JP2002175124A - Power circuit for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reverse connection of a battery to a power circuit for vehicle and prevent surges, using a small, low-cost constitution without voltage drops. SOLUTION: A switching circuit 50 and a smoothing circuit 52 are connected via a reverse connection preventing circuit 10 and a surge protection circuit 30 to an input side plus terminal 1 connected to a battery. The reverse connection preventing circuit includes a relay switch 20 which is turned on upon receiving power supplied from the battery connected in the normal direction, and when the battery is connected in the reverse direction, the relay switch is turned off to prevent a reverse current from flowing to the switching circuit and the like. The surface protection circuit includes an FET 31 controlled by transistor 35 and 42, and when a Zener diode 37 is turned on by a surge, the FET is turned off to protect the switching circuit and the like. Since no diode is used for preventing the battery from being connected in the reverse direction, no voltage drop will occur, and the Zener diode for detecting surges can be a small one that is used merely for controlling the transistor 42.

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 electric equipment of a vehicle.

[0002]

2. Description of the Related Art A vehicle is equipped with a battery as a power source for its electric equipment and a power supply circuit for supplying a predetermined constant voltage to the electric equipment regardless of the state of the battery. In the vehicle power supply circuit, the input side is a DC battery, so the
There is a demand for measures to protect the internal circuit when the minus terminal is connected in reverse, and measures against surges due to the effects of the motor mounted on the vehicle and the like.

As such a power supply circuit, for example, there is one as shown in FIG. As input terminals, a plus terminal 1 to which a plus electrode of the battery is connected and a minus terminal 2 to which a minus electrode is connected are provided, and the minus terminal 2 is grounded (GND). A surge absorbing element 62 composed of a large Zener diode is connected between the plus terminal 1 and the minus terminal 2. When a surge voltage higher than a predetermined voltage is applied, the surge voltage is absorbed by the surge absorbing element 62.

The positive terminal 1 is further connected to a switching circuit 50 via a reverse connection preventing diode 64 having the positive terminal side as an anode. Then, a smoothing circuit 52 is connected to the switching circuit 50, and the smoothing circuit 52
Is connected to the output terminal 60. The reverse connection prevention diode 64 prevents a reverse current from flowing through the switching circuit 50 and the smoothing circuit 52 when the battery is connected to the input terminal with the electrodes reversed.

[0005] Series-connected resistors 55 and 56 are provided between the output of the smoothing circuit 52 and GND, and a connection point S between the resistors 55 and 56 is connected to the switching circuit 50. The switching circuit 50 switches the current from the battery to the smoothing circuit 52 by duty control based on the potential of the connection point S, and performs feedback control of the output voltage of the smoothing circuit 52 to a predetermined value. Thus, a constant voltage is always output to the output terminal 60.

[0006] Further, a 12V battery is mounted on a general vehicle such as a passenger car. For example, a truck or a vehicle mainly driven in a cold region is often mounted with a 24V battery in order to increase the power supply capacity. Also in this case, it is preferable that the electrical equipment itself uses the same specification equipment in common, so that a predetermined constant voltage is output regardless of whether the battery is 24 V or 12 V, that is, even when a battery with different specifications is mounted. You.

[0007]

However, since the conventional power supply circuit has the surge absorbing element 62 for absorbing a high-voltage surge, the power supply circuit is not only used for a 12V battery but also for a 24V battery. It requires large ones and is expensive. Also, since the diode 64 is used as a countermeasure against the reverse connection of the battery,
In particular, as described above, in a circuit shared by high and low voltages, the diode 64, which must be set in correspondence with high voltage, causes a remarkable voltage drop, and when a low-voltage battery is connected, the effect of the output voltage drop is large. However, there is a problem that the time during which a stable output can be secured becomes short. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low-cost, low-cost vehicle power supply circuit with a small voltage drop in view of the above conventional problems.

[0008]

According to the present invention, there is provided a power supply circuit including a constant voltage circuit which outputs a predetermined voltage by connecting to a battery mounted on a vehicle, and is connected to the battery. On the power supply line between the input terminal and the constant voltage circuit, a relay switch that receives power from a battery that is properly connected and turns on is provided. When the battery is reversely connected, the constant voltage circuit is shut off from the battery because the relay switch does not turn on. No voltage drop occurs in the relay switch that is turned on in the normal connection state.

Further, the invention according to claim 2 is configured such that the relay switch receives the output of the constant voltage circuit and maintains its ON state. While the constant voltage circuit is operating normally, the relay switch is turned on by the output, and power from the battery is supplied to the constant voltage circuit.

