Aug 28 2017

Current pusher

When I etch my own circuit boards, sometimes it happens that there is a very small short on the board. This short is difficult to find. To burn this short away it is handy to have a power supply that can deliver lot of current. My heaviest lab supply however can only supply 6A. Therefore I made this project:

This project is a 5V power supply with an adjustable current limit up to 30A. This power can not be outputted continuously. To make the 5V I used an old ATX PC power supply, these can supply a lot of current on the 5V line.

I have put 12 high power transistors on the secondary side of the power supply to regulate the voltage/current. The transistors are mounted to actively cooled heat sinks. 2 extra power transistors are added to drive the other transistors.

The heat sinks are from 2 old Pentium 2 processors. On top I put a few fans.

I found a few LCD voltmeters in my junk supply. These I have used in this project as volt and ampere meter.

Test layout:


With the switch the output can be enabled. The switch has 3 positions:
-Neutral position = OFF
-Spring return position = output on as long as the switch is activated
-Latch position = output permanent on

The 2 panel meters need their own power supply (isolated voltage), this I solved by adding a small transformer followed by 2 7805 regulators.

This part is the drive circuit of the transistors. This also include the current measurement:


The big pile of resistors are used because the power in the resistors at these currents is very high. I could have used a lower resistance value, but I did not have that in stock. From these resistors I had a partial reel (SMD).

PCB build in:


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