An Isolated Adjustable Auto transformer using microcontroller using atmega


This is a means of testing AC mains operated circuits at variable AC voltages,
and it also provides isolation to allow safe measurements of that circuit.

A fused isolation transformer and a variable auto transformer connected
together in a grounded, fire safe box. What more could you ask?

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I need to be able to test and measure the operation of circuits operating directly from the AC mains, this includes being able to slowly raise the voltage while monitoring circuit performance. This was solved with a variable auto transformer and an isolation transformer. Now, I can choose what part of the AC operated circuit to ground, and connect my oscilloscope directly to the relevant part of the circuit; no more using two probes and doing the old Channel 1 – Channel 2 bit, along with its inherent inaccuracies. The variable transformer allows me to slowly increase the voltage to power supplies under test, so that I can back off on the voltage if signs of malfunction appear.

The Circuit

This is pretty simple: An isolation transformer and a variable auto transformer, very much like a Variac. Fuse 1 protects against gross overload. Lamp 1, across the Fuse 1, is a red incandescent pilot lamp and it lights up in the event of a blown fuse.  Imagine how much time this would save when bringing up a stubborn power supply. Take note: Everything that can possibly come in contact with the user is connected to earth ground. in practice, I also have a earth leakage breaker dongle in series with this device.

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