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Aug 28

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.

http://image.elektronicastynus.be/85/1414616491.jpg

http://image.elektronicastynus.be/85/1414616423.jpg

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.

http://image.elektronicastynus.be/85/1414616483.jpg

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

http://image.elektronicastynus.be/85/1414616496.jpg

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

Test layout:
http://image.elektronicastynus.be/85/1414616716.jpg

Mounted:

http://image.elektronicastynus.be/85/1414616711.jpg

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.

http://image.elektronicastynus.be/85/1414616720.jpg

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

Circuit:

http://image.elektronicastynus.be/85/Schema.gif

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).

http://image.elektronicastynus.be/85/1414618300.jpg

http://image.elektronicastynus.be/85/1414618203.jpg

PCB build in:

http://image.elektronicastynus.be/85/1414618496.jpg

http://image.elektronicastynus.be/85/1414618503.jpg

http://image.elektronicastynus.be/85/1414618479.jpg

Ready:

http://image.elektronicastynus.be/85/1414618459.jpg

http://image.elektronicastynus.be/85/1414618490.jpg

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