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AC Power Control Circuits
Last Updated on: Monday, March 09, 2015 08:15 AM

Circuits Designed by Dave Johnson, P.E. :
  • 50ua Current Drives Solid State Relay Requires Only -  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…[Hobby Circuit designed by Dave Johnson P.E., 1998]
     
  • AC Line Under/Over Voltage Alarm -  Power lines, which deviate much beyond normal voltages can damage expensive electronic equipment.  The 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…[Hobby Circuit designed by Dave Johnson P.E., 5/01/2005]

  • AC Power Line High/Low Voltage Tester -  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…[Circuit designed by David A. Johnson P.E., 5/01/2005]

  • AC Power Loss Alarm -  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…[Circuit designed by Dave Johnson P.E., 7/29/2012]

  • Active AC Power Line Indicator -  The circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  I…[Circuit designed by David A. Johnson P.E., 5/02/2005]

  • Bi-Directional Charge Coupled Powers MOSFET Relay -  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…[Hobby Circuit designed by Dave Johnson P.E., 1999]

  • Charge Coupled Bi-Directional Power MOSFET Relay -  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…[Circuit designed by Dave Johnson P.E., 1998]

  • High/Low Voltage Tester on AC Power Line  -  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…[Hobby Circuit designed by Dave Johnson P.E., 5/01/2005]

  • Hot AC Power Line Indicator -  The circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  I…[Hobby Circuit designed by David A. Johnson P.E., 5/01/2005]

  • Line Powered High Intensity LED Flasher -  There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with…[Hobby Circuit designed by David A. Johnson P.E., 4/05]

  • Line Powered White LED Array -  There has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed…[Circuit designed by David A. Johnson P.E., 2/28/2010]

  • Solid State Relay Requires Only 50ua Drive Current -  This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR…[Circuit designed by David A. Johnson P.E., 1998]

  • SSR Requires Ultra Low Control Current -  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…[Hobby Circuit designed by David A. Johnson P.E., 1998]

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

125khz Oscillator with Medium Power -  This circuit adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz... [Hobby Circuit designed by David A. Johnson P.E., 3/12/02]

5.8 watt audio power amplifier -  A simple and very cheap audio power amplifier… [Name of Designer is not included]

50ua Current Drives Solid State Relay Requires Only -  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... [Hobby Circuit designed by David A. Johnson P.E., 6/03/00]

AC Line Powered LED Flasher -  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... [Hobby Circuit designed by David Johnson P.E., 12/07/08]

AC Line Powered LED Strings -  This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line.  This hobby circuit was designed by Ken Schultz. …[Circuit by David A. Johnson P.E., 12/18/04]

AC Line Powered LED Strings -  This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line.  This hobby circuit was designed by Ken Schultz. …[Circuit by David A. Johnson P.E., 12/18/04]

AC Line Powered LED Strings -  This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line. … [Designed by Ken Schultz, drawn by Dave Johnson 12.18.2004]

AC Line Under/Over Voltage Alarm -  Power lines, which deviate much beyond normal voltages can damage expensive electronic equipment.  The 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…[Hobby Circuit designed by David Johnson P.E., 3/29/09]

AC Power Line High/Low Voltage Tester -  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... [Hobby Circuit designed by David Johnson P.E., 3/14/10]

AC Power Loss Alarm -  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... [Hobby Circuit designed by David A. Johnson P.E., 3/29/09]

AC power supply -  I have done a lot of work with valves in recent years. For me valves have many advantages, least of all the price; since they are now "obsolete" it is quite easy to get hold of them for next to nothing at rally's and junk sales. I recently purchased a couple of hundred battery valves for less than SEK1 (GBœ0.10 US$0.15) each. … [Harry, SM0VPO Email: harold.lythall @ era.ericsson.se]

