US20070040452A1 - Power supply switch circuit with current leakage protection - Google Patents

Power supply switch circuit with current leakage protection Download PDF

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Publication number
US20070040452A1
US20070040452A1 US11/330,158 US33015806A US2007040452A1 US 20070040452 A1 US20070040452 A1 US 20070040452A1 US 33015806 A US33015806 A US 33015806A US 2007040452 A1 US2007040452 A1 US 2007040452A1
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transistor
power supply
switch circuit
supply switch
field effect
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US11/330,158
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Yung-fa Chen
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Universal Scientific Industrial Co Ltd
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Universal Scientific Industrial Co Ltd
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Assigned to UNIVERSAL SCIENTIFIC INDUSTRIAL CO., LTD. reassignment UNIVERSAL SCIENTIFIC INDUSTRIAL CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHEN, YUNG-FA
Publication of US20070040452A1 publication Critical patent/US20070040452A1/en
Priority to US12/078,493 priority Critical patent/US7474085B2/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/30—Modifications for providing a predetermined threshold before switching
    • H03K17/302—Modifications for providing a predetermined threshold before switching in field-effect transistor switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/16—Modifications for eliminating interference voltages or currents

Definitions

  • the present invention relates to a power supply switch circuit with current leakage protection and, more particularly, to a circuit used in an electronic device and capable of preventing the erroneous actions caused by a circuit leakage current in high temperature environments.
  • a prior art power supply switch circuit is primarily formed by connecting two transistors Q 1 , Q 2 and other electronic components.
  • a trigger signal S T is used to control the transistor Q 1 to be on so that a voltage source V CC can provide power to a load 90 via the transistor Q 1 .
  • the supplied power can also be sent to the base of the transistor Q 2 to make the transistor Q 2 on.
  • the base of the transistor Q 1 will be connected to a reference terminal Gnd to keep the transistor Q 1 on.
  • a controller 91 will send a cut-off signal to the transistor Q 2 to make the transistor Q 2 off.
  • the transistor Q 1 will then be off in succession so that the voltage source V CC can no longer provide power to the load 90 .
  • the leakage current of a transistor depends on the working temperature.
  • the magnitude of the leakage current is proportional to temperature. Please refer to FIG. 1 again.
  • the transistor Q 2 will have a leakage current I CEO .
  • the leakage current I CEO increases, and the base current I B1 flowing through the transistor Q 1 increases therewith.
  • the collector current I C is ⁇ times the base current I B according to the transistor's characteristics, the collector current I C1 of the transistor Q 1 will increase with the base current I B1 of the transistor Q 1 .
  • the base current I B2 of the transistor Q 2 increases with the collector current I C1 of the transistor Q 1 .
  • the leakage current I CEO increases.
  • the power supply switch circuit will generate erroneous actions. That is, when the power supply switch circuit is originally in the off state (i.e., stops providing power), the transistor Q 1 will be on due to the leakage current I CEO to drive the power supply switch circuit into the on state (i.e., starts providing power).
  • An object of the present invention is to provide a power supply switch circuit with current leakage protection, which is used in an electronic device and capable of preventing the erroneous actions caused by a circuit leakage current in high temperature environments.
  • the present invention comprises a transistor, a field effect transistor and a third resistor.
  • the transistor has an emitter, a base and a collector. The emitter is connected to a voltage source. The collector is connected to a load via a forward biased diode.
  • the field effect transistor has a drain, a source and a gate. The drain receives a trigger signal. The source is connected to a reference terminal via at least two series-connected diodes. The gate is connected to the collector via a second resistor. One terminal of the third resistor is connected to the gate, and the other terminal is connected to the reference terminal.
  • FIG. 1 is a circuit diagram of a prior art power supply switch circuit
  • FIG. 2 is a circuit diagram of a power supply switch circuit with current leakage protection of the present invention.
  • FIG. 3 is a circuit diagram showing how the present invention is used in an electronic device.
  • FIG. 2 is a circuit diagram of a power supply switch circuit with current leakage protection of the present invention.
