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Last Updated: December 01, 2017 03:41 AM

Circuits Designed by Dave Johnson, P.E.

12 Volt Lite/Dark Lamp SwitchOften, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector. . . . Hobby Circuit designed by David Johnson P.E.-June, 2008

120 VAC Low Voltage AlarmThis circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac.. . . Circuit by David Johnson P.E.-July, 2006

12v Brush Motor Speed ControllerIn many applications, you would like to hold the speed of a motor constant, even as variations in the power supply voltage or mechanical load try to change its speed.  In other applications, the average current to the motor needs to be limited, so the . . . Hobby Circuit designed by Dave Johnson P.E.-May, 2007

12v Cooling Fan ThermostatThis 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 Dave Johnson P.E.-February, 2011

12v DC Motor with Logic Controlled Automatic BrakeThere are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  When the input logic signal swings from 0v to +5v, the n-channel . . . Hobby Circuit designed by David Johnson P.E.-February, 2010

12v Light/Dark Lamp SwitchAt night, this circuit will route current to a 12v lamp, turning it on. . . Circuit by Dave Johnson P.E.-July, 2006

12v Touch Switch Exciter CircuitThis circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.    It can support a cable length of about 2500 feet.    A typical remote switch circuit is also shown as well as a receiver circuit for those switches.. . . Circuit by David Johnson P.E.-February, 2002


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

12 Volt 20 Amp Solar Charge Controller (kit available) -  The SCC3 is a solar charge controller, its function is to regulate the power flowing from a photovoltaic panel into a rechargeable battery.  It features easy setup with one potentiometer for the float voltage adjustment and an equalize function for periodic overcharging.  Automatic temperature compensation optimizes battery charging over a wide range of temperatures.  The SCC3 is robust, it can handle reverse polarity connection of both the battery and photovoltaic panel.   __ Designed by G. Forrest Cook

12 Volt Differential Temperature Controller -  for hot water and hot air system control __ Designed by G. Forrest Cook

12 Volt Lamp Dimmer (using a pot) -  Here is a 12 volt / 2 amp lamp dimmer that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of a astable 555 timer oscillator.  When the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistor __ Designed by Bill Bowden

12 Volt Lamp Fader (LEDs or incandescent) -  This circuit is similar to the "Fading Red Eyes" circuit   (in the LED section) used to fade a pair of red LEDs.  In this version, the lamps are faded by varying the duty cycle so that higher power incandescent lamps can be used without much power loss.  The switching waveform is generated by comparing two linear ramps  __ Designed by Bill Bowden

12 Volt Lite/Dark Lamp Switch -  Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector. . . . Hobby Circuit designed by David Johnson P.E.-June, 2008

1212 Volt Strobe -  Strobes are useful devices for seeing fast moving components freeze or just as lighting effects.  Unfortunately for a really good result you need to use a Xenon flash tube which can produce intense brief discharges of light but it needs high trigger voltages upwards of 4KV!  __ Designed by Phil Townshend 2012

12 Volt Strobe, Coil Driven -  This circuit will give provide a Good Strobe Effect for a variety of
Portable Uses.  Nominal current draw is "up to about" 1 amp at 12 volts.  Depending on value of capacitor on pin 2 of the 555 and the particular choke that is used.  The .01 cap on pin 2 of the 555 may be slightly changed in value to optomize the output drive to the 22 mfd capacitor.   __ Designed by G.L. Chemelec

12/24V Auxiliary Battery Controller -  Going bush in the 4WD or camper? Want to add a second battery for security and safety? Here's the safe way to do it.__ SiliconChip

12/24V MPPT Solar Charge Controller Rev.1 -  Mix-It: An Easy-To Build 4-Channel Mixer__ SiliconChip

120 VAC Lamp Chaser using Solid State Relays -  This circuit is basically the same as the 10 channel LED sequencer with the addition of solid state relays to control the AC lamps.  The relay shown in the diagram is a Radio Shack 3 amp unit   (part no.275-310) that requires 1.2 volts DC to activate.  No current spec was given but I assume it needs just a few __ Designed by Bill Bowden

120 VAC Lamp Dimmer -  The full wave phase control circuit below was found in a RCA power circuits book from 1969.  The load is placed in series with the AC line and the four diodes provide a full wave rectified voltage to the anode of a SCR.  Two small signal transistors are connected in a switch configuration so that when the voltage on the 2.2uF __ Designed by Bill Bowden

