SWITCHED-MODE POWER SUPPLY

• US 20120274301A1
• Filed: 04/27/2012
• Published: 11/01/2012
• Est. Priority Date: 04/28/2011
• Status: Active Grant

• Current Assignee: Mitsumi Electric Co., Ltd. (Minebea Mitsumi, Inc.)
• Original Assignee: Mitsumi Electric Co., Ltd. (Minebea Mitsumi, Inc.)
• Inventors: NAKASHIMA, Heisuke
• Granted Patent: US 9,030,177 B2
• Time in Patent Office: Days
• US Class Current: 323/284
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 1/14 Arrangements for reducing ripples from dc input or output
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• 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 ripple-control switched-mode power supply includes a control circuit to switch on/off a drive switching element. The control circuit includes a simulated voltage generation circuit that smoothes a voltage at a node connecting the drive switching element and an inductor and that generates a simulated voltage corresponding to an output voltage; a timer that measures a time corresponding to an input voltage and the simulated voltage; a voltage comparison circuit that compares a feedback voltage and a predetermined voltage; and a control pulse generation circuit that generates a control pulse having a pulse width corresponding to the time based on outputs from the timer and the voltage comparison circuit. The control circuit varies the pulse width of the control pulse in accordance with a variation in the input voltage to maintain a constant switching cycle.

Claims

1. A switched-mode power supply that outputs a voltage different from an input voltage, the switched-mode power supply comprising:

an inductor connected between a voltage input terminal to which a DC voltage is input and an output terminal to which a load is connected;

a drive switching element that causes a current to intermittently flow through the inductor; and

a control circuit that is provided on a semiconductor chip as a semiconductor integrated circuit and that generates a drive pulse in response to the voltage input to the voltage input terminal and a feedback voltage from the output terminal to switch on/off the drive switching element, wherein

the control circuit comprises;

a simulated voltage generation circuit that smoothes a voltage at a node connecting the drive switching element and the inductor and that generates and outputs a simulated voltage corresponding to the output voltage;

a timer that measures a time corresponding to the input voltage and the simulated voltage;

a voltage comparison circuit that compares the feedback voltage and a predetermined voltage; and

a control pulse generation circuit that generates a control pulse having a pulse width corresponding to the time measured by the timer based on output from the timer and output from the voltage comparison circuit, and wherein

the control circuit varies the pulse width of the control pulse in accordance with a variation in the input voltage and the simulated voltage and outputs the drive pulse corresponding to the control pulse to maintain a constant switching cycle.

2. The switched-mode power supply according to claim 1, wherein the simulated voltage generation circuit comprises:

a voltage-dividing circuit that divides the voltage at the node connecting the drive switching element and the inductor; and

a filter circuit that smoothes the voltage divided by the voltage-dividing circuit.

3. The switched-mode power supply according to claim 2, wherein

the timer comprises:

a waveform generation circuit that generates a waveform signal having an inclination corresponding to the input voltage; and

a voltage comparison circuit that compares the waveform signal generated in the waveform generation circuit with the simulated voltage, and wherein

the filter circuit has a time constant to generate the simulated voltage that has an amplitude of 1/100 or less of an amplitude of the waveform signal generated in the waveform generation circuit.

4. The switched-mode power supply according to claim 3, wherein

the control circuit has a soft-start function, and

the time constant of the filter circuit is set such that a rising time of the simulated voltage is shorter than a rising time of the output voltage at start-up.

5. The switched-mode power supply according to claim 1, wherein

the drive switching element is an N-channel MOS transistor, and

the control circuit has external terminals to which a source terminal of the MOS transistor and the inductor are connected.

6. The switched-mode power supply according to claim 2, wherein

the drive switching element is an N-channel MOS transistor, and

the control circuit has external terminals to which a source terminal of the MOS transistor and the inductor are connected.

7. The switched-mode power supply according to claim 3, wherein

the drive switching element is an N-channel MOS transistor, and

the control circuit has external terminals to which a source terminal of the MOS transistor and the inductor are connected.

8. The switched-mode power supply according to claim 4, wherein

the drive switching element is an N-channel MOS transistor, and

the control circuit has external terminals to which a source terminal of the MOS transistor and the inductor are connected.