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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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Silicon Controlled Rectifier (SCR) Circuits
SCR Circuits designed by Dave Johnson:
Page 1,  Page 2

10mhz to 20mhz Laser Light Detector  -  This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system. It has good ambient light immunity . . . [Circuit by David Johnson P.E.,  06/14/00]


12kv 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 . . . [Circuit by David A. Johnson P.E.,  03/27/99]

12v Cooling Fan Thermostat  -  This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level.  Both the high and low temperatures are both adjustable . . . [Circuit by David A. Johnson P.E.,  02/06/11]


18v AC to DC Power Supply  -  This is a classic linear power supply which produces a regulated 18v, rated at about 1 Amp . . . [Circuit by David Johnson P.E.,  07/09/06]


24 Volts AC to 24 Volts DC Power Supply  -  The idea for the circuit below came from a company needing to power several 24v DC LED assemblies from an existing 24vac supply.  They did not need a rock solid and regulated 24 volts but a voltage which hovered around that voltage.  Running the AC through . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/20/11]


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 Dave Johnson P.E.,  02/12/02]


24V DC Powered Beeper with 4 Separate Inputs  -  24vac is a popular voltage.  It is often used in low voltage lighting systems and industrial controls.  It is much less dangerous than 120vac/240vac line voltages.  This hobby circuit below is one method to efficiently power a cluster of 7 white LEDs from 24vac. . . . [Hobby Circuit designed by Dave Johnson P.E.,  12/19/09]


24-Volt AC Powered Isolated +5V Supply  -  24vac is a very popular power supply in many industrial systems.  It is often used in systems that involve water.  It is also popular with many inside and outside lighting systems.  The lower voltage means the danger of human electrocution is much less.   . . . [Hobby Circuit designed by David Johnson P.E.,  07/29/09]


4-20ma Current Loop Tester  -  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 . . . [Circuit by Dave Johnson P.E.,  05/01/12]


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 A. Johnson P.E.,  12/06/09]


A Current Transformer used to Harvest Energy  -  Energy harvesting is all the rage these days.  With some modern electronics, information from low power sensors can be sent to a distant data collection point using a low power RF transmitter.  To power these remote sensors, various energy sources can be . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/17/10]


AC Current Monitor  -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/10/06]


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 Johnson P.E.,  02/12/02]


AC to DC 18V Power Supply  -  This is a classic linear power supply which produces a regulated 18v, rated at about 1 Amp . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/09/06]


AC to DC Power Supply requires Low Power  -  Last month I showed how to use a small common mode choke as a fully isolated transformer and a 130v sidac to generate about 100mw of DC power from the AC line.  This second circuit still uses the same inexpensive tiny off-the-shelf 5mH common mode filter coil with a split bobbin as a high frequency transformer but uses two SCRs instead of a sidac to discharge a capacitor . . . [Hobby Circuit designed by David Johnson P.E.,  11/20/11]


AC/DC relay from Charge Coupled MOSFET  -  This circuit acts as an AC/DC relay with a rating up to 50 volts peak and up to 10 Amps of current.  The differential oscillator supplies voltage to the gates of the two FETs with good isolation will drawing only 1.5ma of current . . . [Hobby Circuit designed by David A. Johnson P.E.,  10/16/05]


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 Johnson P.E.,  06/01/05]

 

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