JPS5811077Y2 - switching circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to improvements in switching circuits.

For example, as shown in Figure 1, two car stereos A
, B share a set of speakers L, SP, R, SP, a switching circuit designated by symbol C has conventionally been used as a switching circuit for switching the speakers.

In this circuit, when relay Y is de-energized, its contact y
1, y2 are in the state shown by the solid line in the figure, so if you connect the speakers L, SP, R, and SP to car stereo B, and turn on switch SW2 of car stereo B in this state, the car stereo B The output of is the speaker,
Played on SP, R-3P, but on another car stereo A
When the switch SW1 is turned on, the contacts y1 and y2 are switched to the dashed line side, and the output of the car stereo A is automatically reproduced through the speakers L, SP, R, and SP.

Switching of the contacts yl and y2 at this time is performed as follows.

That is, when the switch SW1 of the car stereo A is turned on, the current flowing there flows through the diode D1. The current is shunted through the emitter and base of the transistor Q and resistors R1 and R2, which turns on the transistor Q, and the collector current energizes the relay Y, which connects the contacts y 1 ,
y2 switches.

However, in this conventional example, if the power supply +V is a battery, and the voltage includes a ripple component, when the input voltage to the switching circuit C drops due to the ripple, the car stereo The input terminal of A cannot rapidly follow the ripple voltage because the internal power supply filter capacitor C8 has a charge stored therein, so the diode D1 becomes reverse biased and turns off, and at the same time the transistor Q is also turned off, and as a result, contacts y 1 and y 2 of relay Y repeatedly turn on and off in accordance with the ripple frequency, leading to an extremely abnormal condition.

In addition, even when switch SW2 is turned on and car stereo A is inactive and the other car stereo B is operating, the capacitor Co of car stereo A is rapidly charged via diode D1 at the peak of ripple. , at the time of ripple tipping, the charge of the cositizer C6 is discharged via the resistors R1 and R2.

Therefore, the transistor Q turns on at the charging current at the peak of the next ripple, returns to off when charging is completed, and similarly turns on and off depending on the ripple frequency.
It repeatedly turns off, leading to abnormal conditions.

As described above, in the conventional circuit configuration, whenever the switch of any car stereo is turned on, a switching malfunction occurs due to the ripple component of the power supply, resulting in an extremely inconvenient situation.

In addition, if the ignition key of the car is turned off while car stereo A is not working,
A voltage higher than the withstand voltage is applied to the base and emitter of the transistor Q by the capacitor C8, and the transistor Q
There was also a risk that it would be destroyed.

Therefore, an object of the present invention is to provide a switching circuit that solves the above-mentioned problems by adding some circuit elements.

Hereinafter, one embodiment will be described with reference to FIG. 2. In this figure, the resistor R2 of the switching circuit C in FIG. 1 is replaced with a diode D2, and a capacitor C1 is inserted between the base and collector of the transistor Q. This is what I did.

In this state, when switch SW1 of car stereo A is turned on, current flows to it through diode D1. The current flows in a shunt manner to the emitter and base of the transistor Q and the diode D2, so that the transistor Q is turned on (however,
For example, it is assumed that a silicon diode is used as the diode D1, a germanium diode is used as the diode D2, and a germanium transistor is used as the transistor Q, and the ON condition of the transistor Q is satisfied.

Due to the on state of the transistor Q, the capacitor C1 connected between the base and the collector is almost in a discharge state.

Here, if the input voltage drops due to ripples in the power supply, the input terminal of car stereo A will be able to quickly follow the ripple voltage because charge is stored in the internal power filter capacitor C8. First, diode D1 becomes reverse biased and turns off, but at this time transistor Q
are not turned off simultaneously due to the charging current of capacitor C1, and a base current sufficient to excite relay Y is provided for a certain time constant.

In addition, when switch SW2 of car stereo B is turned on and contacts yl and y2 are returned to the solid line side,
Transistor Q is in an off state, and if a ripple component appears in the power supply at this time, diode D1. Due to the presence of D2, there is no discharge path in the power supply circuit of the car stereo A, and the peak value of the power supply is merely held in the capacitor C6, and the transistor Q is not turned on.

Furthermore, even when the ignition key is turned off,
Diode D1. Transistor Q is protected by D2 and there is no risk of destruction.

As described above, according to the present invention, there is no adverse effect due to the ripple component of the power supply, and there is no effect even when the power supply is instantaneously shut off by an ignition switch or the like.

[Brief explanation of the drawing]

FIG. 1 is a switching circuit diagram of a car stereo including a conventional switching circuit, and FIG. 2 is a switching circuit diagram of the present embodiment.

Claims (1)

[Scope of utility model registration request] In a switching circuit including a switch driving transistor whose base current is part of the current to be passed through a device connected to an output terminal, a capacitor is connected between the base and collector of the transistor, and a capacitor is connected between the base and the device. A switching circuit characterized in that a forward diode is connected to the .