Circuits and methods for determining peak current

• US 9,042,124 B1
• Filed: 04/04/2012
• Issued: 05/26/2015
• Est. Priority Date: 04/06/2011
• Status: Expired due to Fees

• Current Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Choi, Jinho, Peng, Hao, Zhang, Wanfeng, Doan, Tuyen
• Primary Examiner(s): Laxton, Gary L
• Assistant Examiner(s): DEMISSE, AFEWORK S
• Application Number:
  US13/439,097
• Time in Patent Office: 1,147 Days
• Field of Search: 363 2101- 2118, 363/97, 363/15, 363/16, 363/131, 363/20
• US Class Current: 363/20
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

Embodiments include circuits and methods to determine peak current for current regulation. A control signal circuit monitors a current on the primary side of a transformer based a turn on time of a switch coupled to the primary side. The control signal circuit determines whether the monitored current exceeds an over-current protection threshold, and determines a duration that the monitored current exceeds the over-current protection threshold. The control signal circuit determines a peak primary current in the primary side based on the over-current protection threshold, the duration that the monitored current exceeds the over-current protection threshold, and the turn on time of the switch. The control signal circuit controls the turn on time for the switch based on the determined peak primary current.

Claims

1. A method comprising:

monitoring a current on a primary side of a transformer based on an on time of a switch coupled to the primary side;

determining a first threshold, a duration that the monitored current exceeds the first threshold, and the on time of the switch; and

determining a peak primary current in the primary side by multiplying a second threshold, the second threshold being an over-current protection threshold corresponding to the first threshold, and a first ratio, the first ratio being the on time of the switch divided by the on time of the switch minus said duration.

2. The method of claim 1, wherein the first threshold is a voltage corresponding to a value of the current on the primary side of the transformer.

3. The method of claim 1, wherein said duration comprises a time delay from a low pass filter.

4. The method of claim 1, further comprising outputting a signal generated based on the determined peak primary current to control the on time of the switch in a control loop.

5. The method of claim 4, further comprising generating an average current based on the peak primary current.

6. The method of claim 5, further comprising comparing the average current with a reference current to determine an error signal.

7. The method of claim 6, further comprising altering the on time of the switch based on the error signal.

8. A circuit comprising:

a transformer having a primary side and a secondary side, the primary side coupled to receive an input voltage;

a load coupled to the secondary side;

a switch coupled to the primary side; and

a control signal circuit coupled to the switch, the control signal circuit configured to;

monitor a current on the primary side of the transformer based on an on time of the switch;

determining a first threshold, a duration that the monitored current exceeds the first threshold, and the on time of the switch; and

determining a peak primary current in the primary side by multiplying a second threshold, the second threshold being an over-current protection threshold corresponding to the first threshold, and a first ratio, the first ratio being the on time of the switch divided by the on time of the switch minus said duration.

9. The circuit of claim 8, wherein the first threshold is a voltage corresponding to a value of the current on the primary side of the transformer.

10. The circuit of claim 8, further comprising a low pass filter, wherein said duration comprises a time delay from a low pass filter.

11. A circuit comprising:

a sense circuit to sense a first current in a primary stage of a transformer, the sense circuit being coupled to a terminal of a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) to sense the first current when the MOSFET is on;

a first comparator having a first input to receive a first signal corresponding to the first current and a second input to receive a second signal corresponding to a second, maximum current, the first comparator generating a pulse when the first current exceeds the second, maximum current; and

a driver to receive a first signal and generate a second signal for turning the MOSFET on and off, a third, peak primary current being determined by multiplying the second, maximum current and a first ratio, wherein the first ratio is a period of time the MOSFET is turned on divided by the period of time the MOSFET is turned on minus a first time period.

12. The circuit of claim 11, further comprising:

an estimator circuit to receive the pulse from the first comparator and determine the third, peak primary current and a fourth, average secondary current;

an accumulator to determine a difference between the fourth, average secondary current and a fifth, reference current to produce an error signal; and

a controller to receive the error signal and produce the first signal, wherein the first signal is turned off when the pulse is generated.

13. The circuit of claim 11, wherein the sense circuit is coupled to a resistor.

14. The circuit of claim 11, wherein the sense circuit comprises an amplifier.

15. The circuit of claim 11, wherein the sense circuit comprises a low pass filter.

16. The circuit of claim 15, wherein the first time period is a length of time of the pulse plus a time delay of the low pass filter.

17. The circuit of claim 11, further comprising one or more second comparators, each second comparator having a first input to receive the first signal corresponding to the first current and a second input to receive different signals corresponding to different second, maximum currents, wherein an output of said first comparator or said one or more second comparators is selected to set a fourth, secondary current in the transformer.