120 VAC Low Voltage Alarm -  This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac.. . . Circuit by David Johnson P.E.-July, 2006

120 Volt AC Lamp Chaser using Solid State Relays -  This circuit is similar toLED clock using12 neon indicator lamps instead of LEDs.  It operates from2 high capacity ni-cad cells   (2.5 volts) which keep it going for a couple weeks.  High voltage   (70 volts) forneon lamps is obtained from a small __ Designed by Bill Bowden

120 Volt AC Lamp Dimmer Full Wave SCR -  The full wave phase control circuit below was found in a RCA power circuits book from 1969.  The load is placed in series with the AC line and the four diodes provide a full wave rectified voltage to the anode of a SCR.  Two small signal transistors are connected in a switch configuration so that when the voltage on the 2.2uF capacitor reaches about 8 volts, the transistors will switch on and discharge the capacitor through the SCR gate causing it to begin conducting.  The time delay from the beginning of each half cycle to the point where the SCR switches on is controlled by the 50K resistor which adjusts the time required for the 2uF capacitor to charge to 8 volts.  As the resistance is reduced, the time is reduced and the SCR will conduct earlier during each half cycle which applies a greater average voltage across the load.  With the resistance set to minimum the SCR will trigger when the voltage rises to about 40 volts or 15 degrees into the cycle.   __ Designed by Bill Bowden

120VAC Lamp Chaser using Solid State Relays -  This circuit is basically the same as the 10 channel LED sequencer with the addition of solid state relays to control the AC lamps.  The relay shown in the diagram is a Radio Shack 3 amp unit   (part no.275-310) that requires 1.2 volts DC to activate.  No current spec was given but I assume it needs just a few __ Designed by Bill Bowden

12-channel Infrared Remote Control -  It uses an infrared remote control unit and can switch 12 circuits, all either momentary or latched.__ SiliconChip

12V 1.5A Buck Regulator with Virtual Remote Sense -  The LT4180 solves the problem of providing tight load regulation over long, highly resistive cables without requiring an additional pair of remote sense wires.  This Virtual Remote Sense device continuously interrogates the line impedance and corrects the power supply output voltage via its feedback loop to maintain a steady voltage at the load regardless of current changes__ Linear Technology/Analog Devices App Note, Jun 7th 2010

12V 20A Solar Charge Controller -  The SCC3 kit is the heart of a 12 Volt solar power system, it regulates the charging of batteries from photovoltaic   (PV) solar panels.  A charge controller is an essential part of any solar power system.  A 12 Volt solar power system can provide power to a wide variety of devices such as lighting systems, Ham and CB radios, car stereos, cell phone chargers, laptop computers, televisions, recording equipment, fans, water pumps and other 12V DC loads.  With the addition of a DC to AC inverter, the DC power can be converted to 120 Volts AC for running many household electronic devices. 
 __ Designed by G. Forrest Cook

12v Brush Motor Speed Controller -  In many applications, you would like to hold the speed of a motor constant, even as variations in the power supply voltage or mechanical load try to change its speed.  In other applications, the average current to the motor needs to be limited, so the . . . Hobby Circuit designed by Dave Johnson P.E.-May, 2007

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 Dave Johnson P.E.-February, 2011

12v DC Motor with Logic Controlled Automatic Brake -  There are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  When the input logic signal swings from 0v to +5v, the n-channel . . . Hobby Circuit designed by David Johnson P.E.-February, 2010

12V Distribution in μTCA Redundant Power SubsystE - M -  The LTC4225 offers ideal diode and Hot Swap functions for two power rails by controlling external series connected N-channel MOSFETs.  MOSFETs acting as ideal diodes replace two high power Schottky diodes and the associated heat sinks, saving power and board area.  Hot Swap control MOSFETs allow boards to be safely inserted__ Linear Technology/Analog Devices App Note, Apr 22, 2011

12V Flourescent Lamp Inverter -  Drive a standard 36/40W fluoro tube to fll brightness from a 12V DC.  Ideal for camping, a trouble light or even emergency home lighting.__ SiliconChip

12V Fluorescent Inverter -  This is a low-cost project for 20 or 40 watt fluorescent tubes.  However the most efficient is to use a 40 watt tube   (or two 20 watt tubes in series).  It's a circuit you can put together from junk box components or build from a kit.  It's very simple to build and requires no printed circuit board __ Designed by Collin Mitchell

