Introduction to Optical Switch Driving Circuit and Its Principle

Function of the circuit

Optical switches are widely used in automatic production lines in factories as sensors for detecting the presence of obstructing objects. Almost all such products are assembled with small components, and their outputs are relay contact type or open collector type. This circuit is a simple and stable optical switch driving circuit.

How the Circuit Works

In order to make the LED have a large peak current flow, a pulse current with a small proportion is used to make the LED emit light. The circuit uses NE555IC, and R2 is selected with a relatively low resistance value, which can generate a pulse of RW=0.7C1.R2. The same period is determined by R1, which is generally about 1MS.

The characteristic of this circuit is that when TR2 is turned off, C2 is charged through R5, and when TR2 is turned on, C2 is discharged, so that LED1 obtains a large current. Even if TR2 is damaged and causes a short circuit, the LED can be protected. In addition, because of the pulse light emission method, the power consumption can be reduced.