EFFICIENCY MEASURING CIRCUIT FOR DC-DC CONVERTER WHICH CALCULATES INTERNAL RESISTANCE OF SWITCHING INDUCTOR BASED ON DUTY CYCLE

• US 20110156687A1
• Filed: 04/06/2010
• Published: 06/30/2011
• Est. Priority Date: 12/24/2009
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Chiacchia, Robert C., Witte, Hellmuth Stephen, Manlove, Gregory Jon, Gardner, Andrew Joseph
• Granted Patent: US 8,278,895 B2
• Time in Patent Office: Days
• US Class Current: 323/284
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

An efficiency measuring circuit may measure the efficiency of a DC-DC converter having a switching inductor with an internal DC resistance and a plurality of electronic switches that control current through the inductor. A duty cycle circuit may measure the duty cycle of current flowing through one of the electronic switches. A current sense circuit may measure the current flowing through one of the electronic switches. An inductor voltage sensor circuit may measure the voltage across the inductor. A computation circuit may compute the internal DC resistance of the switching inductor based in part on the duty cycle measured by the duty cycle circuit and the current measured by the current sense circuit. The computation circuit may also compute the efficiency of the DC-DC converter.

Claims

1. A circuit for connecting to a DC-DC converter having a switching inductor with an internal DC resistance and a plurality of electronic switches that control current through the inductor, the circuit comprising:

a duty cycle circuit configured to measure the duty cycle of current flowing through one of the electronic switches;

a current sensor circuit configured to measure the current flowing through one of the switches;

a voltage sensor circuit configured to measure the voltage across the inductor or across another element which has resistance and is in series with the inductor; and

a computation circuit configured to compute the;

internal DC resistance of the switching inductor or other element based in part on the duty cycle measured by the duty cycle circuit; and

the current measured by the current sense circuit; and

the voltage across the inductor or other element.

2. The circuit of claim 1 wherein the DC-DC converter is a step down DC-DC converter which includes a top switch configured to controllably connect the inductor to a supply voltage and a bottom switch configured to controllably connect the inductor to a ground reference, and wherein the duty cycle circuit is configured to measure the duty cycle of current flowing through the top switch and the current sensor circuit is configured to measure the current flowing through the top switch.

3. The circuit of claim 2 wherein the top switch includes a control input and the duty cycle circuit is configured to measure the duty cycle of current flowing through the top switch by measuring the duty cycle of a signal delivered to the control input of the top switch.

4. The circuit of claim 3 wherein the duty cycle circuit includes:

a threshold circuit configured to generate a threshold voltage; and

a comparator configured to compare a signal representative of the signal delivered to the control input of the top switch with the threshold voltage.

5. The circuit of claim 4 wherein the duty cycle circuit includes a voltage limiter configured to limit the magnitude of the signal representative of the signal delivered to the control input of the top switch.

6. The circuit of claim 4 wherein the comparator has an output and wherein the duty cycle circuit includes a filter configured to filter the output of the comparator.

7. The circuit of claim 2 wherein the duty cycle circuit is configured to measure the duty cycle of current flowing through the top switch by measuring the duty cycle of a signal representative of the voltage drop across a sense resistor in series with the top switch.

8. The circuit of claim 7 wherein the duty cycle circuit includes:

a voltage offset circuit configured to generate an offset voltage; and

a comparator configured to compare the signal representative of the voltage drop across the sense resistor with the offset voltage.

9. The circuit of claim 8 wherein the comparator has an output and wherein the duty cycle circuit includes a filter configured to filter the output of the comparator.

10. The circuit of claim 1 wherein the computation circuit is configured to cause the computed internal DC resistance of the switching inductor or other element to be stored in an electronic memory device.

11. The circuit of claim 10 wherein the computation circuit is configured to compute the efficiency of the DC-DC converter based in part on the stored value of the internal DC resistance of the switching inductor or other element.

12. The circuit of claim 11 wherein the computation circuit is configured to compute the internal DC resistance of the switching inductor or other element based on the duty cycle of current flowing through the one electronic switch when the current flowing through the inductor throughout the duty cycle is substantially continuous.

13. The circuit of claim 12 wherein the computation circuit is configured to compute the efficiency of the DC-DC converter based on the stored value of the internal DC resistance of the switching inductor or other element during a duty cycle when the current flowing through the inductor throughout the duty cycle is substantially discontinuous.

14. The circuit of claim 1 wherein the computation circuit is configured to compute the efficiency of the DC-DC converter without utilizing a signal indicative of the voltage across a sense resistor connected in series with the output of the DC-DC converter.

15. The circuit of claim 1 wherein the computation circuit is configured to compute the efficiency of the DC-DC converter without a known load current.

16. The circuit of claim 15 wherein the computation circuit is configured to compute the efficiency of the DC-DC converter without utilizing a signal indicative of the voltage across a sense resistor connected in series with the output of the DC-DC converter.

17. The circuit of claim 1 wherein the DC-DC converter is a step up DC-DC converter.

18. The circuit of claim 17 wherein the DC-DC converter includes a catch diode functioning as an electronic switch and configured to control current through the inductor, and wherein the duty cycle circuit is configured to measure the duty cycle of current flowing through the catch diode.

19. The circuit of claim 1 wherein the computing circuit is configured to compute the internal DC resistance of the switching inductor or other element during a calibration mode different than when the DC-DC converter is normally operating.

20. The circuit of claim 1 wherein the computing circuit is configured to compute the internal DC resistance of the switching inductor or other element based in part on an average of the voltage drop across the inductor or other element and an average of the current through the one electronic switch.

21. The circuit of claim 1 wherein the computing circuit is configured to compute the internal DC resistance of the switching inductor or other element based in part on the temperature of the inductor or other element.

22. The circuit of claim 1 wherein the current sense circuit includes a sense resistor in series with the one switch.

23. The circuit of claim 1 wherein the DC-DC converter is a multi-phase DC-DC converter having a plurality of switching inductors and, for each, a plurality of electronic switches that control current the inductor, wherein:

the duty cycle circuit is configured to measure the duty cycle of current flowing through the electronic switches that controls current through each of the inductors;

the current sense circuit is configured to measure the current flowing through the electronic switches that control the currents through each of the inductors;

the inductor voltage sensor circuit is configured to measure the voltage across each of the inductors or across each of another element which has resistance and is in series with each inductor; and

the computation circuit configured to compute the;

internal DC resistance of each of the switching inductors based in part on the duty cycle and current of the electronic switch associated with that inductor measured by the duty cycle and current sense circuits.

24. The circuit of claim 1 wherein the voltage sensor circuit is configured to measure the voltage across the inductor.