Power supply control device for protecting a load and method of controlling the same

• US 6,222,355 B1
• Filed: 12/28/1999
• Issued: 04/24/2001
• Est. Priority Date: 12/28/1998
• Status: Expired due to Term

• Current Assignee: Yazaki Corporation
• Original Assignee: Yazaki Corporation
• Inventors: Watanabe, Mitsugu, Ohshima, Shouzou
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/472,871
• Time in Patent Office: 483 Days
• Field of Search: 323/282, 323/284, 323/273, 323/274, 323/313, 323/289
• US Class Current: 323/282
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 2017/0806 against excessive temperature

Abstract

When the power supply from a power source 101 to a load 102 is controlled in a switching manner by a semiconductor switch QA, reference voltage generating means (QB, Rr) generates a reference voltage (VDSB) having a voltage characteristic substantially equivalent to that of a voltage between the terminals of the semiconductor switch QA being connected to a predetermined load. Detecting means CMP1 detects a difference between the voltage (VDSA) between the terminals of the semiconductor switch QA and the reference voltage (VDSB). Control means which consists of the gate driver 111 amd CMP1 performs an on/off control of the semiconductor switch QA in accordance with the difference between the voltage (VDSA) between the terminals of the semiconductor switch and the reference voltage (VDSB).

Claims

1. A power supply control device comprising:

a semiconductor switch responding to a control signal applied to a control signal input terminal thereof to be switched and controlling the supply of electric power from a power supply to a load;

a reference voltage generator, connected in parallel to said semiconductor switch and operative to generate a reference voltage having a voltage characteristic substantially equivalent to that of a voltage between terminals of said semiconductor switch;

a detector operative to detect a difference between the voltage of the terminals of said semiconductor switch and said reference voltage; and

a controller operative to perform an on/off control of said semiconductor switch in accordance with said difference between the voltage of the terminals of said semiconductor switch and said reference voltage,

wherein when the voltage across the terminals of said semiconductor switch is lower than the reference voltage, said controller performs the on/off control of said semiconductor switch, and when said controller continues performing the on/off control for a predetermined time or a predetermined number of times, the semiconductor switch is turned off.

2. A power supply control device in accordance with claim 1, wherein said reference voltage generator includes a circuit connected in parallel with said semiconductor switch and said load, said circuit contains a series circuit including a second semiconductor switch and a second load, and generates a voltage between the terminals of said second semiconductor switch as said reference voltage.

3. A power supply control device in accordance with claim 1, wherein a voltage characteristic of the reference voltage of said reference voltage generator is substantially equivalent to a voltage characteristic in a state where a target current, which is in excess of a maximum current within a normal operation range, flows into said semiconductor switch and said load.

4. A power supply control device in accordance with claim 2, wherein a transient voltage characteristic of a voltage between the terminals of said semiconductor switch when said semiconductor switch shifts its state from an off state to an on state is equivalent to the corresponding one when said second semiconductor switch shift its state from an off state to an on state.

5. A power supply control device in accordance with claim 2, wherein a current capacity of said second semiconductor switch is smaller than that of said semiconductor switch, and a resistance ratio of said load and said second load is substantially inversely proportional to a current capacity ratio of said semiconductor switch and said second semiconductor switch.

6. A power supply control device in accordance with claim 1, further comprising:

a second reference voltage generator operative to generate a second reference voltage having a voltage characteristic substantially equivalent to a voltage characteristic of the voltage between the terminals of said semiconductor switch, said second reference voltage being a voltage between the terminals of a third semiconductor switch, said second reference voltage generator including a circuit, connected in parallel with said semiconductor switch and said load, containing a series circuit composed of said third semiconductor switch switched in accordance with said control signal and a third load; and

a second detector operative to detect a difference between said voltage between the terminals of said semiconductor switch and said second reference voltage.

7. A power supply control device in accordance with claim 6, wherein a voltage characteristic of the reference voltage of said second reference voltage generator is substantially equivalent to a voltage characteristic in a state that a target current, which is below a minimum current within a normal operation range, flows into said semiconductor switch and said load.

8. A power supply control device in accordance with claim 6, wherein a transient voltage characteristic of a voltage between the terminals of said semiconductor switch when said semiconductor switch shifts its state from an off state to an on state is equivalent to the corresponding one when said third semiconductor switch shift its state from an off state to an on state.

