The Anti-Latchup Circuit


In electronics, a power supply (for example, battery) usually has a positive line and a negative line. One is not supposed to connect these two with each other because a lot of current flows through and it damages everything. It was in my third semester that I got my very own power supply and it wasn’t long before I accidentally blew it in the above way. So at that time, I started to design a circuit that will provide some protection in such scenarios. But I just lost touch of it as I moved on to other things.

Then the same requirement arose for my second project during my internship at TIMA labs, which specializes in radiation effects on electronics. When electronic components are bombarded with neutrons, it creates faults that is similar to connecting the positive wire to the negative which draws a lot of current damaging the device. This effect is called latchup. To protect both the power supply and the circuit under radiation test, an anti-latchup circuit is needed.

schemeit-project (1)

My Anti-Latchup Circuit

Technically, it is a mix of current sensing and switching techniques with a resistor programmable current limit. For sake of simplicity, let’s skip past that and its working. The power supply, say a battery, is connected to the loose ends on the left and the circuit to be tested is connected to the loose ends on the right. In the absence of this circuit i.e., connecting the battery directly, if a fault happens a large current will be drawn and it can damage the circuit and the battery as well. But with this circuit, the current is never off limits and thus both the circuit and the battery are well protected.

In the video, the black and read wires are the leads that power-up the circuit under radiation test. A fault is artificially created by connecting the two wires and instead of damaging the power supply, the current is moderated at 1 ampere. The rattling sound is due to the relay that is doing the moderation.

I wish I had done this before I blew my power supply, but as the saying goes: it is better late than never.


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