Load driving circuit capable of raised accuracy detection of disconnection and short circuit of the load

• US 20030021073A1
• Filed: 07/29/2002
• Published: 01/30/2003
• Est. Priority Date: 07/27/2001
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Nagata, Junichi
• Granted Patent: US 6,804,096 B2
• Time in Patent Office: Days
• US Class Current: 361/78
• CPC Class Codes: H03K 17/063 in field-effect transistor switches
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches

Abstract

A load driving circuit controls a feed of a power supply voltage of a power supply to a load. A power MOSFET is connected in series with the power supply and the load. A load driving state such as disconnection and short circuit of the load is detected by comparing a predetermined reference voltage and a voltage of the load and MOSFET node. For this, a pull-up resistor is connected between the power supply and the load. A diode is connected between source and gate of the MOSFET. A transistor circuit is connected between source and gate of the MOSFET to discharge a gate capacitance of the MOSFET. In a non-feed mode, a driving current is made to flow in a control electrode of the transistor circuit. The magnitude of the driving current is preferably enough to operate the transistor circuit and the voltage drop caused by the driving current is preferably smaller than a difference between the power supply voltage and the predetermined reference voltage.

Claims

1. A circuit for controlling a feed of a power supply voltage of a power supply to a load wherein the circuit has a function of detecting a load driving state, the circuit comprising:

a MOSFET connected in series with said power supply and said load for effecting an on/off operation;

means responsive to a feed control signal given from external for supplying a driving voltage to said gate to turn said MOSFET on;

a resistor connected between said power supply and said load for causing a voltage drop during an off period of said MOSFET;

detection means for providing a signal indicative of said load driving state on the basis of a comparison between a predetermined reference voltage and a voltage of a node between said load and said MOSFET;

protection means connected between a source and a gate of said MOSFET for providing a protection against a reverse bias applied between said source and gate by bypassing;

transistor means connected between said source and gate of said MOSFET for discharging a gate capacitance of said MOSFET; and

driving means responsive to a non-feed indication by said feed control signal for flowing a driving current in a control electrode of said transistor means such that a magnitude of said driving current is enough to operate said transistor means and said voltage drop caused by said driving current is smaller than a difference between said power supply voltage and said predetermined reference voltage.

2. A circuit as defined in claim 1, wherein said transistor means includes a plurality of transistors in such a configuration that a channel current of one of said transistors flows in a control electrode of a next transistor.

3. A circuit as defined in claim 1, wherein said driving means comprises:

resistor means for providing such a resistance as let said driving current flow; and

means, serially connected to said resistor means and responsive to said feed control signal, for effecting an on/off operation.

4. A circuit as defined in claim 1, wherein said driving means comprises:

current source means for providing said driving current; and

means, responsive to said non-feed indication, for enabling said current source means to operate.

5. A circuit as defined in claim 1, wherein said MOSFET is connect between said power supply and said load and said MOSFET is of an N-channel type and wherein said transistor means includes a PNP transistor.

6. A circuit as defined in claim 1, wherein said MOSFET is inserted in a low side of said load and said MOSFET is of a P-channel type and wherein said transistor means includes an NPN transistor.

7. An integrated circuit for use in a load driving circuit for controlling a feed of a power supply voltage of a power supply to a load wherein the load driving circuit has a function of detecting a load driving state, the integrated circuit comprising:

upstream and downstream pins to which said power supply and said load are to be connected such that a power supply current by said power supply flows from said upstream pin to said downstream pin;

a MOSFET to be connected in series with said power supply and said load for effecting an on/off operation;

means responsive to a feed control signal given from external for supplying a driving voltage to said gate to turn said MOSFET on;

upstream and downstream pins for enabling said serial connection of said MOSFET, said power supply and said load wherein an external resistor is connected between said upstream and downstream pins to cause a voltage drop during an off period of said MOSFET;

detection means for providing a signal indicative of said load driving state on the basis of a comparison between a predetermined reference voltage and a voltage of a node between said load and said MOSFET;

protection means connected between a source and a gate of said MOSFET for providing a protection against a reverse bias applied between said source and gate by bypassing;

transistor means connected between said source and gate of said MOSFET for discharging a gate capacitance of said MOSFET; and

means responsive to a non-feed indication by said feed control signal for flowing a current in a control electrode of said transistor means such that a magnitude of said current is enough to operate said transistor means and said voltage drop caused by said current is smaller than a difference between said power supply voltage and said predetermined reference voltage.