Intro: Variable Bench Power Supply With Active Cooling
I needed a new bench power supply that would be variable and inexpensive. I decided to reuse an old laptop power adapter that was not being used anymore and it gave me a nice filtered 19 volts DC. I then made up the circuit for the LM350 Variable voltage regulator on a breadboard to make sure it worked. The circuit for the LM350 is really simple, uses few components and is readily available online. After doing some testing I realized that when you draw more than 1.5 amps of current the LM350 runs hot, it is rated for 3 amps with a large Heat Sink. To help the Heat Sink I decided to have a small 12 volt 2" fan automatically come on when it detects significant heat on the heat sink. To Do this I used the LM311 automatic fan control that uses a thermistor to sense temperature, the circuit for this is also readily available online and its really simple to make. To power this circuit, the fan and the voltmeter I used a LM7812 which is a really simple 12 volt regulator. I would have liked to used a Trim pot with a knob on the front but I did not already have one that was the right value. Other than that everything worked out great and I was able to reuse things that I already had.