technique_valley

This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range. It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall poweradapter power supply.

This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding.  The transformer contains a single turn primary with a low 0.001-ohm resistance.  It can easily handle 30 Amps of AC current and provides at least 500vac of isolation.  With the components shown, the output AC voltage is scaled so 1 Amp of current produces 100mv of AC voltage.

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistanceso it doesn't generate very much heat. The circuit was designed to provide a cheap, compact power supply for Cmos logic circuits that require only a few milliamps. The logic circuits were then used to control mains equipment, using an optically-isolated triac.

This circuit injects an adjustable current through a wire loop.  Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps.

In electronics, it is often handy to have a fully isolated variable AC power supply.  With such a device you can safely test various AC powered circuits and even probe around in the circuit with an oscilloscope. The hobby circuit below was designed to provide up to 500 watts of AC over a range of zero volts to over 250vac.  For safety, it is designed with two separate outputs.  One output ranges from zero to about 140vac.  The second output ranges from zero to over 250vac.  Different sockets are used, so a standard 120vac device can’t be accidentally plugged into the higher voltage socket.  An AC volt meter and an AC current meter could be included if desired as shown in the photo below.  A three position left off toggle switch is uses on conjunction with a power relay to route power to the app...