# US 2008/0186007 A1 · Power supply switch circuit with current leakage protection

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- Number: US 2008/0186007 A1
- Document ID: US20080186007A1
- Status: Published application
- Kind: A1
- Application number: 12/078,493
- Filed: 2008-04-01
- Published: 2008-08-07
- Earliest claimed: 2005-08-16
- Assignees: Universal Scientific Industrial Co., Ltd.
- Inventors: Yung-Fa Chen
- Web page: https://patentgrep.com/patent/US20080186007A1

## CPC

- H03K 17/302: {in field-effect transistor switches}
- H03K 17/16: Modifications for eliminating interference voltages or currents
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)

## Abstract

A power supply switch circuit with current leakage protection is used in an electronic device, and is able to prevent the erroneous actions caused by a leakage current in high-temperature environments. The power supply switch circuit comprises a transistor having an emitter, a base and a collector, a field effect transistor having a drain, a source and a gate, and at least two series-connected diodes. The emitter is connected to a voltage source. The collector is connected to a load via a forward biased diode. The drain receives a trigger signal. The source is connected a reference terminal via at least two series-connected diodes. The gate is connected to the collector via a second resistor. One terminal of a third resistor is connected to the gate, and the other terminal is connected to the reference terminal.

## Claims

### Claim 1

An electronic device receives a start signal for the activation of power supply, comprising:
a first switch unit receiving the start signal and outputting a trigger signal;
a PNP transistor connected to the first switch unit and conducted by the trigger signal;
a voltage divider unit connected to said PNP transistor and used to output a control bias according to a conduction current of said PNP transistor;
an N-channel field effect transistor connected to said PNP transistor and said voltage divider unit, conduction of said N-channel field effect transistor being controlled by said control bias and used to maintain said PNP transistor in an on state; and
a voltage clamp unit connected to said N-channel field effect transistor and providing a reference voltage to increase the level of an ON voltage of said N-channel field effect transistor;
a microprocessor; and
a second switch unit connected to the microprocessor, wherein the second switch receives the start signal and controls the microprocessor to turn on the N-channel field effect transistor via a third switch unit.

### Claim 2 (depends on 1)

The electronic device as claimed in claim 1, wherein said N-channel field effect transistor is connected to said PNP transistor via a first resistor.

### Claim 3 (depends on 2)

The electronic device as claimed in claim 2, wherein said voltage divider unit comprises a second resistor and a third resistor being connected in series relation.

### Claim 4 (depends on 3)

The electronic device as claimed in claim 3 further comprising a capacitor and a fourth resistor, wherein said capacitor and said fourth resistor are connected in parallel relation between an emitter and a base of said PNP transistor.

### Claim 5 (depends on 4)

The electronic device as claimed in claim 4, wherein said voltage clamp unit comprises at least two diodes, and said diodes are connected in series relation.

### Claim 6 (depends on 1)

The electronic device as claimed in claim 1, further comprising a load and a voltage regulator connected to the PNP transistor for receiving the voltage source respectively.