The presented laboratory power supplies are two separate devices, made in 2010. One of them is the electronic project created from scratch. The second is a modified computer ATX power supply.
The first power supply has an adjustable output voltage and configurable maximum output current.
The major assumptions in the design of the devices were simple. It should be a practical and low-cost project.
Electronic project
The device design is based on the construction from electronics-lab. Moreover, it was equipped with two gauges based on integrated circuits ICL7107 and a fan thermoregulator.
The scheme of the power stage of the device
On the main PCB, it was placed an auxiliary power supply for the fan thermoregulator and gauges. This simple construction consists of a bridge rectifier, capacitors, and a voltage stabilizer LM7805.
The fan thermoregulator is based on voltage stabilizer LM317 and NTC thermistor placed near to power transistor. The speed of the fan and simultaneously the temperature threshold can be changed by the specific potentiometer.
The scheme of the thermoregulator circuit
Voltage and current measurements
The measurement devices are scaled for this application by a selection of voltage dividers on inputs. The voltmeter range is from 0 V to 99 V with 0.1 V precision. The range of the ammeter is 5 A. The schemes of gauges are shown below.
The scheme of the voltmeter
The scheme of the ammeter
The case
The case from the the old ATX power supply has been used. All unnecessary holes were patched with epoxy resin. The front panel was designed in open-source GIMP. Then it was printed and laminated.
Modification of the ATX power supply
In the case of ATX (Advanced Technology eXtended) power supply modifications include added socket connectors on the front panel, LED, and power on/off switch. Furthermore, it was shorted specific contacts to force the device to start just after connecting the power (by the front panel switch). In typical operation, the ATX power supply turns on the power on outputs when the computer motherboard shorts specific outputs (only stand-by voltages are available from the power supply start).
Conclusion
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 device is suitable for applications with higher power consumption.
