Electronic Circuits and Techniques for Maintaining a Consistent Power Delivered to a Load

• US 20130009556A1
• Filed: 07/06/2011
• Published: 01/10/2013
• Est. Priority Date: 07/06/2011
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Szczeszynski, Gregory, Mangtani, Vijay
• Granted Patent: US 9,265,104 B2
• Time in Patent Office: Days
• US Class Current: 315/185.R
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

Circuits and methods used therein provide an adjustable average current through a load in accordance with a pulse width modulated (PWM) signal. A condition detection circuit is configured to identify a condition of the electronic circuit and to generate a condition signal indicative of the condition. A current extension circuit is coupled receive the condition signal and coupled to receive the PWM signal. The current extension circuit is configured to generate, at the output node of the current extension circuit, an extended PWM signal having a first state and a second state. The first state of the extended PWM signal longer in time than a first state of the PWM signal by an amount related to a value or a state of the condition signal. Current pulses through the load are extended to be longer in accordance with the extended PWM signal.

Claims

1. An electronic circuit to provide an adjustable average current through a load, the electronic circuit comprising:

a PWM input node coupled to receive a pulse width modulated (PWM) signal having first and second states with respective adjustable time durations;

a condition detection circuit configured to identify a condition of the electronic circuit and to generate a condition signal indicative of the condition; and

a current extension circuit comprising an input node, a control node, and an output node, the input node of the current extension circuit coupled receive the condition signal, the control node of the current extension circuit coupled to the PWM input node, wherein the current extension circuit is configured to generate, at the output node of the current extension circuit, an extended PWM signal having a first state and a second state, the first state of the extended PWM signal longer in time than the first state of the PWM signal by an amount related to a value or a state of the condition signal.

2. The electronic circuit of claim 1, wherein the longer time of the first state of the extended PWM signal is longer by a determined time amount determined in relation to a value of the condition signal.

3. The electronic circuit of claim 1, wherein the longer time of the first state of the extended PWM signal is longer by a predetermined time when the condition signal has a first state and not longer by the predetermined time when the condition signal has a second different state.

4. The electronic circuit of claim 1, further comprising:

a load connection node configured to couple to the load; and

a current regulator circuit comprising an input node, an output node, and a current enable node, a selected one of the input node or the output node of the current regulator circuit coupled to the load connection node, the current enable node coupled to receive the extended PWM signal, the current regulator circuit configured to pass a predetermined current from the input node to the output node, wherein the predetermined current is passed or not passed depending upon the first or the second state, respectively, of the extended PWM signal.

5. The electronic circuit of claim 1, wherein the load comprises a series coupled string of light emitting diodes.

6. The electronic circuit of claim 1, wherein the condition detection circuit comprises at least one of:

an average current detection circuit configured to generate the condition signal having a value related to the average current through the load;

a dv/dt detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a rate of change of a power supply voltage being above a rate of change threshold;

a voltage level detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a value of the power supply voltage being below a power supply voltage threshold;

a static circuit configured to generate the condition signal as a static signal having a static value;

a short duty cycle detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a duty cycle of the PWM signal being below a duty cycle threshold;

or

a soft start short duty cycle detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a duty cycle of the PWM signal being below the duty cycle threshold in combination with a state of a soft start signal, wherein the soft start signal comprises a two state signal having a state delayed from a startup of the electronic circuit.

7. The electronic circuit of claim 6, further comprising:

a load connection node configured to couple to the load; and

a current regulator circuit comprising an input node, an output node, and a current enable node, a selected one of the input node or the output node of the current regulator circuit coupled to the load connection node, the current enable node coupled to receive the extended PWM signal, the current regulator circuit configured to pass a predetermined current from the input node to the output node, wherein the predetermined current is passed or not passed depending upon the first or the second state, respectively, of the extended PWM signal.

8. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

an average current detection circuit configured to generate the condition signal having a value related to the average current through the load.

9. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

a dv/dt detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a rate of change of a power supply voltage being above a rate of change threshold.

10. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

a voltage level detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a value of a power supply voltage being below a power supply voltage threshold.

11. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

a static circuit configured to generate the condition signal as a static signal having a static value.

12. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

a short duty cycle detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a duty cycle of the PWM signal being below a duty cycle threshold.

