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Circuits designed by David Johnson, P.E.
Last Updated on: Monday, July 11, 2016 01:59 PM

Master Category List - Dave's Circuits

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Variable Power Supply Circuits

0VAC to 280VAC Variable Isolated AC Voltage  -  I designed and built this circuit about 25 years ago. It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC. It provides complete isolation from the power line. It uses two 1:1 isolation transformers that are wired in parallel . . . [Hobby Circuit designed by David Johnson P.E.,  07/08/00]


12v – 24v AC and DC Day/Night Switch  -  The circuit uses a bridge rectifier circuit to convert AC into DC.  A 12v zener diode limits the operating voltage of the circuit to 12v.  A tiny Schmitt trigger inverter and a phototransistor detects the ambient light intensity.  If there is sufficient light, the inverter disables a push-pull oscillator circuit . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/25/12]


240VAC to 5VDC Power Supply  -  This is simple way to power some 5v logic from a 240vac source.  If a 120vac power adapter is used, the circuit will also work for 120vac power lines . . . [Circuit by David Johnson P.E.,  02/12/02]

 

9v Battery Eliminator  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the circuit . . . [Circuit by David Johnson P.E.,  12/06/09]


AC to DC (240v to 5v)Power Supply  -  This is simple way to power some 5v logic from a 240vac source.  If a 120vac power adapter is used, the circuit will also work for 120vac power lines . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/12/02]


Battery Eliminator  -  If you use a 1.5v or a 3v battery powered MP3 player for long periods of time, you may get tired of constantly changing batteries. Some older players do not work will NiMH rechargeable batteries so changing out batteries can get expensive.  The circuit be . . . [Circuit by David A. Johnson P.E.,  06/01/05]


Circuit Eliminates 9v Battery  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the c . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/06/09]


LM317 adjustable voltage regulator used in Battery Eliminator Circuit  -  If you use a 1.5v or a 3v battery powered MP3 player for long periods of time, you may get tired of constantly changing batteries. Some older players do not work will NiMH rechargeable batteries so changing out batteries can get expensive.  The circuit be . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/01/05]


Nine-Volt Battery Eliminator  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the circuit . . . [Circuit by David A. Johnson P.E.,  12/06/09]


Touch Switch 240VAC  -  This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/12/02]


Variable Isolated AC Voltage Spans 0Vac to 280Vac  -  I designed and built this circuit about 25 years ago. It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC. It provides complete isolation from the power line. It uses two 1:1 isolation transformers that are wired in parallel . . . [Circuit by David A. Johnson P.E.,  07/09/00]


Voltage Boost  -  In this design a marginal AC to DC linear power supply provides a voltage boost, so it can maintain regulation at low line voltages.  The added components are wired at the AC input and the + DC output of an existing bridge rectifier circuit. The components act as a full wave “charge pump” which will boost the DC output voltage across the main filter capacitor C3. Without the boost circuit, when the AC line voltage drops to 105vac, the DC output voltage only reaches 11.5 volts, too low for a 12v voltage regulator. . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/18/06]


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