12V LDO Solar Charge Controller -  This Low Dropout Voltage   (LDO) solar charge controller uses a simple differential amplifier and series P channel MOSFET linear regulator—their compatibility seems like a marriage made in heaven.  Voltage output is adjustable.  It is mainly intended for charging 12V lead-acid batteries.  Solar Charge Controller Specifications __ Designed by Jim Keith

12v Light Dimmer V2 -  This version controls lights, LEDs and even motors with only 10 componentsup to 50W __ Contact: P. Townshend EduTek Ltd

12v Light/Dark Lamp Switch -  At night, this circuit will route current to a 12v lamp, turning it on. . . Circuit by Dave Johnson P.E.-July, 2006

12V PWM Motor/Light Controller -  The diagrams are for 12V operation only and there are high side   (common ground) and low side   (common +12V) versions.  The low side version of the circuit uses an N Channel FET, the high side version of the circuit uses a P Channel FET.  N Channel devices tend to handle more current than P Channel devices, they are also less expensive.  The high side version of the circuit is useful when one side of the load has to be grounded __ Designed by G. Forrest Cook

12V Speed Controller/Lamp Dimmer -  This handy circuit can be used as a speed controller for a 12V motor rated up to 5A   (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W.  It varies the power to the load   (motor or lamp) using pulse width modulation   (PWM) at a pulse frequency of around 220Hz.__ SiliconChip

12v Touch Switch Exciter Circuit -  This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.    It can support a cable length of about 2500 feet.    A typical remote switch circuit is also shown as well as a receiver circuit for those switches.. . . Circuit by David Johnson P.E.-February, 2002

12V, 10A Load Share -  The LTC4370 is a two-supply current sharing controller which incorporates MOSFET ideal diodes.  The diodes block reverse and shoot-through currents during start-up and fault conditions.  Their forward voltage is adjusted to share the load currents between supplies.  Unlike other sharing methods, neither a share bus nor trim pins__ Linear Technology/Analog Devices App Note, Jun 19th 2013

12V/5A Output from 4V-38V Automotive Input Supply -  The LTC3789 is a high performance buck-boost switching regulator controller that operates from input voltages above, below or equal to the output voltage.  The constant-frequency, current mode architecture allows a phase-lockable frequency of up to 600kHz, while an output current feedback loop provides support for battery charging.  With a wide 4V to 38V   (40V maximum) input and output range and seamless, low noise transitions between operating regions, the LTC3789 is ideal for automotive, telecom and battery-powered systems__ Linear Technology/Analog Devices App Note,, Dec 22, 2010

12V-24V High-Current DC Motor Speed Controller, Pt.1 -  This 12V or 24V high-current DC Motor Speed Controller is rated at up to 40A   (continuous) and is suitable for heavy-duty motor applications.  All control tasks are monitored by a microcontroller and as a result, the list of features is extensive.__ SiliconChip

12V-24V High-Current Motor Speed Controller -  Last month, we described the circuit and software features of our new High-Current DC Motor Speed Controller.  This month, we show you how to build and test it.__ SiliconChip

12VDC Fluorescent Lamp Driver -  This fluorescent lamp driver uses a normal 120 to 6V step-down transformer in reverse to step12V to about350-Volt to drive a lamp without need to warm filaments.   __ Designed by Aaron Cake

12VDC Sump Pump Control -  A simple control to turn on and off a 12v DC sump pump   (like a boat bilge pump) as water level rises in the sump.   __ Designed by Burton Lang

12Vin to 5V AT 25A using Very Low DCR Current Sense -  The LTC3866 is especially well suited to low voltage, high current supplies because of a unique architecture that enhances the signal-to-noise ratio of the current sense circuit.  This allows it to operate with the small sense signals produced by very low DCR, 1mΩ or less, inductors, which are used to improve power efficiency in high current supplies.  The improved SNR minimizes jitter due to the switching noise, which could corrupt the signal.  The LTC3866 can sense a DCR value as low as 0.2mΩ with careful PCB layout__ Linear Technology/Analog Devices App Note, Mar 29th 2012

12-volt Cellar Drain Pump -  This circuit lets you control a pump, to keep the level of water in a cellar below a certain threshold, for example.  Power is supplied to the pump by a battery that is recharged automatically when the AC powerline voltage is present requires login to see circuit __ Designed by Published in Elecktor July/Aug, 2010

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Control Circuits:   #'s - A       B - C       D - G        H - L       M - P        Q - S        T - U        V - Z


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