The set of laboratory power supplies (0-30 V, 1 A and ATX)

June 7, 2015
Posted by Michał Drwięga

The presented set of power supplies was made in 2010 and it contains of two devices. One of them is my first electronics construction. The second one is modificated version of unused computer ATX power supply. The following article is focused on the first device what mean power supply with flexible voltage and maximum current fuse.
The assumptions about created power supply were simply: practical construction and low cost.

Descriptrion


The device design based on well known construction from electronics-lab.
Moreover, it was used two gauges based on integrated circuits ICL7107 and fan thermoregulator.

 

power_supply_scheme_1
The scheme of power stage of the device

On the main PCB it was placed auxiliary power supply for fan thermoregulator and gauges. This simply construction consist of a bridge rectifier, capacitors and a voltage stabilizer LM7805.

The fan thermoregulator based on voltage stabilizer LM317 and NTC thermistor placed near to power transistor. The speed of fan and simultaneously the temperature threshold can be changed by specific potentiometer.

power_supply_scheme_2
The scheme of thermoregulator circuit

Voltage and current measurements


The measurement devices are scaled for this application by selection of voltage dividers on inputs. The voltmeter range is from 0 V to 99 V with 0.1 V precision. The range of ammeter is 5 A. The schemes of gauges are shown below.

 

Schemat ideowy woltomierza
The scheme of voltmeter
Schemat ideowy amperomierza
The scheme of ammeter

The case


It was used the case from old ATX power supply. Obviously all unnecessary holes were clogged. The front panel was designed in opensource software GIMP.

Modifications of ATX power supply


In case of ATX power supply modifications include added socket connectors on front panel, LED and power on/off switch. Furthermore, it was shorted specific contacts to force the device start just after connection the power (by front panel switch). In normal operation, the ATX power supply turn on power on outputs when computer motherboard shorted specific outputs (only stand-by voltages are available from power supply start).

Conclusions


After some time I could say that the set of power supplies are very useful and they complement each other but obviously they’re not free of drawbacks. The first device can be used in running new circuits because of current protection. On the other hand, the second one device is suitable for applications with higher power consumption.

Pictures


 

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