13. The electronic circuit of claim 1, wherein the condition detection circuit comprises:

a soft start short duty cycle detection circuit configured to generate the condition signal as a two state signal having the first state resulting from a duty cycle of the PWM signal being below a duty cycle threshold in combination with a state of a soft start signal, wherein the soft start signal comprises a two state signal having a state delayed from a startup of the electronic circuit.

14. The electronic circuit of claim 1, wherein the current extension circuit comprises:

a reference integrator coupled to receive a reference voltage and configured to generate a first integrated signal;

an average current sense integrator coupled to receive a signal having a value related to a value of the adjustable average current through the load and configured to generate a second integrated signal; and

a comparator coupled to receive the first and second integrated signals and configured to generate the extended PWM signal in accordance with a comparison of the first and second integrated signals.

15. The electronic circuit of claim 1, wherein the current extension circuit comprises:

a pulse extender circuit coupled to receive the PWM signal and configured to generate the extended PWM signal; and

a switch circuit coupled to receive the PWM signal, coupled to receive the extended PWM signal, coupled to receive the condition signal, and configured to generate an output signal, wherein the output signal from the switch circuit is a selected one of the PWM signal or the extended PWM signal, selected in accordance with a state of the condition signal.

16. The electronic circuit of claim 1, further comprising:

a switching regulator control node; and

a switching regulator controller having an input node, an output node, and an enable node, the output node of the switching regulator controller coupled to the switching regulator control node, the input node of the switching regulator controller coupled to receive a feedback voltage related to the average current through the load, and the enable node of the switching regulator controller coupled to receive the extended PWM signal, wherein the switching regulator controller does or does not generate a switching signal at the output node of the switching regulator controller depending upon the first or the second state, respectively, of the extended PWM signal.

17. The electronic circuit of claim 16, wherein the switching regulator control node is configured to couple to a switching regulator.

18. A method of generating an adjustable average current through a load with an electronic circuit, the method comprising:

receiving a pulse width modulated (PWM) signal having first and second states with respective adjustable time durations;

detecting a condition of the electronic circuit;

generating a condition signal related to the condition;

generating an extended PWM signal having first and second states with respective time durations in accordance with the condition signal, wherein the first state of the extended PWM signal is longer than the first state of the PWM; and

coupling a current regulator to the load, the current regulator coupled to receive the extended PWM signal, the current regulator circuit configured to pass a predetermined current from the input node to the output node, wherein the predetermined current is passed or not passed depending upon the first or the second state, respectively, of the extended PWM signal.

19. The method of claim 18, wherein the load comprises a series coupled string of light emitting diodes.

20. The method of claim 18, wherein the detecting the condition comprises:

detecting a value of the average current through the load, wherein the condition signal has a value related to the value of the average current.

21. The method of claim 18, wherein the detecting the condition comprises:

detecting a rate of change of a power supply voltage being above a rate of change threshold, wherein the condition signal comprises a two state signal having the first state resulting from the rate of change of the power supply voltage being above the rate of change threshold.

22. The method of claim 18, wherein the detecting the condition comprises:

detecting a value of a power supply voltage being below a power supply voltage threshold, wherein the condition signal comprises a two state signal having the first state resulting from the power supply voltage being below the power supply voltage threshold.

23. The method of claim 18, wherein the detecting the condition comprises:

detecting a duty cycle of the PWM signal being below a duty cycle threshold, wherein the condition signal comprises a two state signal having the first state resulting from the PWM signal being below the duty cycle threshold.

24. The method of claim 18, wherein the detecting the condition comprises:

detecting a duty cycle of the PWM signal being below a duty cycle threshold; and

detecting a state of a soft start signal, wherein the soft start signal comprises a two state signal having a state delayed from a startup of the electronic circuit, and wherein the condition signal comprises a two state signal having the first state resulting from the PWM signal being below the duty cycle threshold and in combination with the detected state of the soft start signal.

25. The method of claim 18, wherein the generating the extended PWM signal comprises:

integrating a reference voltage to generate a first integrated signal;

integrating a signal having a value related to a value of the adjustable average current through the load to generate a second integrated signal; and

comparing the first and second integrated signals.

26. The method of claim 18, wherein the generating the extended PWM signal comprises:

receiving the PWM signal;

receiving the extended PWM signal;

receiving the condition signal; and

generating an output signal as a selected one of the PWM signal or the extended PWM signal, selected in accordance with a state of the condition signal.

27. The method of claim 18, further comprising:

controlling a switching regulator in accordance with the extended PWM signal.