According to a third aspect of the invention, there is provided a control circuit further comprising a switching element provided on a power supply line between an input terminal and a constant voltage circuit, and outputting a control signal for turning off the switching element based on a predetermined surge voltage. did. When the switching element is turned off, the constant voltage circuit is cut off from the surge voltage.

Particularly, in the invention of claim 4, the switching element is an FET, the control circuit is connected to the FET, and a first transistor for turning on the FET in a normal ON state; A second transistor that is connected and turns off the first transistor based on a predetermined surge voltage. A zener diode or the like for detecting a predetermined surge voltage may have a small capacity capable of controlling a transistor.

[0012]

FIG. 1 is a block diagram showing an embodiment of the present invention.
It will be described based on. As input terminals, a plus terminal 1 and a minus terminal 2 are provided, and the minus terminal 2 is grounded. The reverse connection prevention circuit 10 and the surge prevention circuit 30 are sequentially connected to the plus terminal 1, and the switching circuit 50 and the smoothing circuit 52 are connected subsequently to the surge prevention circuit 30. The output of the smoothing circuit 52 is connected to the output terminal 60, and the connection point S of the series-connected resistors 55 and 56 provided between the output of the smoothing circuit 52 and GND is connected to the switching circuit 50. Switching circuit 50
And the smoothing circuit 52 form a constant voltage circuit.

The reverse connection prevention circuit 10 includes a relay switch 20 having one contact 21 connected to the plus terminal 1. The positive terminal 1 further includes a diode 12 having the positive terminal side as an anode, and a capacitor 13 connected in parallel.
And one end of the coil 23 of the relay switch 20 via the resistor 14. The one end of the coil 23 is also connected to the output side of the smoothing circuit 52 via the diode 15. The other end of the coil 23 is grounded. A diode 16 having an anode on the ground side is connected to the coil 23 of the relay switch 20 in parallel. The other contact 22 of the relay switch 20 is connected to the surge prevention circuit 30.

The surge prevention circuit 30 includes a reverse connection prevention circuit 10.
A FET (field effect transistor) 31 is provided as a switching element connected between the other contact 22 of the relay switch 20 and the switching circuit 50 in FIG.
The gate of the FET 31 is connected to the input side (the reverse connection prevention circuit 10 side) of the FET 31 via the resistor 32,
The resistor 33 is connected to the collector of the transistor 35. The transistor 35 has an emitter grounded and a resistor 36 connected between the emitter and the base.

On the other hand, a Zener diode 37 is connected in series with the cathode side of the diode 12 connected to the plus terminal 1.
The resistor 38 and the resistor 39 are sequentially connected, and the other end of the resistor 39 is grounded. The diode 12 side of the Zener diode 37 is connected to the base of the transistor 35 via the resistor 40. Here, the breakdown voltage of the zener diode 37 is set to 40V.

The connection point between the resistor 40 and the base of the transistor 35 is grounded via the transistor 42. The base of the transistor 42 is connected to a connection point between the resistors 38 and 39, and is also connected to a capacitor 44 having one end grounded. Switching circuit 50 and smoothing circuit 52
Are the same as those in the conventional example of FIG.

In the circuit configured as described above, in the reverse connection prevention circuit 10, for example, when the normal connection is performed in which the plus electrode of the 24V battery is connected to the plus terminal 1 and the minus electrode is connected to the minus terminal 2, first, the plus terminal 1 Flows through the coil 23 of the relay switch 20 via the diode 12 and the capacitor 13. Thereby, the contact 2
1 and 22 are closed, and the voltage from the battery is supplied to the switching circuit 50 and the smoothing circuit 52 via the surge prevention circuit 30.

With the lapse of time immediately after connection, the capacitor 1
3 is charged and the coil side voltage v1 of the capacitor 13 decreases as shown in FIG. 2, but the output v2 of the smoothing circuit 52 is supplied to the coil 23 via the diode 15, so that the relay switch 20 The ON state is maintained. In the figure, v3 indicates a voltage at a point P on the downstream side of the relay switch, and is the same as the battery voltage. On the other hand, when the battery is connected to the input terminal with its electrode reversed, the current is blocked by the diode 12, so that no current flows through the coil 23 and the relay switch 20 is turned off.
Since it is in the (OFF) state, the switching circuit 50 and the smoothing circuit 52 are cut off from the battery connected in reverse.
Note that the resistor 14 is for holding the potential difference between both ends of the capacitor 13, and the diode 16 absorbs the induced electromotive force when the coil 23 is turned off.