9. A power supply control device in accordance with claim 6, wherein a current capacity of said third semiconductor switch is smaller than that of said semiconductor switch, and a resistance ratio of said load and said third load is substantially inversely proportional to a current capacity ratio of said semiconductor switch and said third semiconductor switch.

10. A power supply control device in accordance with claim 2, wherein one of said second and third loads includes a plurality of resistors and a resistance value of one of said second and third loads is adjustable by selectively connecting said plurality of resistors.

11. A power supply control device in accordance with claim 2, wherein one of said second and third loads includes variable resistors connected in parallel and a resistance value of one of said second and third loads is adjustable by said variable resistors.

12. A power supply control device in accordance with claim 2, further comprising:

a voltage divider operative to divide a voltage between the terminals of said semiconductor switch at a voltage division ratio based on a resistance value ratio, and for applying the resultant voltage to said detector, and said voltage division ratio of said voltage divider is adjusted through a resistance value variation.

13. A power supply control device in accordance with claim 1, wherein said controller performs an off control of said semiconductor switch when a difference between the detected terminal-to-terminal voltage and said reference voltage exceeds a first threshold value, and an on control of said semiconductor switch when a difference between the detected terminal-to-terminal voltage and said reference voltage is below said second threshold value.

14. A power supply control device in accordance with claim 1, further comprising:

an overheat protector operative to protect said semiconductor switch by performing an off-control of said semiconductor switch when said semiconductor switch is excessively heated over a predetermined value.

15. A power supply control device in accordance with claim 14, wherein said semiconductor switch, said reference voltage generator, said detector, said controller, said second reference voltage generator, said second detector and said overheat protector are fabricated on a single chip.

16. A power supply control device in accordance with claim 15, wherein said second load within said reference voltage generator and said third load within said second reference voltage generator are mounted outside said chip.

17. A power supply control device in accordance with claim 1, wherein a period of the on/off control of said semiconductor switch by said controller is used as a control clock signal.

18. A power supply control device in accordance with claim 1, further comprising:

an inhibitor operative to inhibit said controller from performing the on/off control by said semiconductor switch during a fixed time period after said semiconductor switch is turned on.

19. A power supply control device in accordance with claim 14, further comprising:

an overheat cut-off accelerator operative to accelerate the off control by said overheat protector when said controller performs the on/off control of said semiconductor switch.

20. A power supply control device in accordance with claim 1, further comprising:

a timer control which operates such that said timer control accumulates the number of on/off controls of said semiconductor switch by said controller, and when the number of on/off controls reaches a predetermined number of times, said timer control performs an off control of said semiconductor switch.

21. A method of controlling a power supply control device having a first semiconductor switch which responds to a control signal applied to a control signal input terminal to be switched and controls the supply of electric power from a power supply to a load, said method comprising the steps of:

generating a reference voltage from a second semiconductor switch which has a voltage characteristic substantially equivalent to that of a voltage between the terminals of said first semiconductor switch;

detecting a difference between the voltage between the terminals of said first semiconductor switch and said reference voltage;

performing an on/off control of said first semiconductor switch in accordance with said difference between the voltage between the terminals of said first semiconductor switch and said reference voltage.

22. A method of the power supply control device in accordance with claim 21, wherein in said reference voltage generating step, a voltage characteristic of the reference voltage is substantially equivalent to a voltage characteristic in a state that a target current, which is in excess of a maximum current within a normal operation range, flows into said first semiconductor switch and said load.

23. A method of the power supply control device in accordance with claim 21, wherein the act of controlling includes:

performing an off control of said first semiconductor switch when a difference between the detected terminal-to-terminal voltage and said reference voltage exceeds a first threshold value; and

performing an on control of said first semiconductor switch when a difference between the detected terminal-to-terminal voltage and said reference voltage is below said second threshold value.

24. A method of the power supply control device in accordance with claim 21, further comprising:

protecting said first semiconductor switch by performing an off-control of said first semiconductor switch when said first semiconductor switch is excessively heated.

25. A method of the power supply control device in accordance with claim 21, further comprising:

an inhibiting step for inhibiting a controller from performing the on/off control by said first semiconductor switch during a fixed time period after said first semiconductor switch is turned on.

26. A method of the power supply control device in accordance with claim 24, further comprising:

accelerating the off control of said first semiconductor switch when the semiconductor switch on/off control is performed.

27. A method of the power supply control device in accordance with claim 21, further comprising:

accumulating the number of on/off controls of said first semiconductor switch by a controller, and when the number of on/off controls reaches a predetermined number of times, said time control step performs an off control of said semiconductor switch.