Many Electronic circuit projects in simple ways of learning

Mini Phototransistor light switch controller circuit

You may like a Mini Phototransistor light switch controller circuit. We use photo transistor to be a light sensor and Schmitt Trigger CMOS Digital IC. The output drives current out off a load or an external circuit can power up to 25mA.

Mini Phototransistor light switch controller circuit


Mini Phototransistor light switch controller circuit

This circuit uses one photo transistor, one Schmitter triggers IC and a few components only. It can help you in many ways, it is up to you.

  • To drive a small load directly, with load current maximum 25mA
  • To take a relay (in a 12V coil) without a transistor driver.
    It saves time and money for you.
  • To apply the component like Optocoupler type.
    To drive the faster switching load, AC or DC, and high-voltage.

The circuit working

See in circuit. First, a normal light comes to the photo-transistor-Q1. The current flows through the junction of its collector-emitter, and potentiometer-VR1 to ground.

Second, there is a voltage drop across VR1, to be “high” status. To trigger the input of the first Schmitt Trigger IC1/6, the output(pin 12) makes “low” status.


Third, we connect the 5 others Schmitt trigger in parallel.
They become to the inverter gate.

According to the input is “low”.
Thus, the output voltage is “high”.
It is special that can drive the output current maximum of about 25 mA.
Normal CMOS is 5mA only.

The resistor-R1 and capacitor-C1 in the RC network will block the noise. Which it may come in the circuit. If you have too many The problem of noise may increase slightly the C1,

The variable resistor-VR1, to adjust the sensitivity of the phototransistor switching. When the light comes on.

The circuit can supply up to 16 volts.

Keep reading: ‘Automatic led night light switch’ »

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu