JPH1070839A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the capacity of a main switch in a power supply circuit as small as possible. SOLUTION: A power capacitor C1 which is parallel to a load 1 is connected with a main switch SW1 connected with a battery BT via the contact of a precharge relay RY1, and the contact point of a fail safe relay RY2 is arranged in parallel to a precharge resistor R1. A control system power supply 2 in which a power supply voltage signal is inputted by the operation of the relay RY1, a reset circuit 3 which outputs a delay operation signal of a specified time, and a CPU 4 wherein reset is canceled by the reset circuit 3 are installed. When the switch is turned on, the relay RY2 is excited by the CPU 4 in the state that the relay RY1 is excited, charge is performed via a resistor, and the switch can be prevented. When the switch is turned off, the relay RY2 is put in the state of nonexcitation prior to the relay RY1 in the state of excitation, discharge is performed via the resistor, and welding of the relay contact can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for charging and discharging a power capacitor connected between a power supply and a load and in parallel with the load by turning on / off a switch.

[0002]

2. Description of the Related Art In a power drive unit for a DC motor or an AC motor, for example, when a main power supply such as a battery or a stabilized power supply is turned on, a rush current to a power capacitor built in the unit may be a problem.

As a countermeasure against the above-mentioned problem, a power relay or a switch having a high current capacity is provided so that a problem such as welding does not occur even if the rush current occurs. For example, FIG. As shown, a load 11 is connected to the positive side of a battery BT as a power supply via a switch SW2, and a power capacitor C1 branched from a node between the switch SW2 and the load 11 and connected in parallel with the load 11.
There is a circuit provided with. However, in the circuit of FIG. 3 described above, when the switch SW2 is a mere on / off switch, the power capacitor C1 at the time of the off is used.
There is a problem that there is no discharge path.

In another circuit example shown in FIG. 4, a changeover switch SW3 is connected between the positive side of the battery BT and the load 11.
, A precharge resistor R6 is provided between the changeover switch SW3 and the load 11, and a power capacitor C1 is provided in parallel with the load 11. Further, a contact of a fail-safe relay RY3 is provided between the positive side of the battery BT and the load 11, bypassing the changeover switch SW3 and the precharge resistor R6. Its fail safe relay RY
No. 3 coil with the changeover switch SW3 and the precharge resistor R
6, and the coil is energized / de-energized by a transistor Tr3 which operates in response to an on / off signal input from the outside.

In the circuit of FIG. 4 configured as described above, the precharge resistor R6 for precharging the power capacitor C1 is switched by the relay RY3, so that charging and discharging can be performed while suppressing the rush current. ing. However, in this case, the changeover switch SW3 as the main switch requires a combination switch having a certain withstand current capacity.

[0006]

Therefore, in a power drive unit such as a motor, a main switch for turning on the power is a single-type small signal for on / off, and a relay is provided inside the unit so as to allow a motor current. There is a demand to control on / off the coil current of the relay. In this case, the above-described conventional circuit configurations cannot cope with the problem, and if only the main relay is used, the inrush current of the power capacitor causes a problem that the relay contacts are welded.

[0007]

SUMMARY OF THE INVENTION In order to solve such a problem and to minimize the capacity of a main switch in a power supply circuit, in the present invention, a power supply is provided between a power supply and a load. A power supply circuit configured to charge / discharge a power capacitor connected in parallel to the load by turning on / off a provided switch, wherein the power supply is excited by turning on the switch to connect the power supply to the power capacitor. A first relay, a precharge resistor provided between a contact of the first relay and the power capacitor, a second relay having a contact connected in parallel to the precharge resistor, A delay means for outputting a delay operation signal after a lapse of a predetermined time from the operation of the first relay; and a second means for receiving the delay operation signal in cooperation with the first relay in an energized state. During excites the relay and the switch-off was assumed and a relay control means for the second relay earlier than the first relay in the non-excited state.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to specific examples shown in the accompanying drawings.

FIG. 1 is a diagram showing a power supply circuit to which the present invention is applied. As shown in the figure, a single-type ON / OFF small signal type main switch SW1 is connected to the positive side of a battery BT as a power supply, and a node between the battery BT and the main switch SW1 is connected to a first node. Normally open terminal S of the contact of the precharge relay RY1 as a relay
1a is connected. The normally closed terminal S1b of the contact of the precharge relay RY1 is grounded, and the common terminal S1c is connected to the load 1 via the precharge resistor R1. The load 1 is, for example, a pre-driver or a power element circuit of a circuit that drives and controls a DC or AC motor. A power capacitor C1 provided in parallel with the load 1 is connected to a node between the precharge resistor R1 and the load 1.

When the main switch SW1 is turned on, the coil L1 of the precharge relay RY1 is excited through the diode D1 connected in the forward direction, and is connected to the node between the diode D1 and the coil L1. The connected capacitor C2 is charged. Also, the main switch SW1 and the diode D
A diode D2 and a pair of resistors R2 and R3 are connected in series, branching from the node 1 and the transistor Tr1 is turned on by the voltage divided by the resistors R2 and R3 when the main switch SW1 is turned on. It has become.

A common terminal S1c of the contact of the precharge relay RY1 is connected to a normally open terminal S2a of a contact of a fail-safe relay RY2 as a second relay, and a coil L2 of the fail-safe relay RY2.
Is also connected. A transistor Tr2 is provided between the coil L2 and the transistor Tr1, so that the power supply voltage is applied to the coil L2 via the contact of the precharge relay RY1 which is switched to the normally open terminal S1a in the excited state. Therefore, when both transistors Tr1 and Tr2 are turned on, the coil L2 is excited.

