimum voltage at the collector of the bipolar junction transistor (BJT), wherein the time prior is based, at least in part, on the measured turn-on delay.

13. An apparatus, comprising:

a controller configured to couple to a base of a bipolar junction transistor (BJT);

wherein the controller is configured to perform the steps comprising;

driving a base current from a base current source to the base of the bipolar junction transistor (BJT) to maintain conduction of the bipolar junction transistor (BJT) during a first time period;

disconnecting the base current source from the bipolar junction transistor (BJT) for a second time period, wherein the second time period comprises a reverse recovery time period during which the bipolar junction transistor (BJT) remains conducting while the base current source is disconnected; and

detecting an end of the reverse recovery time period by monitoring a voltage at the base of the bipolar junction transistor (BJT).

14. The apparatus of claim 13, wherein the step of detecting the end of the reverse recovery time period comprises detecting the base voltage is at least 2 Volts below a supply voltage.

15. The apparatus of claim 13, wherein the step of driving the base current maintains conduction of the bipolar junction transistor (BJT) to charge an energy storage device coupled to a load.

16. The apparatus of claim 15, wherein the controller is further configured to perform the steps of:

detecting de-engergization of the energy storage device during the second time period; and

repeating the step of driving the base current after detecting the de-energization.

17. The apparatus of claim 16, wherein the step of detecting de-energization of the energy storage device comprises detecting a zero current through the energy storage device.

18. The apparatus of claim 17, wherein the step of detecting the zero current comprises detecting the zero current at the base of the bipolar junction transistor (BJT).

19. The apparatus of claim 16, wherein the step of detecting de-energization comprises coupling a resistor to the base of the bipolar junction transistor (BJT) to form a high pass filter (HPF) with a capacitor, wherein the capacitor is coupled to the base of the bipolar junction transistor (BJT) and an emitter of the bipolar junction transistor (BJT).

20. The apparatus of claim 19, wherein the high pass filter (HPF) comprises at least one pole at a frequency greater than an expected oscillation frequency of a voltage at a collector of the bipolar junction transistor (BJT) when the energy storage device is de-energized.

21. The apparatus of claim 16, wherein the step of detecting de-energization comprises detecting a ringing voltage at a collector of the bipolar junction transistor (BJT).

22. The apparatus of claim 21, wherein the step of repeating the step of driving the base current comprises coupling the base current source to the base of the bipolar junction transistor (BJT) prior to approximately a minimum voltage at the collector of the bipolar junction transistor (BJT) during the detected ringing.

23. The apparatus of claim 22, wherein the step of coupling the base current source prior to approximately a minimum voltage comprises coupling the base current source a fixed delay offset duration prior to approximately the minimum voltage.

24. The apparatus of claim 22, wherein the controller is further configured to perform the steps of:

measuring a turn-on delay of the bipolar junction transistor when repeating the step of driving the base current; and

again repeating the step of driving the base current by coupling the base current source to the base of the bipolar junction transistor (BJT) a time prior to approximately a minimum voltage at the collector of the bipolar junction transistor (BJT), wherein the time prior is based, at least in part, on the measured turn-on delay.