In the surge prevention circuit 30, the transistor 35 whose base is connected to the plus terminal 1 via the resistor 40 (and the diode 12) is normally ON.
The FET 31 is turned on when its gate receives a voltage determined by the resistors 32 and 33. On the other hand, when a voltage of 40 V or more is input to the input terminal, the zener diode 37 is turned on, the voltage determined by the resistors 38 and 39 is supplied to the base of the transistor 42, and the transistor 42 is turned on. As a result, the transistor 35 becomes OF
F and the FET 31 is also turned off. Thus, the switching circuit 50 and the smoothing circuit 52 are cut off from the upstream side of the FET 31 and protected from surge. Note that the capacitor 44 performs initial absorption of the surge to the transistor 42, and the resistor 36 is for adjusting the base voltage of the transistor 35. The above-described circuit including the transistors 35 and 42 that operate according to ON / OFF of the zener diode 37 constitutes the control circuit of the present invention.

This embodiment is constructed as described above, and is provided with a reverse connection prevention circuit including a relay switch 20 as a countermeasure against the reverse connection of the battery. When the reverse connection is made, the switching circuit 50 and the smoothing circuit 52 are cut off by the relay switch. In addition, a diode that causes a voltage drop on the power supply line from the input terminal (plus terminal) to the switching circuit and the smoothing circuit is not required, and the voltage of the battery can be effectively used as indicated by v3 in FIG.

As a countermeasure against surge, FE is provided on the power supply line.
T / ON / OF via a small zener diode
Since the FET on the power supply line is controlled by the F-controlled transistor to cut off the switching circuit and the smoothing circuit from the surge, an expensive and large surge absorbing element is not required.

[0022]

As described above, according to the present invention, in a power supply circuit including a constant voltage circuit, a power supply from a normally connected battery is turned on on a power supply line between an input terminal connected to the battery and the constant voltage circuit. When the battery is connected in reverse, the relay switch is turned off and the constant voltage circuit can be cut off from the battery.Also, since a diode that causes a voltage drop is not used unlike the conventional case, even when the battery voltage is low, A stable output can be ensured for a long time by effectively utilizing the voltage.

Further, by configuring the relay switch to receive the output of the constant voltage circuit and maintain its ON state, the driving circuit of the relay switch is simplified.

According to a third aspect of the present invention, a switching element is provided on a power supply line between the input terminal and the constant voltage circuit, and the switching element is turned off by a control circuit when a surge occurs. It is possible to protect the constant voltage circuit from surge voltage without the need for a circuit.

In particular, the switching element is an FET,
By providing the control circuit with a first transistor that turns on the FET in the normal on state and a second transistor that turns off the first transistor based on a predetermined surge voltage, the power supply line is normally turned on. In addition, a Zener diode or the like for detecting a surge voltage, which does not cause a voltage drop, has an advantage that a much smaller capacity capable of controlling a transistor is required as compared with a conventional large one.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a change in voltage according to the embodiment.

FIG. 3 is a diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Positive terminal 2 Minus terminal 10 Reverse connection prevention circuit 12, 15, 16 Diode 13, 44 Capacitor 14, 32, 33, 36, 38, 39, 40, 55, 5
6 Resistance 20 Relay switch 21, 22 Contact 23 Coil 30 Surge prevention circuit 31 FET (switching element) 35 Transistor (first transistor) 42 Transistor (second transistor) 37 Zener diode 50 Switching circuit 52 Smoothing circuit 60 Output terminal

Claims (4)

[Claims] 1. A power supply circuit including a constant voltage circuit connected to a battery mounted on a vehicle and outputting a predetermined voltage, comprising: a power supply line between an input terminal connected to the battery and the constant voltage circuit; A power supply circuit for a vehicle, comprising a relay switch that is turned on by receiving power from a selected battery. 2. The vehicle power supply circuit according to claim 1, wherein said relay switch receives an output of said constant voltage circuit and maintains its ON state. 3. A control circuit comprising: a switching element provided on a power supply line between the input terminal and the constant voltage circuit; and a control circuit for outputting a control signal for turning off the switching element based on a predetermined surge voltage. Item 1 or 2
A power supply circuit for a vehicle as described in the above. 4. The switching element is an FET,
The control circuit is connected to the FET and turns on the FET in a normal ON state. The control circuit is connected to the first transistor and turns off the first transistor based on the predetermined surge voltage. The vehicle power supply circuit according to claim 3, further comprising a second transistor.