  • the power supply switch circuit with current leakage protection is used in an electronic device (not shown), and can prevent the erroneous actions caused by a leakage current in high temperature environments.
  • the power supply switch circuit with current leakage protection comprises a transistor Q 3 , a field effect transistor Q 4 and a third resistor R 14 .
  • the transistor Q 3 has an emitter E, a base B and a collector C.
  • the emitter E is connected to a voltage source V CC .
  • the collector C is connected to a load 92 via a forward biased diode D 13 .
  • the field effect transistor Q 4 has a drain D, a source S and a gate G.
  • the drain D is connected to the base B of the transistor Q 3 via a first resistor R 12 , and receives a trigger signal S T1 .
  • the source S is connected to a reference terminal Gnd via a voltage clamp unit 93 .
  • the voltage clamp unit 93 provides a reference voltage, and is formed by series connecting at least two diodes (D 11 , D 12 ) together in this embodiment.
  • the gate is connected to the collector C of the transistor Q 3 via a second resistor R 13 .
  • One terminal of the third resistor R 14 is connected to the gate G of the field effect transistor Q 4 , and the other terminal is connected to the reference terminal Gnd.
  • the second resistor R 13 and the third resistor R 14 are series connected together to form a voltage divider unit 94 .
  • the power supply switch circuit with current leakage protection of the present invention further comprises a capacitor C 11 and a fourth resistor R 11 , which are parallel connected between the emitter E and the base B of the transistor Q 3 .
  • the transistor Q 3 is a PNP transistor
  • the field effect transistor Q 4 is an N-channel field effect transistor.
  • the power supply switch circuit When the power supply switch circuit supplies power normally, it receives a low-level trigger signal S T1 for the activation of power supply.
  • the low-level trigger signal S T1 drives the transistor Q 3 to be on.
  • the voltage source V CC After the transistor Q 3 is on, the voltage source V CC provides power to the load 92 via the transistor Q 3 . Because the transistor Q 3 is on, the voltage source V CC will produce a large enough control bias on the resistor R 14 of the voltage divider unit 94 to drive the field effect transistor Q 4 to be on.
  • the control bias is larger than the sum of the on voltage of the field effect transistor Q 4 and the reference voltage, the field effect transistor Q 4 immediately enters the on state. After the field effect transistor Q 4 is on, the base B of the transistor Q 3 is connected to the reference terminal Gnd to keep the transistor Q 3 on, thereby continuing providing power to the load 92 .
  • the field effect transistor Q 4 When the circuit stops providing power, the field effect transistor Q 4 will generates a leakage current I DSS . When the temperature rises, the leakage current I DSS increases, and the base current I B3 flowing through the transistor Q 3 increases therewith. Because the collector current I C is ⁇ times the base current I B according to the transistor's characteristics, the collector current I C3 of the transistor Q 3 will increase with the base current I B3 . The increase of the collector current I C3 of the transistor Q 3 will cause an increase in the voltage of the gate G of the field effect transistor Q 4 .
  • the source S of the field effect transistor Q 4 is series connected to the voltage clamp unit 93 (i.e., at least two series-connected diodes D 11 and D 12 ), for the field effect transistor Q 4 to be on, the voltage of the gate G has to be larger than the sum of the pinch-off voltage V T of the field effect transistor Q 4 and the voltage drop across the at least two series-connected diodes D 11 and D 12 .
  • the increase of the leakage current I DSS will lead the base current I B3 and the collector current I C3 of the transistor Q 3 to rise in succession.
  • the voltage of the gate of the field effect transistor Q 4 generated when the collector current I C3 flowing through the third resistor R 14 is still smaller than the sum of the pinch-off voltage V T of the field effect transistor Q 4 and the voltage drop across the at least two series-connected diodes D 11 and D 12 , the field effect transistor Q 4 won't cause erroneous actions even if there is any variation in temperature. Therefore, the power supply switch circuit can work stably without any influence from transistor's leakage current in high-temperature environments.
  • FIG. 3 is a circuit diagram showing how the present invention is used in an electronic device.
  • An electronic device 10 provides a high-level trigger signal S TR for the activation of power supply.
