First scratch built bench power supply

I suppose sooner or later a beginning electronics hobbyist builds his own bench power supply. Probably like a rite of passage. So I’ve finished mine, and my first project completely designed and built from scratch instead of kits.

I got some help on these forums, which helped me learn how to handle thermal resistance calculations and how to connect a shunt for an ammeter with a common ground.

So here are some photos and specs:

Input: 120VAC 60 Hz

Outputs:
Fixed voltages: 24, 18, 12, 9 and 5, at up to 700mA
Variable voltage 1.3 to 30 Volts up to 2 Amps

Features:
LED meters for variable voltage output, and for current drawn from any voltage supply
Coarse and Fine voltage adjust
Microprocessor controlled fan speed with over-temp warning, temp sensor failure warning, and POST.

I had originally planned to control the fan with a simple Schmitt trigger using a 555 timer. But in the mean time I learned to program microprocessors, so this is also my first operational project using a PIC.

It’s all stuffed in a Serpac project box that is entirely too small. The three circuit boards are 1) linear regulators & heat sinks, 2) rectifier, filter cap and bleeder, and 3) PWM Fan control and adjustable shunt on the return.

Cheers,

-- Dan

Hi Dan,
Its outside looks very nice. Its inside is too crowded (as you know)

If it is set for 3.3V at 2A then the poor variable regulator must dissipate about 70W and it will cook itself and everything inside. The tiny fan will spin like crazy.

But if the variable regulator is an LM350K then it will reduce its output current to as low as only 250mA to protect itself.

Did you use a separate regulator for each of the fixed voltages?

Yea it's just a chain of 5 linear regulators. The 12V also feeds the fan, the 5V also feeds the meters and microprocessor. The LM350 is in the TO-3 package.

-- Dan