Relay drive circuit

Abstract

A potential of an end of the coil is inputted to a plate-OFF detecting portion which detects OFF-tendency in which a plate of a relay is about to get apart from a head of a core of the relay. When the OFF-tendency is detected, a coil current for supplying a coil of the relay is set to a first current value with which a plate of an electromagnetic relay is drawn and a movable contact of the relay comes in contact with a fixed contact of the relay. When an external disturbance ends, the coil current is returned to a second current value, which is smaller than the first current value, so that the movable contact and the fixed contact are kept in contact with each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objective, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a circuit structure of a relay drive circuit according to a first embodiment of the present invention;

FIG. 2A is a side view of a detailed structure of an electromagnetic relay in an OFF state;

FIG. 2B is a side view of the detailed structure of the electromagnetic relay in an ON state;

FIG. 3 is a schematic diagram showing a circuit structure of a plate-OFF sensing portion of the relay drive circuit shown in FIG. 1;

FIG. 4 is a timing chart showing an example of the operation of the relay drive circuit;

FIG. 5 is a timing chart in a case where a sudden external disturbance occurs;

FIG. 6A is a timing chart in a case where an Ir required value does not change while an electric current Ir is being reduced from its maximum to a holding current;

FIG. 6B is a timing chart in a case where the Ir required value changes while the electric current Ir is being reduced from its maximum to the holding current;

FIG. 7 is a schematic top view of an electric connection box;

FIG. 8 is a cross sectional view of the electric connection box taken along the line VII-VII in FIG. 7;

FIG. 9 is a schematic circuit diagram showing a relay drive circuit according to a fourth embodiment of the present invention;

FIG. 10 is a schematic diagram showing a circuit structure of a plate-OFF sensing portion of the relay drive circuit shown in FIG. 9; and

FIG. 11 is a schematic circuit diagram showing a relay drive circuit according to a fifth embodiment of the present invention.

Claims

1. A relay drive circuit for controlling, based on ON/OFF operation of a relay switch, power supply to a coil of an electromagnetic relay in order to control power supply to a load, the relay including the coil; a core inserted in the coil; a plate including magnetic material, the plate magnetically drawn to come in contact with a head of the core when the coil is supplied with electric power, the plate getting apart from the head when the coil is not supplied with electric power; a movable contact moving along with the plate; and a fixed contact installed to the coil, the relay drive circuit comprising: a first drive portion for setting a coil current to be supplied to the coil to a first current value with which the plate is drawn to the head of the coil and the movable contact comes in contact with the fixed contact;a second drive portion for setting the coil current to a second current value which is smaller than the first current value set by the first drive portion, so that the movable contact and the fixed contact are kept in contact with each other;a current switching portion for switching between supplying the coil with the coil current having the first current value set by the first drive portion and supplying the coil with the coil current having the second current value set by the second drive portion; anda plate-OFF detecting portion for detecting, based on change of a potential at an end of the coil, OFF-tendency in which the plate is about to get apart from the head of the coil,wherein the current switching portion switches to supplying the coil with the coil current having the first current value set by the first drive portion, when the plate-OFF detecting portion detects the OFF-tendency.

2. The relay drive circuit according to claim 1 wherein, the current switching portion is located at a low-side of the relay and drives the relay through the low-side, andthe plate-OFF detecting portion detects the OFF-tendency based on change of a potential at the low-side of the coil.

3. The relay drive circuit according to claim 2 wherein, the plate-OFF detecting portion includes a highpass filter for passing only high frequency components in the potential at the low-side of the coil, andthe plate-OFF detecting portion detects the OFF-tendency when change of the high frequency components is larger than a threshold.

4. The relay drive circuit according to claim 1 wherein, the current switching portion is located at a high-side of the relay and drives the relay through the high-side, andthe plate-OFF detecting portion detects the OFF-tendency based on change of a potential at the high-side of the coil.

5. The relay drive circuit according to claim 1, further comprising: an optimum current setting portion for controlling the current switching portion so that the second current value becomes optimal,wherein the optimum current setting portion sets, when the plate-OFF detecting portion detects the OFF-tendency while the coil current with the second current value is being supplied to the coil, a new value as the second current value which is larger than an old value set as the second current value before detection the OFF-tendency.

6. The relay drive circuit according to claim 5, wherein, the current switching portion switches, when the relay switch is turned to ON, to supplying the coil with the coil current having the first current value so as to draw the plate so that the movable contact comes in contact with the fixed contact,the current switching portion subsequently switches to supplying the coil with the coil current having the second current value,the optimum current setting portion subsequently decreases the second current value gradually from an initial current value, andthe optimum current setting portion sets, on detecting the OFF-tendency in decreasing the second current value, the new value as the second current value which is larger than an old value which was the second current value at the time of the detection the OFF-tendency.

7. The relay drive circuit according to claim 5, wherein, the current switching portion switches, when the plate-OFF detecting portion detects the OFF-tendency, to supplying the coil with the coil current having the first current value so as to draw the plate so that the movable contact comes in contact with the fixed contact,the current switching portion subsequently switches to supplying the coil with the coil current having the second current value,the optimum current setting portion subsequently decreases the second current value gradually from an initial current value, andthe optimum current setting portion sets, on detecting the OFF-tendency in decreasing the second current value, the new value as the second current value which is larger than the old value set as the second current value before the detection the OFF-tendency.

8. The relay drive circuit according to claim 5, wherein, the optimum current setting portion includes: a D/A converter for generating a potential corresponding to a counter value; andan optimum current control portion for counting the counter value, andthe relay drive circuit changes the potential outputted by the D/A converter by changing the counter value of the optimum current control portion so as to decrease the current value of the coil current gradually from the first current value.

9. The relay drive circuit according to claim 5, wherein, the optimum current setting portion includes an optimum current control portion including a counter for counting a counter value,the current switching portion includes a constant current D/A converter for executing weighting based on the counter value so as to change a value of a current to output from the constant current D/A converter, andthe relay drive circuit changes the value of the current outputted by the constant current D/A converter by changing the counter value of the optimum current control portion so as to decrease the current value of the coil current gradually from the first current value.

10. An electric connection box for installing the relay drive circuit according to claim 1 and the relay cited in claim 1, comprising: a wiring member to be electrically connected with the relay drive circuit and the relay;a case in which the relay drive circuit and the relay is installed as well as the wiring member; andan external connector terminal connected with the wiring member, the external connector terminal extended to an outside of the case.