# 5-12V 200mA Regulated Power supply

Posted on Nov 22, 2012

It will accept AC from 6v to 18v or DC from 9v to 18v and any current up to 1 amp. The diode bridge on the input converts AC to DC and it doesn't matter which way around the leads are connected as the diodes compensate for either direction. If a DC plug pack is used, the bridge can be left out and the leads taken directly to the positive and negative of the 1,000u electrolytic. If you use the bridge, no damage will result, however about 1.2v will be lost across it and this may reduce the output a little. The 1,000u electrolytic is suitable for currents up to 500mA and if you want to use an 800mA or 1 amp plug pack, you will have to replace it with a 2,200u or add another 1,000u. The circuit contains 2 indicator LEDs. The green LED is POWER ON` and the red LED indicates

"DROPOUT." This LED lets you know when you are drawing too much current or the output is shorted. It turns on when the output is less than 3v. The other feature of this circuit is the variable output voltage. It can be adjusted from 5v to 9v (or 12v) and the board contains a simple scale around the 500R pot so that the pointer on the shaft will indicate the approximate voltage. The regulator is a 7805 and this is a 5v type. The principle of operation of these 3-terminal devices is the output is always 5v higher than the "ground" lead. Click HERE for a discussion on the 3-terminal regulator. If we "jack up" the ground lead, the output will rise also. This is how we get voltages higher than 5v. But there is one thing that's most important. It's heat-sinking the regulator. The heat generated by the regulator is a product of the voltage across it and the current flowing. As an example, at 300mA and 12v out, the voltage across the regulator will be at least 3v (3v is the minimum across the regulator to prevent it dropping out of regulation), making the heat generated about 3 x 0.3 = 0.9 watts (900mW). The heat-sink supplied in the kit is capable of dissipating 3 watts so we are below the maximum in this case. But when the output is 5v and 300mA is flowing, the voltage across the regulator is 10v x 0.3A = 3 watts and the chip may start to heat up to a point where the thermal shut down feature will come into operation....

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