How to control secondary circuit using TTL

ttl

I have a very newbie and possibly stupid question, but I have been searching many sites and just can't find an answer.

Imagine you have a circuit, some device (electro-motor) that is powered with for example 20V dc power supply. Then you have another TTL circuit.

I am able to programatically change the output on TTL circuit to 0 (0,8V) or 1 (5V), but what I need to do is control the second circuit, using this digital output, that means, for example if I send 1 to output, the 20V device is switched on, when I send 0, it's turned off.

What is a simplest way to achieve this?

Best Answer

This is a very classic case to use a transistor as a switch.

Example:
enter image description here
Simulate circuit

  • The 300 Ohm resistor would be your load
  • The 1k resistor limits the base current
  • The 50Hz source simulates your 5V TTL output

Note that there are some things to consider when dimensioning the circuit. The transistor must be chosen to satisfy the collector current requirements. There are some other considerations, but this answer is not about transistor circuits in detail. There a plenty of resources in the WWW. Search for "transistor as a switch" and "emitter follower".

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