  • the high-level trigger signal S TR is connected to a power supply switch circuit 20 via a first switch unit 30 , and is connected to a microprocessor 50 via a second switch unit 40 .
  • the high-level trigger signal S TR drives a transistor Q 5 in the first switch unit 30 to be on. After the transistor Q 5 is on, the base of the transistor Q 3 is connected to the reference terminal Gnd so that the transistor Q 3 is on.
  • the voltage source V CC thus provides power to a load 60 and a voltage regulator 70 via the transistor Q 3 .
  • the voltage source V CC will produce a large enough control bias on the resistor R 14 of the voltage divider unit 94 to drive the field effect transistor Q 4 to be on.
  • the control bias is larger than the sum of the on voltage of the field effect transistor Q 4 and the reference voltage, the field effect transistor Q 4 immediately enters the on state to keep the transistor Q 3 on.
  • the electronic device 10 When the electronic device 10 is to stop providing power, it provides a low-level trigger signal S TR for end of power supply.
  • the low-level trigger signal S TR drives a transistor Q 7 in the second switch unit 40 to be off.
  • the microprocessor 50 immediately outputs a high-level signal to drive a transistor Q 6 in a third switch unit 80 to be on.
  • the gate G of the field effect transistor Q 4 is connected to the reference terminal Gnd to drive the field effect transistor Q 4 to be off.
  • the transistor Q 3 After the field effect transistor Q 4 is off, the transistor Q 3 immediately enters the off state, and the voltage source V CC stops providing power to the load 60 and the voltage regulator 70 .
  • the leakage current I DSS of the field effect transistor Q 4 will increase, and the base current I B3 flowing through the transistor Q 3 increases therewith. Because the collector current I C is ⁇ times the base current I B according to the transistor's characteristics, the collector current I C3 of the transistor Q 3 will increase with the base current I B3 . The increase of the collector current I C3 of the transistor Q 3 will cause an increase in the voltage of the gate G of the field effect transistor Q 4 .
  • the voltage of the gate G has to be larger than the sum of the pinch-off voltage V T of the field effect transistor Q 4 and the voltage drop across the at least two series-connected diodes D 11 and D 12 .
  • the increase of the leakage current I DSS will lead the base current I B3 and the collector current I C3 of the transistor Q 3 to rise in succession.
  • the voltage of the gate of the field effect transistor Q 4 generated when the collector current I C3 flowing through the third resistor R 14 is still smaller than the sum of the pinch-off voltage V T of the field effect transistor Q 4 and the voltage drop across the at least two series-connected diodes D 11 and D 12 , the field effect transistor Q 4 won't cause erroneous actions even if there is any variation in temperature. Therefore, the power supply switch circuit can work stably without any influence from transistor's leakage current in high-temperature environments.
  • the present invention makes use of a PNP transistor and an N-channel field effect transistor to achieve current leakage protection so that the circuit won't produce erroneous actions due to the increase of leakage current in high-temperature environments.

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.

Description

    BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The present invention relates to a power supply switch circuit with current leakage protection and, more particularly, to a circuit used in an electronic device and capable of preventing the erroneous actions caused by a circuit leakage current in high temperature environments.
  • 2. Description of Related Art
  • As shown in FIG. 1, a prior art power supply switch circuit is primarily formed by connecting two transistors Q1, Q2 and other electronic components. When power is to be supplied, a trigger signal ST is used to control the transistor Q1 to be on so that a voltage source VCC can provide power to a load 90 via the transistor Q1. Meanwhile, the supplied power can also be sent to the base of the transistor Q2 to make the transistor Q2 on. After the transistor Q2 is on, the base of the transistor Q1 will be connected to a reference terminal Gnd to keep the transistor Q1 on. When the power is to be cut off, a controller 91 will send a cut-off signal to the transistor Q2 to make the transistor Q2 off. The transistor Q1 will then be off in succession so that the voltage source VCC can no longer provide power to the load 90.