The coil L of the precharge relay RY1
A diode D3 is connected to both ends of the diode 1 so that current flows from the ground side to the power supply side. Similarly, diodes D4 are connected to both ends of the coil L2 of the fail-safe relay RY2 so that current flows from the ground to the power supply.

A node between the common terminal S1c of the contact of the precharge relay RY1 and the precharge resistor R1 is connected to the control system power supply 2. The control system power supply 2
The reset of the CPU 4 is released by an output signal of a reset circuit 3 as a delay unit that performs a delay operation by power supply from the CPU 4, and an ON signal is output from the CPU 4 to the transistor Tr2. Further, there is provided a relay control means for controlling the fail-safe relay RY2 by a circuit constituted by the control system power supply 2, the reset circuit 3, the CPU 4, and the transistors Tr1, Tr2.

Next, the operation of this power supply circuit will be described with reference to FIG.
It is shown below with reference to the time chart. First, when the main switch SW1 is turned on, the capacitor C2 is charged as described above, and after a lapse of time until its full charge, the coil L1 of the precharge relay RY1 is excited, and the contact of the capacitor C2 moves to the normally open terminal S1a side. , The charging of the power capacitor C1 is started.

When the precharge relay RY1 is switched to the normally open terminal S1a, the battery voltage BT is input to the control system power supply 2, so that a control system power supply voltage is generated. The generation of the control system power supply voltage causes the reset circuit 3
The power-on reset of the CPU 4 is performed via the CPU, but the timing is set to be delayed until the power capacitor C1 is fully charged. Then, an ON signal is output from the CPU 4 at the timing of the power-on reset, the transistor Tr2 is turned on, the coil L2 of the fail-safe relay RY2 is excited, and the contact is switched to the normally open terminal S2a.

After the fail-safe relay RY2 is excited, a current can flow to the load 1 through both contacts of the pre-charge relay RY1 and the fail-safe relay RY2, that is, bypassing the pre-charge resistor R1. Therefore, the rush current to the power capacitor C1 when the power is turned on to turn on the main switch SW1 is equal to the precharge resistance R1
, The welding of the contacts of the main switch SW1 due to the rush current can be prevented.

Next, when the main switch SW1 is turned off, the coil current flowing through the coil L1 of the precharge relay RY1 is maintained for a certain time by the diode D3, and the excitation state of the precharge relay RY1 is maintained. Further, since the voltage (V1) of the coil L1 when the precharge relay RY1 is off is considerably small, the resistance R2
If the voltage division (V2) by R3 is set to V2> V1, the transistor Tr1 is turned off before the precharge relay RY1 is turned off, the emitter of the transistor Tr2 is changed from the ground state to the floating state, and the precharge relay is set. The fail safe relay RY2 is turned off before RY1.

Thus, the fail-safe relay R
After turning off Y2, the precharge relay RY1 turns off, and the power capacitor C1 changes the precharge resistance R1 ·
It is discharged via the normally closed terminal S1b of the precharge relay RY1. Therefore, when the main switch SW1 is turned off, the discharge current of the power capacitor C1 flows through the contact of the precharge relay RY1 via the precharge resistor R1, so that the contact of the contact of the precharge relay RY1 can be prevented.

In order to further ensure the above operation, in this specific example, diodes D1 and D2 and a capacitor C2 are provided. This makes it possible to keep the ON time of the precharge relay RY1 long, to provide a sufficient margin for the mechanical operation delay of the relay, and to provide a fail-safe relay by turning off the main switch SW1. It can be ensured that the precharge relay RY1 is turned off from the off of RY2. Further, reverse connection protection of the power supply can be performed by the diodes D1 and D2.

[0020]

As described above, according to the present invention, when the switch is turned on, the second relay is excited with a delay, so that the power capacitor is first charged via the precharge resistor, and then the power capacitor is connected in parallel with the precharge resistor. The current can flow to the load through the contact of the second relay provided in the switch, and a large current due to the rush current to the power capacitor at the time of switch-on does not flow to the switch. Can be When the switch is turned off, the second relay is de-energized before the first relay, and the contact of the first relay is turned off in a state where the discharge current of the power capacitor flows through the pre-charge resistor. Therefore, welding of the relay contact can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a power supply circuit to which the present invention is applied.

FIG. 2 is a time chart showing the operation of the power supply circuit.

FIG. 3 is a diagram showing a power supply circuit using a conventional power capacitor.

FIG. 4 is a diagram showing a power supply circuit using a conventional precharge resistor.

[Explanation of symbols]

 Reference Signs List 1 load 2 control system power supply 3 reset circuit 4 CPU 11 load C1 power capacitor R1 precharge resistor RY1 precharge relay RY2 fail safe relay

Claims (1)

[Claims] 1. A power supply circuit for charging / discharging a power capacitor connected in parallel to a load by turning on / off a switch provided between a power supply and a load, wherein the switch turns on to excite the power capacitor. A first relay that is connected to connect the power supply and the power capacitor; a precharge resistor provided between a contact of the first relay and the power capacitor; and a parallel connection to the precharge resistor. A second relay having a set contact, a delay means for outputting a delayed operation signal after a lapse of a predetermined time from the operation of the first relay, and the delayed operation signal in cooperation with the first relay in an excited state. And a relay control means for energizing the second relay in response to the switch and turning off the second relay prior to the first relay when the switch is turned off. Power supply circuit, characterized and.