AC-power monitor uses remote sensing -  04/26/01 EDN Design Idea   The detection circuit in the Design Idea   "Circuit monitors ac-power loss" (EDN , Nov 24, 1999, pg 172) requires a physical connection with the mains to sense the power loss. The circuit in Figure 1 senses the power loss through the… [by Sanjay R Chendvankar, Tata Institute of Fundamental Research, Colaba, Mumbai, India]

AC-power your circuit without a transformer -  07/17/13  EDN Design Idea    Editor's Note: Here's another take on the transformerless AC line power supply, which finds use in some well-insulated, low-power devices. Our technical reviewer pointed out that Cac should be an X-rated safety type, and I think we'd both feel better if the ground symbol wasn't there!  SMPS circuits offer an efficient way to reduce AC from a mains source to any desired level for powering low-voltage circuits, though this comes at the cost of components such as control ICs, switching transistors, inductors, etc. Figure 1 shows a simple way you can use more common components to step-down and regulate the AC mains to the desired low DC voltage. … [by Raju Baddi]

Active AC Power Line Indicator -  The circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  I... [Circuit by David A. Johnson P.E., 5/02/05]

Bi-Directional Charge Coupled Powers MOSFET Relay -  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... [Circuit by David A. Johnson P.E., 6/03/00]

Charge Coupled Bi-Directional Power MOSFET Relay -  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... [Circuit by David A. Johnson P.E., 6/03/00]

Circuit Level-Shifts AC Signals -  10-Jul-03 EDN Design Idea   AC signals can emanate from many sources, and many of these sources are incompatible with the most popular interface voltages, such as TTL. A temptation always exists to capacitively couple the ac signals because capacitive couplin… [by Ron Mancini, Texas Instruments, Bushnell, FL]

Circuit tests the self-resonance frequency -  This circuit tests the self-resonance frequency is of an inductor. During the test, only a few picofarads of parallel capacitance are added to the inductor.  When connected to an oscilloscope and a signal generator, you can measure resonant frequencies... [Circuit by Dave Johnson P.E., 6/09/00]

High Intensity Line Powered LED Flasher -  There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with... [Circuit by David Johnson P.E., 12/07/08]

High/Low Voltage Tester on AC Power Line  -  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... [Hobby Circuit designed by David A. Johnson P.E., 3/14/10]

Hot AC Power Line Indicator -  The circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  I... [Hobby Circuit designed by David Johnson P.E., 5/02/05]

Indicator for Acceptable Voltage -  I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is... [Hobby Circuit designed by Dave Johnson P.E., 2/09/02]

Inductor Self-Resonance Tester -  If you want to know what the self-resonance frequency is of an inductor, this circuit will help. It adds only a few picofarads of parallel capacitance to the inductor under test. With the aid of an oscilloscope and a signal generator this circuit will allow you to measure resonant frequencies from kilohertz to over 10 megahertz... [Circuit by David Johnson P.E., 6/09/00]

LED Strings Powered by AC Line -  This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line.… [Designed by Ken Schultz, drawn by Dave Johnson 12.18.2004]

Level-Shifts AC Signals -  10-Jul-03 EDN Design Idea   AC signals can emanate from many sources, and many of these sources are incompatible with the most popular interface voltages, such as TTL. A temptation always exists to capacitively couple the ac signals because capacitive couplin… [by Ron Mancini, Texas Instruments, Bushnell, FL]

Line Input for Zoom H2 -  NOTE: Must register on this site… [Published in Elecktor July/Augu, 2010]

Line Powered High Intensity LED Flasher -  There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with... [Hobby Circuit designed by Dave Johnson P.E., 12/07/08]

Line Powered White LED Array -  There has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed... [Circuit by David A. Johnson P.E., 2/28/10]

Low Voltage 120vac Power Line Alarm -  This circuit will turn on a beeper when the line voltage drops below 100 volt AC.... [Circuit by Dave Johnson P.E., 7/09/06]

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 produce... [Circuit by David Johnson P.E., 6/09/00]

Power Amp-Single Polarity Power Supply-Using Model 423  -  No description, just schematic - OpAmps Lab Inc is the manufactor ofAmplifiers (Video / Audio / Distribution / Microphone / Equalization / Line / VCA / Power), Switchers (Routing / Assign / Matrix), Mult (Press) (Network-Feed) Boxes, Audio Transformers, Oscillators, Power-Supplies, Custom Sub-Systems. … [Application OpAmps Lab Inc.]