  • The leakage current of a transistor depends on the working temperature. The magnitude of the leakage current is proportional to temperature. Please refer to FIG. 1 again. According to the transistor's characteristics, when the circuit stops providing power, the transistor Q2 will have a leakage current ICEO. When the temperature rises, the leakage current ICEO increases, and the base current IB1 flowing through the transistor Q1 increases therewith. Because the collector current IC is β times the base current IB according to the transistor's characteristics, the collector current IC1 of the transistor Q1 will increase with the base current IB1 of the transistor Q1. Similarly, the base current IB2 of the transistor Q2 increases with the collector current IC1 of the transistor Q1. With the increase of the base current IB2 of the transistor Q2, the leakage current ICEO increases. In this vicious circle, the power supply switch circuit will generate erroneous actions. That is, when the power supply switch circuit is originally in the off state (i.e., stops providing power), the transistor Q1 will be on due to the leakage current ICEO to drive the power supply switch circuit into the on state (i.e., starts providing power).
    • SUMMARY OF THE INVENTION
  • An object of the present invention is to provide a power supply switch circuit with current leakage protection, which is used in an electronic device and capable of preventing the erroneous actions caused by a circuit leakage current in high temperature environments.
  • The present invention comprises a transistor, a field effect transistor and a third resistor. The transistor has an emitter, a base and a collector. The emitter is connected to a voltage source. The collector is connected to a load via a forward biased diode. The field effect transistor has a drain, a source and a gate. The drain receives a trigger signal. The source is connected to a reference terminal via at least two series-connected diodes. The gate is connected to the collector via a second resistor. One terminal of the third resistor is connected to the gate, and the other terminal is connected to the reference terminal.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:
  • FIG. 1 is a circuit diagram of a prior art power supply switch circuit;
  • FIG. 2 is a circuit diagram of a power supply switch circuit with current leakage protection of the present invention; and
  • FIG. 3 is a circuit diagram showing how the present invention is used in an electronic device.
    • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • FIG. 2 is a circuit diagram of a power supply switch circuit with current leakage protection of the present invention. The power supply switch circuit with current leakage protection is used in an electronic device (not shown), and can prevent the erroneous actions caused by a leakage current in high temperature environments. The power supply switch circuit with current leakage protection comprises a transistor Q3, a field effect transistor Q4 and a third resistor R14. The transistor Q3 has an emitter E, a base B and a collector C. The emitter E is connected to a voltage source VCC. The collector C is connected to a load 92 via a forward biased diode D13. The field effect transistor Q4 has a drain D, a source S and a gate G. The drain D is connected to the base B of the transistor Q3 via a first resistor R12, and receives a trigger signal ST1. The source S is connected to a reference terminal Gnd via a voltage clamp unit 93. The voltage clamp unit 93 provides a reference voltage, and is formed by series connecting at least two diodes (D11, D12) together in this embodiment. The gate is connected to the collector C of the transistor Q3 via a second resistor R13. One terminal of the third resistor R14 is connected to the gate G of the field effect transistor Q4, and the other terminal is connected to the reference terminal Gnd.
  • The second resistor R13 and the third resistor R14 are series connected together to form a voltage divider unit 94. The power supply switch circuit with current leakage protection of the present invention further comprises a capacitor C11 and a fourth resistor R11, which are parallel connected between the emitter E and the base B of the transistor Q3. The transistor Q3 is a PNP transistor, and the field effect transistor Q4 is an N-channel field effect transistor.
  • Please refer to FIG. 2 again. When the power supply switch circuit supplies power normally, it receives a low-level trigger signal ST1 for the activation of power supply. The low-level trigger signal ST1 drives the transistor Q3 to be on. After the transistor Q3 is on, the voltage source VCC provides power to the load 92 via the transistor Q3. Because the transistor Q3 is on, the voltage source VCC will produce a large enough control bias on the resistor R14 of the voltage divider unit 94 to drive the field effect transistor Q4 to be on. When the control bias is larger than the sum of the on voltage of the field effect transistor Q4 and the reference voltage, the field effect transistor Q4 immediately enters the on state. After the field effect transistor Q4 is on, the base B of the transistor Q3 is connected to the reference terminal Gnd to keep the transistor Q3 on, thereby continuing providing power to the load 92.
