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...

The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.

The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line.

I’ve been having a problem with my instant hot water system lately.  This system circulates electrically heated water throughout my house using a small pump.  The pump is wired into a ground fault interrupter (GFI) module.  Every now and then, the GFI trips, leaving me without hot water.  What I need is an alarm to tell me when AC power on that outlet has been turned off by the GFI.  I figured a 9v battery powered loud chirping beeper would be the ticket for this kind of alarm. The chirping sound would draw my attention and let me know that I need to reset the GFI switch, without waking the whole neighborhood.  as circuit is shown below.

If you wish to test a line-powered device under both a 15% high and a 15% low voltage condition, you can use the circuit below.  The circuit uses an 18v transformer with a 3 Amp rating.  A double pole, double throw toggle switch then switches in the transformer voltage in either a buck or a boost mode.  In the buck mode, the transformer voltage is subtracted from the line voltage.  In the boost mode, the transformer voltage is added to the line voltage.  With an 18vac transformer the normal 120vac voltage is switched between 102vac and 138vac. For 240vac power line tests, use a 36vac transformer rated at 2A.

Power lines, which deviate much beyond normal voltages can damage expensive electronic equipment.  This hobby circuit below sounds an alarm whenever the line voltage is higher or lower than normal.  I set the alarm limits at about +-15% from standard levels.  This hobby circuit rectifies and filters the power line signal.  I set the resistor values, so the DC voltage produced is close to 1% of the RMS value of the line.  Thus, a 120vac line would yield about 1.2v DC.  That voltage is fed to a pair of voltage comparators.

This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line.  This hobby circuit.  

Most solid state relays require at least 5ma and often more input control current, to fully turn on the device.  But such current levels often force battery powered circuits to use excessively large batteries.  The relay hobby circuit shown below demands only 50uA of input current.

Some of the latest LEDs are amazing.  They can produce a surprising amount of light with very little current.  In the light flasher application shown below I take advantage of a nice surface mounted LED from King Bright.  This flasher circuit draws only about 3ua of average current from the AC power line to flash this green LED.  This flasher might be used as a power indicator light.

This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac.