JPS609860Y2 - Noise isolation circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a noise isolation circuit.

In recent years, logic circuits such as microcomputers have come into widespread use, and most of their power supply voltage is +5V DC, and such logic circuits drive relays RL to automatically control air-conditioning equipment, etc. In this case, the operating voltage of the relay RL is, for example, +12V or +24V, which is at least higher than +5V of the logic circuit and cannot be shared with the voltage of the logic circuit. A circuit was used in which the emitter of the transistor Tr1 on the logic circuit side and the emitter of the transistor Tr2 in the relay power supply circuit were connected to the ground side in common.

However, the operating voltage range of relay RL is generally larger than that of logic circuits, and +5V for normal logic circuits is stabilized by a constant voltage circuit, etc., and +24V for relays is not stabilized, so the ACI QQV side of this circuit is When noise is mixed into the power supply, the stabilized +5V noise is reduced by the power supply circuit, but the +24V noise passes through as is.

Therefore, noise from +24V flows to +5V side,
This causes voltage fluctuations in the ground line, which adversely affects the operation of logic circuits using +5V as a power source, causing malfunctions.

In order to prevent the influence of such noise, as shown in Figure 2,
A method has been considered to reduce the amount of noise by inserting a resistor R3 between the emitters of the transistor Tr□ on the logic circuit side and the transistor Tr2 on the relay RL side, but in this method, the DC noise amplified by the transistor Tr1 as well as the AC bone noise Therefore, there is a limit to the value of the resistor R3.

In consideration of these points, the present invention inserts an inductance into the common ground side of two circuits with different power supplies, thereby blocking noise from one circuit and preventing any adverse effects on the other circuit. It is an object of the present invention to provide a noise cutoff circuit which is capable of cutting off noise and has no effect on the output signal amount of the other circuit.

Next, an embodiment of the present invention will be described with reference to FIG.

1 is a logic circuit such as a microcomputer, and this logic circuit 1 is a circuit whose power supply is a stabilized +5V DC power supply, and a resistor R1 and a transistor Tr are provided at its output end, and from this transistor Tr1, a resistor R1 and a transistor Tr are provided. The output signal drives relay RL.

This relay RL is connected to a relay circuit 2 whose power source is an unstable +24V AC power source different from that of the logic circuit 1 due to the necessity of its operating voltage.

Further, this relay circuit 2 is provided with a transistor Tr2 whose collector is connected to the relay RL, and the base of this transistor Tr2 is connected to the collector of the transistor Tr□ of the logic circuit via a resistor R2.

Further, the emitters of the transistor Tr□ of the logic circuit 1 and the transistor Tr2 of the relay circuit 2 are connected to a common ground line, and an inductance L is inserted between the two emitters.

In such a configuration, transistor Tr1 amplifies the output signal from logic circuit 1 and transmits it to transistor Tr2 via resistor R2, and relay RL is driven by transistor Tr2.

The relay (RL) is configured to automatically control, for example, an air conditioning system (not shown).

Furthermore, the emitter of the transistor Tr1 and the transistor T
Because the inductance L inserted between the emitter of r2 separates the stabilized +5V of logic circuit 1 and the unstable +24V of relay circuit 2 in AC terms, high frequency components are generated in the unstable +24V. When noise from sources such as
Those noise pulses with fast falling inductance L
The noise is absorbed or rounded by the AC noise, and only the AC noise is blocked and the DC noise is not affected.

As a result, the stabilized +5V is not affected by noise, and the signal amount of the logic circuit 1, which is a DC component, is not reduced, so that the logic circuit 1 operates normally.

According to the present invention, the common earth side parts of two circuits with different power supplies are connected via an inductance, so if noise gets into one circuit, this noise will not flow to the other circuit. can be absorbed by the inductance, noise can be blocked without reducing the amount of output signal from the other circuit, and malfunction of the circuit due to the influence of noise can be prevented.

For example, when adding a relay circuit to a logic circuit,
Noise from an unstable relay circuit can be reliably blocked from a stabilized logic circuit, and the normal operation of the logic circuit is not hindered.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a circuit before the improvements of the present invention, Fig. 2 is a circuit diagram showing an example of a conventional noise cut-off circuit, and Fig. 3 is an implementation of the noise cut-off circuit of the present invention. FIG. 3 is a circuit diagram showing an example. 1...Logic circuit as a circuit, 2...
Circuit for relay as a circuit, L...Inductance.

Claims (1)

[Scope of utility model registration request] A noise isolation circuit characterized in that a common ground side part of two circuits using different power supplies is connected via an inductance.