Inductor current zero-crossing detection method and circuit and switching power supply thereof

• US 9,515,550 B2
• Filed: 12/09/2014
• Issued: 12/06/2016
• Est. Priority Date: 12/24/2013
• Status: Active Grant

• Current Assignee: Silergy Semiconductor Technology (Hangzhou) Ltd. (Silergy Corporation)
• Original Assignee: Silergy Semiconductor Technology (Hangzhou) Ltd. (Silergy Corporation)
• Inventors: Chen, Lei
• Primary Examiner(s): Berhane, Adolf
• Application Number:
  US14/564,815
• Publication Number:
  US 20150180339A1
• Time in Patent Office: 728 Days
• Field of Search: 323/235, 323/268, 323/269, 323/271, 323/274, 323/319
• US Class Current: 1/1
• 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 3/156 with automatic control of output voltage or current, e.g. switching regulators
• 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

In one embodiment, a method of detecting an inductor current zero-crossing in a switching power supply, can include: (i) determining a present output voltage of the switching power supply; (ii) generating a zero-crossing detection threshold voltage according to the output voltage; and (iii) generating a zero-crossing detection signal according to the zero-crossing detection threshold voltage, where the zero-crossing detection signal is used to turn off a synchronous rectifier switch in the switching power supply.

Claims

1. A method of detecting an inductor current zero-crossing in a switching power supply, the method comprising:

a) determining a present output voltage of said switching power supply;

b) generating a zero-crossing detection threshold voltage with a predetermined fixed value when said output voltage is less than or equal to a predetermined minimum output voltage; and

c) generating a zero-crossing detection signal according to said zero-crossing detection threshold voltage, wherein said zero-crossing detection signal is used to turn off a synchronous rectifier switch in said switching power supply, wherein said zero-crossing detection threshold voltage is generated to vary with said output voltage when said output voltage is greater than said predetermined minimum output voltage.

2. The method of claim 1, wherein said generating said zero-crossing detection threshold voltage to vary with said output voltage comprises generating said zero-crossing detection threshold voltage in a linear relationship with said output voltage.

3. The method of claim 1, wherein said generating said zero-crossing detection threshold voltage to vary with said output voltage comprises generating said zero-crossing detection threshold voltage to increase with said output voltage.

4. The method of claim 3, wherein said generating said zero-crossing detection signal according to said zero-crossing detection threshold voltage comprises comparing said zero-crossing detection threshold voltage against a zero voltage.

5. The method of claim 1, wherein said generating said zero-crossing detection threshold voltage to vary with said output voltage comprises generating said zero-crossing detection threshold voltage to decrease when said output voltage is increasing.

6. The method of claim 5, wherein said generating said zero-crossing detection signal according to said zero-crossing detection threshold voltage comprises comparing said zero-crossing detection threshold voltage against said output voltage.

7. A method of detecting an inductor current zero-crossing in a switching power supply, the method comprising:

a) determining a present output voltage of said switching power supply according to a present input voltage of said switching power supply and a duty cycle of a pulse-width modulation (PWM) signal, wherein said output voltage is equal to a product of said input voltage and said duty cycle;

b) generating a zero-crossing detection threshold voltage according to said output voltage; and

c) generating a zero-crossing detection signal according to said zero-crossing detection threshold voltage, wherein said zero-crossing detection signal is used to turn off a synchronous rectifier switch in said switching power supply.

8. An inductor current zero-crossing detection circuit configured in a switching power supply, the circuit comprising:

a) an output voltage sampling circuit configured to determine a present output voltage of said switching power supply;

b) a zero-crossing detection threshold voltage generating circuit configured to generate a zero-crossing detection threshold voltage with a predetermined fixed value when said output voltage is less than or equal to a predetermined minimum output voltage; and

c) a zero-crossing detection circuit configured to generate a zero-crossing detection signal according to said zero-crossing detection threshold voltage, wherein said zero-crossing detection signal is used to turn off a synchronous rectifier switch in said switching power supply, and wherein said zero-crossing detection threshold voltage is generated to vary with said output voltage when said output voltage is greater than said predetermined minimum output voltage.

9. The circuit of claim 8, wherein said zero-crossing detection threshold voltage varies with said output voltage by a linear relationship with said output voltage.

10. The circuit of claim 8, wherein said zero-crossing detection threshold voltage varies with said output voltage by increasing with said output voltage.

11. The circuit of claim 10, further comprising:

a) a zero-crossing comparator having a first input terminal coupled to an output terminal of said zero-crossing detection threshold voltage generating circuit, and a second input terminal coupled to ground;

b) a first voltage controlled current source configured to provide a variable current that increases along with said output voltage when said output voltage is greater than said minimum output voltage;

c) a first constant current source and said first voltage controlled current source being coupled to said first input terminal; and

d) a first switch coupled between a first node and said first input terminal, wherein said first switch is controllable by a pulse-width modulation (PWM) signal, and wherein a main power switch and an inductor of said switching power supply are coupled at said first node.

12. The circuit of claim 8, wherein said zero-crossing detection threshold voltage varies with said output voltage by decreasing when said output voltage increases.

13. The circuit of claim 12, further comprising:

a) a zero-crossing comparator having a second input terminal coupled to an output terminal of said zero-crossing detection threshold voltage generating circuit, and a first input terminal coupled to an output terminal of said switching power supply;

b) a second voltage controlled current source configured to provide a variable current that increases along with said output voltage when said output voltage is greater than said minimum output voltage;

c) a second constant current source and said second voltage controlled current source being coupled to said second input terminal; and

d) a second switch coupled between a first node and a second input terminal of said zero-crossing comparator, wherein said second switch is controllable by said PWM signal, and wherein a main power switch and an inductor of said switching power supply are coupled at said first node.

15. A switching power supply, comprising:

a) said inductor current zero-crossing detection circuit of claim 8; and

b) a power converter.

14. An inductor current zero-crossing detection circuit configured in a switching power supply, the circuit comprising:

a) an output voltage sampling circuit configured to determine a present output voltage of said switching power supply;

b) a zero-crossing detection threshold voltage generating circuit configured to generate a zero-crossing detection threshold voltage according to said output voltage;

c) a zero-crossing detection circuit configured to generate a zero-crossing detection signal according to said zero-crossing detection threshold voltage, wherein said zero-crossing detection signal is used to turn off a synchronous rectifier switch in said switching power supply;

d) an input current generating circuit having an input terminal coupled to a voltage input terminal of said switching power supply, and an output terminal coupled to a first terminal of a third switch; and

e) a sampling resistor having a first terminal coupled to a second terminal of said third switch, and a second terminal of said sampling resistor being coupled to ground, wherein said third switch is controllable by said PWM signal.