JPS62138020A - Source change-over circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for limiting the in-dash current generated when a relay is turned on in a circuit that uses a relay to turn on and off a DC power supply.

2. Description of the Related Art Conventionally, in text multiplex receivers and the like, a remote control signal is used to control a relay to switch the power supply on and off. However, when switching the relay from the disconnected state to the on state, a large in-dash current is generated in the power line, causing a reduction in the reliability of the relay.

Therefore, as a countermeasure, a resistor or coil is inserted in series in the power supply line to limit the in-dash current.

First, such a conventional in-dash current limiting circuit will be explained.

In Fig. 3, 1 is a transistor for stabilizing the 5V power supply, 2 is a Zener diode for stabilizing the base voltage of transistor 1, 3 is a diode for correcting its temperature characteristics,
4 is a DC relay, 5 is a resistor that determines the Zener current of Zener diode 2, 6.7 is a resistor for limiting the in-dash current that occurs when relay 4 is turned on, and 8 is controlled by a remote control signal to turn on relay 4. This is a switching transistor for relay switching that is turned on when the relay is switched on. Load circuit engineers who are supplied with a +5V power supply require a stable power supply voltage (within ±0.1V) at low voltage and large current (+5V).

The load circuit (2), which is supplied with a +12V power supply, is a high voltage, small current (→~12V, 0.15A) circuit that does not require much stability in the power supply voltage.

In such a circuit, when the base voltage of transistor 8 is set to a high level (+5V) by the remote control signal 2, transistor 8 becomes conductive, current flows through the excitation coil of relay 4, and its contacts SW1 and SW2 become conductive. Therefore, +6v and +1 are applied to the load circuits ■ and ■.
2V power is supplied. On the load side, since large-capacity smoothing capacitors are connected between the power supply line and the ground, the contacts SW1. SW2 becomes conductive and a large in-dash current (transient current) flows at the next moment.

To prevent this, in-dash current limiting resistors 6 and 7 are inserted in series in each power supply line.

Problems to be Solved by the Invention However, in the conventional configuration as described above, when the load current of the load circuit f connected to the +67 line increases, the voltage drop across the resistor 6 increases, and the +5V line with respect to the load current increases. The voltage fluctuation characteristics of the resistor 6 deteriorate, and when the load current increases to 1 A or more, the resistor 6 alone cannot limit the in-dash current.

In view of the above-mentioned problems, an object of the present invention is to provide a circuit that has good voltage fluctuation characteristics with respect to current fluctuation (r) in a load circuit that requires a large current, and can reduce in-dash current when a relay is turned on. That is.

Means for Solving the Problems In order to solve the above problems, the power supply switching circuit of the present invention stabilizes the voltage on the input side of the large current side by using the output on the /J current side switched by a relay. This is designed to start up the switching circuit and provide delay characteristics to the rise of the output voltage on the large current side.

OPERATIONS According to the present invention, with the above-described configuration, the voltage characteristics are not affected by current fluctuations in a load circuit with a large current value, and moreover, it is possible to effectively limit the magnitude of the in-dash current generated when the relay is turned on.

Embodiment Below, a power supply switching circuit according to an embodiment of the present invention will be described.
This will be explained with reference to the drawings.

In FIG. 1, parts similar to those in FIG. 2 are designated by the same reference numerals, and explanations thereof will be omitted.

In this circuit, voltage is applied to the base of transistor 1 from one end of a smoothing capacitor connected between the +12V power supply line for small current load circuit ■ and the ground on the output side of contact SW2 of relay 4. There are characteristics.

In this configuration, when a high level (+5V) signal is applied to the base remote control of transistor 8 at To, transistor 8 becomes conductive, current flows through the excitation coil of relay 4, and contacts SW1. SW2 is turned on.

When the contact becomes conductive, charging of the capacitor 9 begins, and the base voltage of the transistor 10 for stabilizing the +sV line begins to rise. Its base voltage is 0 at T1.
When the voltage exceeds 8V, the emitter voltage of the trunk 21 also rises, and the voltage of the power supply line from the contact SW1 to the load circuit 2 rises. A delay (time lag) of Δt occurs until the emitter voltage rises. For this reason, when the contact SW1 becomes conductive at TO, current is not yet supplied from the transistor 1, and thereafter the current gradually increases, so that almost no in-dash current is generated at the contact SW1.

At this time, electrolytic capacitor 9 between +12v line and ground
absorbs the in-dash current flowing to the +12V line when contact SW2 becomes conductive at TO, prevents the in-dash current from flowing into the base of transistor 1 from the +12V line, and delays the base voltage of transistor 1. And it is intended to be started up gradually.

As described above, according to this embodiment, after the relay 4 is turned on, the voltage of the +5V line on the large current load circuit I side is gradually raised with a slight delay. As a result, there is no need to insert a resistor to prevent in-dash current in series, so the voltage is not influenced by changes in the load current, and the in-dash current can be effectively limited without deteriorating the power supply stabilization characteristics. I can do it.

Effects of the Invention As described above, according to the present invention, in a circuit in which one relay switches the power supply to a large current load circuit I and a small current load circuit By gradually starting up the voltage stabilizing transistor on the large current load circuit I side with a delay, the power supply stabilization characteristics are not deteriorated even by changes in the large current load current. 0, which can effectively limit the in-dash current.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a power switching circuit according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the voltage rise when the relay becomes conductive, and Fig. 3 is a conventional power switching circuit. 01.8...transistor, 2...zener diode, 3...
・Diode, 4...Relay, 5゜6.7...
...Resistance, 9... Electrolytic capacitor. Name of agent: Patent attorney Toshio Nakao and one other person:

Claims (1)

[Claims] A relay is provided that has contacts that switch between supplying power to load circuit I, through which a large current flows, and power supply to load circuit II, through which a small current flows, respectively, from the output side of the contact for load circuit II to the power supply for load circuit I. A power supply switching circuit configured to apply a voltage to a voltage stabilizing transistor connected in series with the contact of the transistor to gradually start up the transistor with a delay from the turning on of the contact.