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A 5 Volt power supply.

Benny Peter Jørgensen

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This week I have made a 5 V regulator. Many of you people out there uses a 7805 to achieve 5 V for the logic and MCU's on our robot's, but a 7805 needs at least 9 V to function and I use a 7.2 V battery. Therefore I have made this little construction. The word "little" must have it's right here because it only uses 4 resistors, 3 transistor's, a capacitor and a zener diode. There is an trim resistor, to adjust the output to 5 V. Remember to adjust it to 5 V before connection any electronic to it. Using this trimmer the output voltage can be adjusted from 4 V and up to input voltage. If, on the other hand, the trimmer stops working the output voltage will be around 2.7 V and therefore not harming sensitive electronic.

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As can be seen on the graph, it delivers out 4.94 V at 150mA load, using only 5.50 V. At 500 mA output it needs at least 6.5 V to function properly. If you need high (½ A to 2 A) output current it can be a grate thin to change the 470 ohm connected between the ground and the BC547 to 220 ohm or 330 ohm. Also change the BD136 to BD238, for lower Vce saturation. I haven't tried it, so here is no guarantee.

The regulator itself uses 15 mA of current. Using an other FET might lower this. The FET can also be replaced by a resistor of 2.2 Kohm, but it will harm the performance. Then output voltage will dependent on the input voltage. If adjusted to 5 V out at 7.2 V in, it will deliver 5.25 V out at 9.5 V in and only 4.7 V out at 5.5 V in. If you want to save approx. 6 mA and if you battery supply delivers a constant voltage, then change the resistor.