# US 9,520,770 B2 · Soft start circuit

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- Number: US 9,520,770 B2
- Document ID: US9520770B2
- Status: Granted
- Kind: B2
- Application number: 14/827,554
- Filed: 2015-08-17
- Published: 2016-02-18
- Granted: 2016-12-13
- Earliest claimed: 2014-08-18
- Assignees: Rohm Co., Ltd.
- Applicants: Rohm Co., Ltd.
- Inventors: Ryosuke Sumii; Kiminobu Sato
- Web page: https://patentgrep.com/patent/US9520770B2

## CPC

- H02M 1/36: Means for starting or stopping converters
- H02M 3/156: with automatic control of output voltage or current, e.g. switching regulators
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)

## Abstract

A soft start circuit accepts an input of a reference voltage set arbitrarily, and generates a soft start voltage that takes a predetermined sweep time to slowly rise from a predetermined lowest value to a highest value that is higher than the reference voltage and changes in accordance with the reference voltage.

## Claims

### Claim 1

A soft start circuit used in a power source apparatus, wherein
the soft start circuit accepts an input of a reference voltage set arbitrarily, and generates a soft start voltage that takes a predetermined sweep time to slowly rise from a predetermined lowest value to a highest value that is higher than the reference voltage and changes in accordance with the reference voltage, and
the soft start circuit comprises:
a digital/analog converter that is supplied with the reference voltage as a power source voltage, and converts a digital sweep signal, which is increased at a constant period from a minimum value to a maximum value, into an analog sweep voltage, and
a voltage amplification portion that amplifies the analog sweep voltage by using a predetermined gain and thereby generates the soft start voltage.

### Claim 2 (depends on 1)

A power source apparatus comprising:
the soft start circuit according to claim 1,
an error amplifier that generates an error voltage in accordance with a difference between a feedback voltage and a lower one of the reference voltage and the soft start voltage,
a DC/DC converter that generates an output voltage from an input voltage in accordance with the error voltage, and
a feedback voltage generation portion that generates the feedback voltage in accordance with the output voltage.

### Claim 3 (depends on 2)

The power source apparatus according to claim 2, further comprising
a reference voltage generation circuit that generates the reference voltage.

### Claim 4 (depends on 3)

The power source apparatus according to claim 3, wherein
the reference voltage generation circuit includes:
a second digital/analog converter that converts a digital reference signal set arbitrarily into an analog reference voltage, and
a second voltage amplification portion that amplifies the analog reference voltage by using a predetermined gain and thereby generates the reference voltage.

### Claim 5 (depends on 4)

The power source apparatus according to claim 4, further comprising
a logic circuit that generates at least one of the digital sweep signal and the digital reference signal.

### Claim 6 (depends on 5)

The power source apparatus according to claim 5, wherein
the logic circuit generates the digital reference signal to raise the reference voltage at a time when the power source apparatus is enabled, thereafter, generates the digital sweep signal to raise the soft start voltage at a time when the DC/DC converter becomes operable.

### Claim 7 (depends on 2)

The power source apparatus according to claim 2, further comprising
an external terminal for accepting an external input of the reference voltage.

### Claim 8 (depends on 2)

An electronic apparatus comprising:
the power source apparatus according to claim 2, and
a load that is supplied with an output voltage from the power source apparatus to operate.