# Power Supply circuit needed

Discussion in 'General Electronics Chat' started by mtsago1, Sep 2, 2014.

1. ### mtsago1 Thread Starter New Member

Apr 10, 2013
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mtsago1 said:
hello guys, im a brand newcomer both on the forum and into electronics. i've just grown much interest into electronics and i intend to register with a local university, im in South Africa.
Now, my first project is that i wanna build some mirrored 5mm LEDs to produce an infinity-look like of the LED array. Altogether they are 200 and they draw an average of 20milli-amps at 2.7V each. Now i want to plug it on a 230AC outlet so my problem is on getting the right chip or circuit that can give me that current and voltage, anyone who can help?

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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You are lighting all 200 Leds at the same time?

If so, for safety sake, you need a transformer-isolated DC power supply to start out. Many surplus ACinput-DCoutput regulated power supplies can be obtained cheaply (old computers, monitors, printers, modems, etc, etc). You need one that is capable of greater than 200(0.02*2.7) = 11W.

Say you have on hand a 20W 240Vac-in 15Vdc-out power supply from an old laptop computer... Now it becomes a project to create several parallel strings of series-connected Leds, each string with its own current-limiting resistor. Here is a calculator that shows how that is done. Start by entering the voltage of the supply you can cheaply obtain.

If I was doing this, I would go to my local thrift store (Habitat for Humanity), and could buy a suitable regulated DC supply for \$1US (half the price of a cup of coffee).

I would be looking for a Regulated DC supply with the highest DC output voltage because that will minimize the number of resistors needed in the array. (24V supply better than a 15V supply, for example). Just make sure it is rated for greater than 11Watts output. If the Watt rating is not printed on the supply, multiply the rated output voltage by the rated output current to find the Watts. For example, a supply rated at 20V and 500mA would be only 10W, which is not sufficient for your needs.

Last edited: Sep 2, 2014