Soft-start circuit for buck converter control

• US 10,491,117 B2
• Filed: 06/29/2016
• Issued: 11/26/2019
• Est. Priority Date: 06/29/2015
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Moon, SangCheol, Koo, Gwanbon, Jin, Chenghao, Chung, Bonggeun
• Primary Examiner(s): Ahmed, Yusef A
• Assistant Examiner(s): Singh, David A.
• Application Number:
  US15/196,559
• Publication Number:
  US 20160380541A1
• Time in Patent Office: 1,245 Days
• CPC Class Codes: G01R 19/04 Measuring peak values or amplitude or envelope of ac or of pulses
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• CPC Class Codes: H02M 1/0054 Transistor switching losses periodically suspending operation of switching converter in low power mode H02M1/0035
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A buck converter includes a power switch having a first end to receive an input voltage, and a soft start circuit configured to compensate a soft start voltage during a soft start time period according to a result of comparing a feedback voltage corresponding to an output voltage of the buck converter and an input detection voltage corresponding to the input voltage. The buck converter controls switching of the power switch using the soft start voltage.

Claims

1. A switch control circuit for a power switch coupled to an inductor between an input terminal and an output terminal in a converter circuit, the switch control circuit comprising:

a soft start circuit configured to compensate a soft start voltage during a soft start time period by;

comparing a feedback voltage corresponding to an output voltage of the output terminal to an input detection voltage corresponding to an input voltage of the input terminal,

causing the soft start voltage to increase at a first slope in response to the feedback voltage being lower than the input detection voltage, and

causing the soft start voltage to change according to a second slope different from the first slope in response to the feedback voltage being higher than the input detection voltage; and

a circuit configured to control switching of the power switch by using the soft start voltage and the feedback voltage during the soft start time period,

wherein the input voltage is an Alternating Current (AC) voltage, and

wherein the input detection voltage is a rectified AC voltage.

2. The switch control circuit of claim 1, wherein the soft start circuit is configured to decrease the soft start voltage during the soft start time period when the feedback voltage is higher than the input detection voltage.

3. The switch control circuit of claim 2, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a first transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated; and

a current sink coupled to a second end of the first transistor.

4. The switch control circuit of claim 3, wherein the soft start circuit further comprises a current source coupled to the capacitor.

5. The switch control circuit of claim 4, wherein the soft start circuit further comprises a second transistor configured to perform switching according to the output of the comparator and coupled between the capacitor and the current source.

6. The switch control circuit of claim 1, wherein the soft start circuit is configured to maintain the soft start voltage at a constant level during the soft start time period when the feedback voltage is higher than the input detection voltage.

7. The switch control circuit of claim 6, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated; and

a current source coupled to a second end of the transistor.

8. The switch control circuit of claim 1, wherein the soft start circuit is configured to increase the soft start voltage at the second slope during the soft start time period when the feedback voltage is higher than the input detection voltage, wherein the first slope is greater than the second slope.

9. The switch control circuit of claim 8, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a first transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated;

a first current source coupled to a second end of the first transistor;

a second transistor configured to perform switching according to the output of the comparator and having a first end coupled to the capacitor; and

a second current source coupled to a second end of the second transistor.

10. The switch control circuit of claim 9, wherein the first transistor and the second transistor have different channel types.

11. A buck converter comprising:

a power switch having a first end to receive an input voltage; and

a soft start circuit configured to compensate a soft start voltage during a soft start time period by;

comparing a feedback voltage corresponding to an output voltage of the buck converter and an input detection voltage corresponding to the input voltage,

causing the soft start voltage to increase at a first slope in response to the feedback voltage being lower than the input detection voltage, and

causing the soft start voltage to change at a second slope different from the first slope in response to the feedback voltage being higher than the input detection voltage,

wherein the buck converter controls switching of the power switch using the soft start voltage,

wherein the input voltage is an Alternating Current (AC) voltage, and

wherein the input detection voltage is a rectified AC voltage.

12. The buck converter of claim 11, wherein the soft start circuit is configured to decrease the soft start voltage during the soft start time period when the feedback voltage is higher than the input detection voltage.

13. The buck converter of claim 12, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a first transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated; and

a current sink coupled to a second end of the first transistor.

14. The buck converter of claim 13, wherein the soft start circuit further comprises a current source coupled to the capacitor.

15. The buck converter of claim 14, wherein the soft start circuit further comprises a second transistor configured to perform switching according to the output of the comparator and coupled between the capacitor and the current source.

16. The buck converter of claim 11, wherein the soft start circuit is configured to maintain the soft start voltage at a constant level during the soft start time period when the feedback voltage is higher than the input detection voltage.

17. The buck converter of claim 16, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated; and

a current source coupled to a second end of the transistor.

18. The buck converter of claim 11, wherein the soft start circuit is configured to increase the soft start voltage at the second slope during the soft start time period when the feedback voltage is higher than the input detection voltage, wherein the first slope is greater than the second slope.

19. The buck converter of claim 18, wherein the soft start circuit comprises:

a comparator configured to compare the feedback voltage and the input detection voltage;

a first transistor configured to perform switching according to an output of the comparator and having a first end coupled to a capacitor by which the soft start voltage is generated;

a first current source coupled to a second end of the first transistor;

a second transistor configured to perform switching according to the output of the comparator and having a first end coupled to the capacitor; and

a second current source coupled to a second end of the second transistor.

20. The buck converter of claim 19, wherein the first transistor and the second transistor have different channel types.