The presented set of power supplies was made in 2010 and it contains two devices. One of them is my first electronics construction. The second one is a modified computer ATX power supply. This post is focused on the first device what means power supply with flexible voltage and maximum current fuse.
The assumptions about created power supply were simply: practical construction and low cost.
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.
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 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 the specific potentiometer.
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.
It was used the case from the old ATX power supply. Obviously, all unnecessary holes were clogged. The front panel was designed in open-source software GIMP.
Modifications of ATX power supply
In the case of ATX 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 front panel switch). In normal operation, the ATX power supply turn on the power on outputs when computer motherboard shorted specific outputs (only stand-by voltages are available from the power supply start).
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.