JPH05260678A - Protective circuit for electric device on vehicle - Google Patents

Abstract

PURPOSE:To provide a means for solving the breakdown strength deterioration of the inner components of a generator and protecting the electric device connected to the generator when the generator goes wrong. CONSTITUTION:A surge voltage absorbing means 12 for absorbing surge voltage is provided to suppress the inner voltage of a generator. It can be accomplished without installing another component by using this surge voltage absorbing means 12 in combination with the rectifier of the generator. Moreover, a mechanism 104 is provided, which checks the operation state of the surge voltage absorbing means 12 and stops the operation of the generator when surge absorption is not performed completely. A group of rectifiers yield at the fixed voltage of 100V or thereabout, and does not generate voltage above this. Therefore, it becomes possible to design the inner components in the same shapes as before.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for an on-vehicle electric device, and more particularly to protection of a generator driven by an internal combustion engine of an automobile or the like and an electric device supplied with power by the generator. In particular, the present invention relates to ensuring safety accompanying the increase in power supply voltage, which has been attracting attention in recent years.

[0002]

2. Description of the Related Art A technique relating to an on-vehicle electric device is disclosed in JP-A-1
Attempts have been made to improve distribution efficiency by using multi-system voltage including high voltage as seen in Japanese Patent Publication No. 157236. However, there is no discussion of protection for higher voltage generators. On the other hand, as a power supply device for automobiles,
As described in US Pat. No. 3,571,657, the rectifier of the generator is replaced with a Zener diode to suppress accidental surge generation (eg battery load dump surge that occurs when the battery and electric load are released simultaneously). The method is discussed. However, there is no example of a technology that combines both.

[0003]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In the present invention, there are problems in the near future that are required to increase the voltage of a generator. (1) A method for solving deterioration in withstand voltage of internal parts of the generator (2) Generator The solution to the method of protecting the electrical equipment connected to the generator in the event of a fault is described.

[0004]

With respect to the above-mentioned problems, (1) can be achieved by providing surge voltage absorbing means for absorbing surge voltage so as to suppress the internal voltage of the generator. In particular, by sharing this surge voltage absorbing means with the rectifier group of the generator, this can be achieved without installing a separate component.

The item (2) can be achieved by checking the operating state of the surge voltage absorbing means described in (1) and providing a mechanism for stopping the operation of the generator when the surge absorption is not completely performed. ..

[0006]

The above rectifier group has a constant voltage (100V or more because the conventional generator is designed to withstand a voltage of 100V or more in consideration of battery load, dump, surge).
The following is appropriate. Further, if it is too large, it does not play a role of protection, and it is suitable that it is about 4 times or less of the regulation voltage. ), And no more voltage is generated. Therefore, the internal parts can be designed with the same shape as the conventional one (in particular, the insulation distance between terminals to which a high voltage is applied). Also, by monitoring the output voltage, the breakdown voltage is set to a preset value (100 in the above example).
When it is higher than V), power generation is stopped by interrupting the field current flowing in the field winding of the generator to protect electric devices connected inside and outside the generator.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of an electric device of an automobile, which is assumed to have a voltage system of 48V. In FIG. 1, reference numeral 1 is a generator, and a voltage regulator 1
0, three-phase armature winding 11, three-phase full-wave rectifier 12 composed of six Zener diodes, and field winding 13. A battery 2 is charged from the output terminal of the generator. An electric device 3 is supplied with electric power from the generator 1 through the switch 4. Further, the voltage regulator 10 includes a power transistor 101, a diode 102, an AND gate 103, a voltage regulator circuit 104, an overvoltage detection circuit 105.
It is composed of

In this configuration, the voltage adjusting circuit 1 is normally operated.
05 preferentially operates, and the current flowing through the field winding 13 is adjusted according to the voltage of the battery 2. Here, an example of the internal circuit of the voltage adjusting circuit 105 is shown in FIG. 2 in FIG.
Reference numerals 51 and 1052 are resistors, and 1053 is a capacitor. Reference numeral 1054 is a comparator, and 1055 is a sawtooth wave generator. The battery voltage input to the terminal a is divided by the resistors 1051 and 1052 and smoothed by the capacitor 1053. Then, the comparator 1054 compares it with the sawtooth wave and outputs a rectangular wave having a constant frequency. This rectangular wave has a high duty when the voltage of the terminal a is low, and has a low duty when the voltage of the terminal a is high.

Returning to FIG. 1, normally, the terminal d is "1".
If it is (high level), the power transistor 101 is turned on / off according to the duty signal of the terminal b, the average current flowing through the field winding 13 increases when the voltage of the battery 2 is low, and the battery 2 When the voltage is high, the average current flowing through the field winding 13 decreases. When the current flowing through the field winding 13 increases, the output voltage of the generator 1 increases, so that negative feedback is applied and the voltage of the battery 2 is controlled to a constant value.

