Power supply circuit

• US 8,947,062 B2
• Filed: 08/10/2011
• Issued: 02/03/2015
• Est. Priority Date: 08/20/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Ohmaru, Takuro
• Primary Examiner(s): Han, Jessica
• Application Number:
  US13/206,819
• Publication Number:
  US 20120043953A1
• Time in Patent Office: 1,273 Days
• Field of Search: 323282-285
• US Class Current: 323/283
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

In the case where the duty cycle of the PWM signal exists and the duty cycle of the PWM signal is constant for a certain period, a feedback control circuit is operated intermittently with the duty cycle fixed. Specifically, a power supply circuit includes an A/D converter circuit for forming a digital value based on an analog value obtained by monitoring an output voltage based on a reference voltage, a digital filter circuit for smoothing the digital value, a PWM signal generator circuit for generating a PWM signal based on an output value of the digital filter circuit, and an operation mode control circuit for controlling a circuit operation mode based on the duty cycle of the PWM signal.

Claims

1. A power supply circuit comprising:

an A/D converter circuit for forming a digital value in accordance with an output voltage based on a reference voltage;

a digital filter circuit for smoothing the digital value;

a PWM signal generator circuit for generating a PWM signal based on an output value of the digital filter circuit; and

an operation mode control circuit for controlling a circuit operation mode based on a duty cycle of the PWM signal,

wherein the operation mode control circuit comprises a clock gating circuit, and

wherein the clock gating circuit is configured to stop supply of a clock signal to the A/D converter circuit and the digital filter circuit in an operation mode where the duty cycle of the PWM signal is fixed to be constant.

2. The power supply circuit according to claim 1, wherein the clock gating circuit comprises an AND circuit and an inverter circuit electrically connected to one input terminal of the AND circuit.

3. A power supply circuit comprising:

an A/D converter circuit for forming a digital value in accordance with an output voltage based on a reference voltage;

a digital filter circuit for smoothing the digital value;

a PWM signal generator circuit for generating a PWM signal based on an output value of the digital filter circuit;

an operation mode control circuit for controlling a circuit operation mode based on a duty cycle of the PWM signal; and

a circuit for outputting, in a case where the duty cycle of the PWM signal is fixed to be constant, a flag signal by detecting that the duty cycle of the PWM signal is fixed to be constant,

wherein the operation mode control circuit is configured to control based on the flag signal, a first operation mode in which the duty cycle of the PWM signal is fixed and a second operation mode in which the duty cycle is variable,

wherein the operation mode control circuit comprises a clock gating circuit, and

wherein the clock gating circuit is configured to stop supply of a clock signal to the A/D converter circuit and the digital filter circuit in the first operation mode where the duty cycle of the PWM signal is fixed to be constant.

4. The power supply circuit according to claim 3, wherein the clock gating circuit comprises an AND circuit and an inverter circuit electrically connected to one input terminal of the AND circuit.

5. A power supply circuit comprising:

an A/D converter circuit for forming a digital value in accordance with an output voltage based on a reference voltage;

a digital filter circuit for smoothing the digital value;

a PWM signal generator circuit for generating a PWM signal based on an output value of the digital filter circuit; and

an operation mode control circuit for controlling a circuit operation mode based on a duty cycle of the PWM signal

a voltage converter circuit comprising;

an input terminal;

a coil electrically connected to the input terminal;

a diode, wherein one terminal of the diode is electrically connected to the coil;

a transistor, wherein one terminal of the transistor is electrically connected to the coil and the one terminal of the diode; and

an output terminal electrically connected to the other terminal of the diode;

wherein the PWM signal generator circuit is electrically connected to a gate of the transistor,

wherein the A/D converter circuit is electrically connected to the output terminal with a resistor interposed therebetween,

wherein the operation mode control circuit comprises a clock gating circuit, and

wherein the clock gating circuit is configured to stop supply of a clock signal to the A/D converter circuit and the digital filter circuit during the duty cycle of the PWM signal being fixed to be constant.

6. The power supply circuit according to claim 5, wherein the clock gating circuit comprises:

an inverter; and

an AND circuit having;

a first input terminal electrically connected to the gate of the transistor;

a second input terminal electrically connected to the inverter; and

an output terminal electrically connected to the A/D converter circuit and the digital filter circuit.

7. A method for driving a power supply circuit, comprising the steps of:

detecting that an output of a digital filter circuit is fixed to be constant;

outputting a flag signal from the digital filter circuit to an operation mode control circuit by detecting that the output of the digital filter circuit is fixed to be constant;

stopping supply of a clock signal to the digital filter circuit and an A/D converter circuit in accordance with the flag signal, wherein the A/D converter circuit is configured to output a digital signal to the digital filter circuit in accordance with an input of an analog signal to the A/D converter circuit.

8. The method for driving a power supply circuit according to claim 7,

wherein a duty cycle of a PWM signal output from a PWM generator circuit is constant during the supply of the clock signal being stopped, and

wherein the PWM generator circuit is electrically connected to the digital filter circuit and the operation mode control circuit.