  • When the circuit stops providing power, the field effect transistor Q4 will generates a leakage current IDSS. When the temperature rises, the leakage current IDSS increases, and the base current IB3 flowing through the transistor Q3 increases therewith. Because the collector current IC is β times the base current IB according to the transistor's characteristics, the collector current IC3 of the transistor Q3 will increase with the base current IB3. The increase of the collector current IC3 of the transistor Q3 will cause an increase in the voltage of the gate G of the field effect transistor Q4. However, because the source S of the field effect transistor Q4 is series connected to the voltage clamp unit 93 (i.e., at least two series-connected diodes D11 and D12), for the field effect transistor Q4 to be on, the voltage of the gate G has to be larger than the sum of the pinch-off voltage VT of the field effect transistor Q4 and the voltage drop across the at least two series-connected diodes D11 and D12.
  • When the present invention works in high-temperature environments, the increase of the leakage current IDSS will lead the base current IB3 and the collector current IC3 of the transistor Q3 to rise in succession. However, because the voltage of the gate of the field effect transistor Q4 generated when the collector current IC3 flowing through the third resistor R14 is still smaller than the sum of the pinch-off voltage VT of the field effect transistor Q4 and the voltage drop across the at least two series-connected diodes D11 and D12, the field effect transistor Q4 won't cause erroneous actions even if there is any variation in temperature. Therefore, the power supply switch circuit can work stably without any influence from transistor's leakage current in high-temperature environments.
  • FIG. 3 is a circuit diagram showing how the present invention is used in an electronic device. An electronic device 10 provides a high-level trigger signal STR for the activation of power supply. The high-level trigger signal STR is connected to a power supply switch circuit 20 via a first switch unit 30, and is connected to a microprocessor 50 via a second switch unit 40. The high-level trigger signal STR drives a transistor Q5 in the first switch unit 30 to be on. After the transistor Q5 is on, the base of the transistor Q3 is connected to the reference terminal Gnd so that the transistor Q3 is on. The voltage source VCC thus provides power to a load 60 and a voltage regulator 70 via the transistor Q3. Because the transistor Q3 is on, the voltage source VCC will produce a large enough control bias on the resistor R14 of the voltage divider unit 94 to drive the field effect transistor Q4 to be on. When the control bias is larger than the sum of the on voltage of the field effect transistor Q4 and the reference voltage, the field effect transistor Q4 immediately enters the on state to keep the transistor Q3 on.
  • When the electronic device 10 is to stop providing power, it provides a low-level trigger signal STR for end of power supply. The low-level trigger signal STR drives a transistor Q7 in the second switch unit 40 to be off. After the transistor Q7 is off, the microprocessor 50 immediately outputs a high-level signal to drive a transistor Q6 in a third switch unit 80 to be on. After the transistor Q6 is on, the gate G of the field effect transistor Q4 is connected to the reference terminal Gnd to drive the field effect transistor Q4 to be off. After the field effect transistor Q4 is off, the transistor Q3 immediately enters the off state, and the voltage source VCC stops providing power to the load 60 and the voltage regulator 70.
  • When the electronic device 10 stops providing power, if the temperature rises, the leakage current IDSS of the field effect transistor Q4 will increase, and the base current IB3 flowing through the transistor Q3 increases therewith. Because the collector current IC is β times the base current IB according to the transistor's characteristics, the collector current IC3 of the transistor Q3 will increase with the base current IB3. The increase of the collector current IC3 of the transistor Q3 will cause an increase in the voltage of the gate G of the field effect transistor Q4. However, because the source S of the field effect transistor Q4 is series connected to the at least two series-connected diodes D11 and D12, for the field effect transistor Q4 to be on, the voltage of the gate G has to be larger than the sum of the pinch-off voltage VT of the field effect transistor Q4 and the voltage drop across the at least two series-connected diodes D11 and D12.
