Symmetrical power supply 1,25-17V 3A

Presented here symmetrical power supply is a small, simple and powerful item. It can be both taken to workplace from home and used in different conditions. The construction was to be resistant to mechanical damage and to have thermal and current endurance of good parameters. All that was ensured by simplicity of construction and choice of materials used. The quality of stabilization was also important issue.

LM317 is a simple, speed, resistant and good stabilizer. There is also LM337, but it is negative section. Both of them are controlled by a common potentiometer. Schematic is direct configuration from the note sheet. Of course, the circuit without any additional components can not cope with such a load. Thus, the device uses two TIP35/36C. Voltmeter was made of a standard Jabel kit. Current measure was made of LM3914 and shunt 0,05ohm. Bridge rectifier consists of four diodes BDY35. The original housing included a transformer, but it needed to be rewind. Originally it had 2x11,7V, but it turned out that after filtration and under the load, stabilizers fall into overdrive at 13V. The voltage had to be increased, so it was rewind to 2x17V by a wire 1,6mm and additional winding was applied for the voltmeter and ammeter 7V. The current indicator was scaled 200mA/segment.

The power supply work is very satisfactory even when it exceeds the range of indicator. When loaded with two car bulbs, with connected both fibers in parallel, it was tested for 20 minutes at a voltage of 12V. Transformer gave sound and the temperature of heat sinks reached even 80 degrees Celsius. Despite all that, the power supply worked correctly.

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When fully loaded, the heat sink heat up significantly, but this could not possibly damage the construction. Start up should not be problematic. When the voltmeter does not work as it is desired to do, adding a capacitor from the main board 1000uF/6,3V can help to overcome this. The device uses a knob from Radmor 5102.

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