DC/DC Converter and Current Sense Circuit Thereof

• US 20100052632A1
• Filed: 09/04/2008
• Published: 03/04/2010
• Est. Priority Date: 09/04/2008
• Status: Active Grant

• Current Assignee: Himax Analogic, Inc. (Himax Technologies Incorporated)
• Original Assignee: Himax Analogic, Inc. (Himax Technologies Incorporated)
• Inventors: Wu, Kuo-Hung
• Granted Patent: US 8,054,059 B2
• Time in Patent Office: Days
• US Class Current: 323/272
• 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

A current sense circuit includes a power transistor, a first level shifter, an operational transconductance amplifier (OTA), a second level shifter, and a dummy transistor. The power transistor has a first terminal and a power control terminal coupled to a control voltage. The first level shifter is coupled to the first terminal and pulls up a voltage of the first terminal to an operating voltage. The OTA is coupled to the first level shifter and converts the operating voltage into an operating current. The second level shifter is coupled to the OTA and pulls down the operating voltage to the voltage of the first terminal. The dummy transistor has a dummy control terminal with the control voltage, and a third terminal coupled to the second level shifter and having the same voltage as the voltage of the first terminal.

Claims

1. A current sense circuit, comprising:

a power transistor having a first terminal, a second terminal coupled to a first power voltage, and a power control terminal coupled to a control voltage;

a first level shifter coupled to the first terminal and pulling up a voltage of the first terminal to an operating voltage;

an operational transconductance amplifier (OTA) coupled to the first level shifter and converting the operating voltage into an operating current;

a second level shifter coupled to the OTA and pulling down the operating voltage to the voltage of the first terminal; and

a dummy transistor having a dummy control terminal with the control voltage, a third terminal coupled to the second level shifter and having the same voltage as the voltage of the first terminal, and a fourth terminal coupled to the first power voltage.

2. The current sense circuit as claimed in claim 1, wherein the power transistor is multiple times the size of the dummy transistor.

3. The current sense circuit as claimed in claim 1, wherein the power transistor is made of multiple of the dummy transistors connected in parallel.

4. The current sense circuit as claimed in claim 2 or 3, wherein a current flowing through the power transistor is multiple times the value of another current flowing through the dummy transistor.

5. The current sense circuit as claimed in claim 1, wherein the OTA further comprises:

a differential pair circuit current biased by a current source and having a pair of differential inputs having the same voltage, one of the differential inputs being coupled to the operating voltage pulled up by the first level shifter.

6. The current sense circuit as claimed in claim 5, wherein the OTA further comprises:

a first current mirror coupled to the differential pair circuit such that differential currents flowing through the differential pair circuit being the same and the differential inputs having the same voltage.

7. The current sense circuit as claimed in claim 6, wherein the differential pair circuit further comprises:

a first BJT having a first base as one of the differential inputs, a third terminal coupled to the first current mirror, and a fourth terminal coupled to the current source; and

a second BJT having a second base as the other of the differential inputs, a fifth terminal coupled to the first current mirror, and a sixth terminal coupled to the current source.

8. The current sense circuit as claimed in claim 7, wherein the first current mirror further comprises:

a first MOS transistor having a seventh terminal coupled to a second power voltage, and an eighth terminal and a first control terminal both coupled to the third terminal of the first BJT; and

a second MOS transistor having a second control terminal coupled to the first control terminal, a ninth terminal coupled to the second power voltage, and a tenth terminal coupled to the fifth terminal of the second BJT.

9. The current sense circuit as claimed in claim 5, wherein the first level shifter further comprises:

a third MOS transistor having a third control terminal coupled to the first terminal of the power transistor, an eleventh terminal coupled to one of the differential inputs, and a twelfth terminal coupled to the first power voltage.

10. The current sense circuit as claimed in claim 9, wherein the second level shifter further comprises:

a fourth MOS transistor having a thirteenth terminal coupled to the other of the differential inputs, and a fourth control terminal and a fourteenth terminal both coupled to the third terminal of the dummy transistor.

11. The current sense circuit as claimed in claim 1, further comprising:

a second current mirror mirroring the operating current to the first level shifter for pulling up the voltage of the first terminal of the power transistor to the operating voltage.

12. A DC/DC converter, comprising:

a control circuit outputting a pulse drive signal;

a switch activated by the pulse drive signal, such that an inductor is charged by an input voltage to deliver an inducting current; and

a current sense circuit sensing the inducting current to output a current sense signal to be superimposed by a slope compensation signal output by a slope compensation circuit, the superimposition of the current sense signal and the slope compensation signal being transformed into a feedback signal for controlling the control circuit, the current sense circuit comprising;

a power transistor having a first terminal, a second terminal coupled to a first power voltage, and a power control terminal coupled to a control voltage;

a first level shifter coupled to the first terminal and pulling up a voltage of the first terminal to an operating voltage;

an operational transconductance amplifier (OTA) coupled to the first level shifter and converting the operating voltage into an operating current;

a second level shifter coupled to the OTA and pulling down the operating voltage to the voltage of the first terminal; and

a dummy transistor having a dummy control terminal with the control voltage, a third terminal coupled to the second level shifter and having the same voltage as the voltage of the first terminal, and a fourth terminal coupled to the first power voltage.

13. The DC/DC converter as claimed in claim 12, wherein the power transistor is multiple times the size of the dummy transistor.

14. The DC/DC converter as claimed in claim 12, wherein the power transistor is made of multiple of the dummy transistors connected in parallel.

15. The DC/DC converter as claimed in claim 13 or 14, wherein a current flowing through the power transistor is multiple times the value of another current flowing through the dummy transistor.

16. The DC/DC converter as claimed in claim 12, wherein the OTA further comprises:

a differential pair circuit current biased by a current source and having a pair of differential inputs having the same voltage, one of the differential inputs being coupled to the operating voltage pulled up by the first level shifter.

17. The DC/DC converter as claimed in claim 16, wherein the OTA further comprises:

a first current mirror coupled to the differential pair circuit such that differential currents flowing through the differential pair circuit being the same and the differential inputs having the same voltage.

18. The DC/DC converter as claimed in claim 17, wherein the differential pair circuit further comprises:

a first BJT having a first base as one of the differential inputs, a third terminal coupled to the first current mirror, and a fourth terminal coupled to the current source; and

a second BJT having a second base as the other of the differential inputs, a fifth terminal coupled to the first current mirror, and a sixth terminal coupled to the current source.

19. The DC/DC converter as claimed in claim 18, wherein the first current mirror further comprises:

a first MOS transistor having a seventh terminal coupled to a second power voltage, and an eighth terminal and a first control terminal both coupled to the third terminal of the first BJT; and

a second MOS transistor having a second control terminal coupled to the first control terminal, a ninth terminal coupled to the second power voltage, and a tenth terminal coupled to the fifth terminal of the second BJT.

20. The DC/DC converter as claimed in claim 16, wherein the first level shifter further comprises:

a third MOS transistor having a third control terminal coupled to the first terminal of the power transistor, an eleventh terminal coupled to one of the differential inputs, and a twelfth terminal coupled to the first power voltage.

21. The DC/DC converter as claimed in claim 20, wherein the second level shifter further comprises:

a fourth MOS transistor having a thirteenth terminal coupled to the other of the differential inputs, and a fourth control terminal and a fourteenth terminal both coupled to the third terminal of the dummy transistor.

22. The DC/DC converter as claimed in claim 12, further comprising:

a second current mirror mirroring the operating current to the first level shifter for pulling up the voltage of the first terminal of the power transistor to the operating voltage.