  • When the present invention works in high-temperature environments, the increase of the leakage current IDSS will lead the base current IB3 and the collector current IC3 of the transistor Q3 to rise in succession. However, because the voltage of the gate of the field effect transistor Q4 generated when the collector current IC3 flowing through the third resistor R14 is still smaller than the sum of the pinch-off voltage VT of the field effect transistor Q4 and the voltage drop across the at least two series-connected diodes D11 and D12, the field effect transistor Q4 won't cause erroneous actions even if there is any variation in temperature. Therefore, the power supply switch circuit can work stably without any influence from transistor's leakage current in high-temperature environments.
  • To sum up, the present invention makes use of a PNP transistor and an N-channel field effect transistor to achieve current leakage protection so that the circuit won't produce erroneous actions due to the increase of leakage current in high-temperature environments.
  • Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.

Claims (14)

1. A power supply switch circuit with current leakage protection, said power supply switch circuit being used in an electronic device and capable of preventing the erroneous actions caused by a leakage current in high-temperature environments, said power supply switch circuit comprising:
a transistor having an emitter, a base and a collector, said emitter being connected to a voltage source, said collector being connected to a load, said base receiving a trigger signal;
a field effect transistor having a drain, a source and a gate, said drain being connected to said base via a first resistor, said gate being connected to said collector via a second resistor and a reference terminal via a third resistor; and
at least two series-connected diodes connected between said source and said reference terminal.
2. The power supply switch circuit with current leakage protection as claimed in claim 1, wherein said second resistor and said third resistor are series connected together to form a voltage divider unit.
3. The power supply switch circuit with current leakage protection as claimed in claim 1 further comprising a capacitor, wherein said capacitor is parallel connected between said emitter and said base of said transistor.
4. The power supply switch circuit with current leakage protection as claimed in claim 1 further comprising a fourth resistor, wherein said fourth resistor is parallel connected between said emitter and said base of said transistor.
5. The power supply switch circuit with current leakage protection as claimed in claim 1, wherein said transistor is a PNP transistor.
6. The power supply switch circuit with current leakage protection as claimed in claim 1, wherein said field effect transistor is an N-channel field effect transistor.
7. A power supply switch circuit with current leakage protection, said power supply switch circuit being used in an electronic device and capable of preventing the erroneous actions caused by a leakage current in high-temperature environments, said power supply switch circuit comprising:
a transistor whose conduction is controlled by a trigger signal;
a voltage divider unit connected to said transistor and used to output a control bias according to a conduction current of said transistor;
a field effect transistor connected to said transistor and said voltage divider unit, conduction of said field effect transistor being controlled by said control bias and used to keep said transistor on; and
a voltage clamp unit connected to said field effect transistor and providing a reference voltage to increase the level of an on voltage of said field effect transistor;
whereby conduction of said field effect transistor depends on whether said control bias is larger than the sum of said on voltage of said field effect transistor and said reference voltage.
8. The power supply switch circuit with current leakage protection as claimed in claim 7, wherein said transistor is a PNP transistor.
9. The power supply switch circuit with current leakage protection as claimed in claim 7, wherein said field effect transistor is an N-channel field effect transistor.
10. The power supply switch circuit with current leakage protection as claimed in claim 7, wherein said field effect transistor is connected to said transistor via a first resistor.
11. The power supply switch circuit with current leakage protection as claimed in claim 7, wherein said voltage divider unit comprises a second resistor and a third resistor, and those are connected in series.
12. The power supply switch circuit with current leakage protection as claimed in claim 7 further comprising a capacitor, wherein said capacitor is parallel connected between an emitter and a base of said transistor.
13. The power supply switch circuit with current leakage protection as claimed in claim 7 further comprising a fourth resistor, wherein said fourth resistor is parallel connected between an emitter and a base of said transistor.
14. The power supply switch circuit with current leakage protection as claimed in claim 7, wherein said voltage clamp unit comprises at least two diodes, and said diodes are connected in series.
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DE202005019801U1 (en) 2006-03-16
US7474085B2 (en) 2009-01-06
US20080186007A1 (en) 2008-08-07
FR2889894B3 (en) 2007-07-06
CA2532860A1 (en) 2007-02-16
FR2889894A3 (en) 2007-02-23
TWM285800U (en) 2006-01-11

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