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• MINIATURE ISOLATED AC/DC POWER SUPPLY
  This circuit uses a novel approach to produce a fully isolated and regulated 5 volts @30ma from the 120vac power line. It uses two tiny SCRs that alternately discharge two capacitors through a miniature high frequency transformer. The voltage spikes produced through the transformer are rectified, filtered and regulated. A very common 8-ohm audio impedance matching transformer can be used for the transformer. Published in EDN, Feb. 17, 1992

• LOW POWER 12,000-VOLT POWER SUPPLY
  If you need about 12,000 volts DC for an ion generator this circuit might be the ticket. It draws power from the 120vac power line but it uses a small 6KV camera flash trigger coil. The output signal is isolated from the power line. Although the circuit can only deliver about 5uA of current it can produce dangerous shocks, so be careful.

• CIRCUIT PROTECTS FROM BATTERY POLARITY REVERSAL
  This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was designed for a device powered from a single 1.5 volts button cell battery.  However, the circuit will operate with higher voltages as well.

120 VAC Lamp Dimmer (full wave SCR):  (Circuit / schematic design added 6/06)

120 Volt AC Lamp Dimmer (Full Wave SCR):  (Circuit / schematic design added 6/06)

Circuit Forms Constant Current SCR:  02/01/01 EDN-Design Ideas / (Circuit / schematic design added 6/06)

Nanosecond SCR Switch for Reliable High Current Pulse Generators and Modulators:  MicroNote 601 from Microsem  (app note added 6/06)

SCR phase control yields solid state switch:  03/15/01 EDN-Design Ideas / (Circuit / schematic design added 6/06) SCRs (silicon-controlled rectifiers) / PDF contains multiple circuits - scroll to find the one of interest, or thyristors, have higher current and voltage ratings, lower conduction losses, and more robustness than triacs. For these reasons, SCRs are better suited to high-power applications. This is high power dimmer circuit for115V AC.

SCR Voltage Regulator:  Though not as accurate as a linear or a high-frequency switching regulator, an SCR voltage regulator wastes little power and creates no RFI.  Designed by Andrew R. Morris  (added 09/05)

Silicon Controlled Rectifier Model Railroad Throttles and London Model Railroad Group SCR Throttle:  The following is a schematic drawing of a Silicon Controlled Rectifier type throttle for use on larger scale model railroads. Three versions of this throttle are shown on this page. They are not sophisticated designs but work well and are tough and reliable. (added 2/05)

Thermostat for 1KW Space Heater (SCR controlled):  Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts. The relay contacts should be rated above the current requirements for the heater. Temperature changes are detected by a (1.7K @ 70F) thermistor placed in series with a 5K potentiometer which produces about 50 millivolts per degree F at the input of the LM339 voltage comparator. The two 1K resistors connected to pin 7 set the reference voltage at half the supply voltage and the hysteresis range to about 3 degrees or 150 millivolts. The hysteresis range (temperature range where the relay engages and disengages) can be adjusted with the 10K resistor between pins 1 and 7. A higher value will narrow the range....   (Circuit / schematic design added 6/06)