The post describes a simple but extremely versatile 100 amp, variable voltage power supply circuit using just a few BJTs in parallel and in a common collector mode. The idea was requested by Mr. Andre.
The Circuit Request
Hello Swagatam, I was wondering if you could possibly assist me. on the blogs I have seen some diagrams for simple variable power supplies.
Firstly I know very little about electronics, but with a shopping list and a diagram I am sure I would be okay.
I would like to build a simple variable power supply with an input of 220/240 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A.
I have started zinc electroplating as a hobby (have sweaty hands and want to protect all my tools) the chemical company gave me these as a more or less dependant on my zinc plating bath size.
At the moment the little 6V 8A Ryobi battery charger works for a few minutes, overheats and cuts out till it cools down again. I would really appreciate any assistance you could give me on this.
The Circuit Design
A very straightforward circuit design for the proposed 100 amp variable voltage power supply can be witnessed in the following diagram.
The design basically utilizes a common collector or an emitter follower topology for implementing the operations, by incorporating just a few Darlington power transistors, some resistors and a pot for varying the output voltage.
As can be seen in the diagram, the collectors and the emitters are all joined in common across each other while the bases are made into a common line via individual limiting resistors.
The free ends of these resistors are joined together with a pot across the negative line of the circuit, which determines the voltage regulation at the output of the circuit.
For acquiring more current, more number of transistors may be added in the design, and for reducing the output amps, these may be simply deducted from the configuration.
For inputs above 50V the pot must be upgraded to a high wattage type to sustain the high voltage across its terminals.
All the power devices must be mounted over a common aluminum heatsink without any mica isolation, so that the dissipation is shared uniformly across all the devices and a thermal runaway situation is prevented.