Posts Tagged ‘micrel’

Adjustable voltage circuit

July 27, 2010 14 comments

Ok, so the components have arrived. No doubt I’ve forgotten something and will have to order some more.

I’m starting with building the variable voltage circuit.

Parts list:

  • Micrel MIC29152WT low drop out adjustable voltage regulator
  • TO-220 heat sink
  • small piece of strip board (also called vero board)
  • solid core wire
  • solder
  • 5kΩ potentiometer
  • 560Ω resistor
  • 10µF capacitor
  • 22µF capacitor

Tools required:

  • Soldering Iron
  • multimeter
  • 12v power supply


This schematic is taken straight from the voltage regulator data sheet. Vin is the 12v from the power supply, R1 is the potentiometer and R2 is the 560Ω resistor. The capacitor on the left is 10µF and the capacitor on the right is 22µF.

I calculated the resistor values using the equation in the schematic. These values should give a good linear range. If you have a different value potentiometer just try and keep the ratio roughly the same between it and the resistor.

If you don’t understand the electronic symbols then i strongly recommend you look them up. There are guides out there with pictures instead but you will soon get stuck when it comes to the more advanced circuits.

The pins on the voltage regulator have a 1.7mm spacing so to get them to fit in the strip board i simply bent them as shown here:

Since this is a very simple circuit, i didn’t bother drawing up a circuit layout. I just built it on strip board:

If you look closely in the circuit above, you can see i’ve inserted a small piece of plastic between the regulator and the resistor. This is because they are very close to each other and i was worried about them shorting out. I haven’t attached the heat sink yet, I didn’t need it for testing and i forgot to buy anything to fix it on with.

I tested this circuit by hooking it up to a bench supply at work and testing the output with a multimeter but if you don’t have access to a bench supply, you can power it straight from the atx power supply. Connect the +ve to a yellow 12v wire and the -ve to a black ground wire then short the green wire on the power supply to any black wire. If your supply doesn’t turn on, it may be that you need to draw more current from it. Try attaching a fan, power resistor or old cd drive and trying again. There are many instructions on doing this on the internet, just search for ‘jump start power supply’ on google or follow this link

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