Wall wart power supplies.

Discussion in 'General Electronics Chat' started by hp1729, Dec 23, 2015.

  1. hp1729

    Thread Starter Well-Known Member

    Nov 23, 2015
    They don't have to be the exact voltage and current you need. Keep in mind the unregulated kind will output a higher voltage if ran below the rate current. You can also add a regulator to step or down the output voltage if the wattage is right. I literally have hundreds I have collected over the years. I have no problems powering my projects.
    So ... how do you know if one is regulated? If it is rated at 9 Volts and 100 mA but when you plug it in with no load it is 12 Volts, it is unregulated. That 9 V 100 mA means that at 100 mA it will be 9 V DC. At lower current it will run fine at higher voltages.
    Filter cap or no filter cap? Most have an electrolytic cap of about 100 uF per 100 mA of rated capacity. Power it up, check the voltage. Remove power and see if the output dies immediately (no filter cap) or holds the voltage (cap included).
    Half wave rectification or full wave? You need a scope.

    Handy additions to wall warts. Most exercises or projects need a regulated voltage so you can add a simple voltage regulator as needed to fit your project. A variable output is easy to set up. An op amp and an NPN transistor and a pot is all you need to supply a modest current. For test fixtures I prefer to limit the current at just above the expected level. Just adding two transistors, a few parts and a pot to a regulator may be all you need.

    Fuses or circuit breakers? A good addition. You could also add a current monitor and a latch to a regulator and have an electronic circuit breaker.

    LM317? Good. A variable voltage regulator you can add. One problem is that the output does not normally go down below 1.2 Volts. If you want to go down closer to 0 Volts just take the reference down to -1.2 Volts instead of ground. Minor adjustments to the circuit are required.

    LM723? Ancient but very versatile.

    LM78xx always useful. Keep in mind you don't have to be limited to the rated voltage.