Pushbutton Controlled Up/Down Ramping Light -  There are times when you want a lamp to gradually change from dark to light and from light to dark, with each push of a pushbutton switch.  The circuit below performs this control function using a flip/flop and a classic pulse width modulation or PWM... [Circuit by David Johnson P.E., 3/22/09]

Reduced Power Sequential LED Flasher -  The 74HC4017 is a neat decade counter which has 10 decoded outputs.  When supplied with a low frequency clock and with a LED attached to each of the outputs, an interesting ten step sequential flasher effect can be produced.  The LEDs can be configured in... [Circuit by David Johnson P.E., 11/30/08]

Servo-Constant-Current Drive Amplifier-Using Model 440C  -  No description, just schematic - OpAmps Lab Inc is the manufactor ofAmplifiers (Video / Audio / Distribution / Microphone / Equalization / Line / VCA / Power), Switchers (Routing / Assign / Matrix), Mult (Press) (Network-Feed) Boxes, Audio Transformers, Oscillators, Power-Supplies, Custom Sub-Systems. … [Application OpAmps Lab Inc.]

Servo-Position-Using Model 423  -  No description, just schematic - OpAmps Lab Inc is the manufactor ofAmplifiers (Video / Audio / Distribution / Microphone / Equalization / Line / VCA / Power), Switchers (Routing / Assign / Matrix), Mult (Press) (Network-Feed) Boxes, Audio Transformers, Oscillators, Power-Supplies, Custom Sub-Systems. … [Application OpAmps Lab Inc.]

Servo-Velocity-Using Model 423  -  No description, just schematic - OpAmps Lab Inc is the manufactor ofAmplifiers (Video / Audio / Distribution / Microphone / Equalization / Line / VCA / Power), Switchers (Routing / Assign / Matrix), Mult (Press) (Network-Feed) Boxes, Audio Transformers, Oscillators, Power-Supplies, Custom Sub-Systems. … [Application OpAmps Lab Inc.]

Solid State Relay Requires Only 50ua Drive Current -  This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR... [Circuit by David Johnson P.E., 6/03/00]

SSR Requires Ultra Low Control Current -  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... [Hobby Circuit designed by David Johnson P.E., 6/03/00]

Under/Over Voltage Alarm on AC Line -  Power lines, which deviate much beyond normal voltages can damage expensive electronic equipment.  The 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... [Circuit by David Johnson P.E., 3/29/09]

Use An Integrator Instead of Coupling Capacitors -  02/16/12  EDN Design Idea   Level-shift a signal with an unknown dc offset to a known offset without ac coupling. An ultrasonic sensor circuit requiring self-adjustment to the level of an ac-input signal also must accommodate the signal’s unknown and variable dc-bias voltage. The circuit cannot use an ac coupling capacitor, and the resulting output must be level-shifted to a known dc offset. The design uses a dc-offset compensator (Figure 1).… [by Vladimir Rentyuk, Modul-98 Ltd, Zaporozhye, Ukraine]

Voltage Limiting sith a Supercapacitor -  Supercapacitors are working their way into more and more applications where electrical energy needs to be stored.  These robust devices can be charged and discharged 1000s of times and will typically outlast a battery... [Hobby Circuit designed by Dave Johnson P.E., 3/27/10]

Why Limit Your Power Supply's Input Range? -  03/20/03  EDN Design Idea   Multilayer capacitor doubles as varactor-Taking only a cursory look at the input-voltage ratings of your power-supply IC can limit the usable input-voltage range. With careful examination of an IC's operating specifications and cir… [by Michael Day, Texas Instruments, Dallas, TX]

AC Power Control Circuits



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