Here, the electric device 3 is turned on as needed, but assuming that a large current is flowing through the electric device 3 and the switch 4 is suddenly cut off, the electric current of the field winding 13 is Overvoltage occurs because the voltage cannot be rapidly reduced.
This overvoltage is absorbed when the battery 2 is connected, but cannot be absorbed when the battery 2 is disconnected for some reason or when the battery fluid is exhausted.
This phenomenon is called battery load dump surge,
100V with a 12V generator, 150 with a 24V generator
An overvoltage of about 200V is observed with a V, 48V generator.

Therefore, in the 48V system, a higher voltage may be applied than in the conventional 12V system. However,
The three-phase full-wave rectifier 12 has a Zener characteristic, and suppresses generation of a high voltage due to breakdown against such a surge. The generally well-known characteristics of the Zener diode are as shown in FIG. 4, which causes breakdown at the reverse voltage Vz. In FIG. 1, for example, the armature windings 11a, 11a are momentarily
If b is emitting a high voltage (the armature winding 11a is on the high voltage side), the zener diode 12d breaks down, and a voltage of Vz + Vf is generated as the output voltage of the generator. Here, Vf is Zener diode 12a-1
The forward voltage drop of 2f is about 1V. Vz is 1
Assuming 00V, Vz + Vf = 101V, and 12V
It can be suppressed to the same surge voltage as the system.

Next, FIG. 3 shows an internal circuit of the overvoltage detection circuit. Reference numerals 1041 and 1042 are resistors, 1043 is a reference voltage source, and 1044 is a comparator. 1045,104
Reference numeral 6 is a NAND gate forming a flip-flop, and 1047 is a power-on reset circuit.

The power-on reset circuit 1047 is used when a voltage is applied to the terminal c (that is, the battery 2 is the generator 1).
A reset signal. When the reset signal is issued, the output of the NAND gate 1046 becomes "1" and the output of the AND gate 103 of FIG.
Follow Next, assume that the breakdown voltage of the Zener diode becomes high for some reason or the surge voltage cannot be absorbed. When an abnormal voltage is generated in this way, the voltage at the inverting input terminal (−) of the comparator 1044 is the reference voltage source 10
It becomes higher than the voltage of 43 and the output of the comparator 1044 is "0".
become. Then, the output of the NAND gate 1045 becomes "1" and this value is held. At this time, the inputs of the NAND gate 1046 are all "1" and the output d is "0". Then, the output of the AND gate 103 in FIG. 1 becomes "0", the power transistor 101 is cut off, the field current does not flow, and the generator 1 stops the power generation. Therefore, the occurrence of overvoltage is also eliminated. According to the present embodiment, the occurrence of overvoltage can be suppressed by the Zener diode 12, and the power generation can be stopped even when the Zener diode is damaged, so that the safety of the electric system of the automobile can be improved. .. As a method of detecting overvoltage, the overvoltage detection terminal c may be connected to one end of the armature winding as shown in FIG. Further, not only the single voltage system as described above, but also the system having different voltage systems can obtain the same effect.

[0014]

According to the present invention, it is possible to enhance the safety of the electric system of an automobile which employs a high voltage system.
Further, since it is possible to suppress the surge voltage to the same level as that of the conventional (12V system), it is not necessary to particularly consider the insulating property of the internal parts of the generator, so that the size of the generator can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electric device including an on-vehicle generator according to an embodiment of the present invention.

FIG. 2 is an internal circuit diagram of a voltage control circuit 105 in FIG.

3 is an internal circuit diagram of an overvoltage detection circuit 104 in FIG.

FIG. 4 is a characteristic diagram illustrating a single characteristic of the rectifier 12 in FIG.

FIG. 5 is a circuit diagram of an in-vehicle electric device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Generator, 2 ... Battery, 10 ... Voltage regulator, 12 ...
Three-phase full-wave rectifier, 13 ... Field winding, 104 ... Overvoltage detection circuit, 105 ... Voltage control circuit.

Claims (3)

[Claims] 1. An armature winding, a rectifier group for converting an AC output of the armature winding into a direct current, a field winding supplying a magnetic flux to the armature winding, and a current control of the field winding. In a vehicle-mounted power supply system including a generator having a voltage regulator that adjusts the DC output of the rectifier group to a constant value, and an electric device group connected to an output terminal of the generator, the rectifier group is 100 V or less. A protection circuit for an in-vehicle electric device, which has a breakdown voltage. 2. An armature winding, a rectifier group for converting an AC output of the armature winding into a direct current, a field winding supplying a magnetic flux to the armature winding, and a current control of the field winding. Then, in a vehicle-mounted power supply system comprising a generator having a voltage regulator for adjusting the DC output of the rectifier group to a constant value, and an electric device group connected to the output terminal of the generator, the rectifier group is the voltage A protection circuit for an in-vehicle electric device, which has a breakdown voltage of 150% to 400% of a regulation voltage of a regulator. 3. An armature winding, a rectifier group for converting AC output of the armature winding into DC, a field winding for supplying magnetic flux to the armature winding, and a current control of the field winding. Then, in a vehicle-mounted power supply system comprising a generator having a voltage regulator for adjusting the DC output of the rectifier group to a constant value, and an electric device group connected to the output terminal of the generator, the output voltage of the generator And a breaker circuit for shutting off the output of the voltage regulator when the voltage exceeds the breakdown voltage of the rectifier group.