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Silicon Controlled Rectifier (SCR) Circuits
SCRs:   #'s -A      B - K      L - Q      R - Z


Last Updated: October 24, 2017 05:16 PM

Circuits Designed by Dave Johnson, P.E. :

Laser Light Detyector-10Mhz to 20Mhz -  This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system.  it has good ambient light immunity . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

LED Array powered by 24 VAC -  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 David A. Johnson P.E.-December, 2009

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 Dave Johnson P.E.-June, 2005

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 . . . Hobby Circuit designed by Dave Johnson P.E.-March, 1999

Low Power AC to DC Power Supply -  When you need some DC power fully isolated from the AC power line, this circuit may be just the ticket.  The circuit uses an inexpensive tiny off-the-shelf 6.8mH common mode filter coil from with a split bobbin as a high frequency transformer.  The circuit routes short 130v pulses to the primary winding of the coil every half cycle of the 60Hz line frequency.  it uses a silicon bilateral voltage triggered switch called a “sidac” to discharge a 0.1uF high voltage capacitor. . . Circuit by Dave Johnson P.E.-November, 2011

Minature 24VAC 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.. . . Circuit by David Johnson P.E.-July, 2009

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.-June, 2000

Monitors AC Current -  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 David A. Johnson P.E.-July, 2006

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
6 Models Available - Call 806-368-7747


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

Lamp Dimmer Full Wave SCR (120 Volt AC) -  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.    __ Designed by Bill Bowden

Laser Light Detyector-10Mhz to 20Mhz -  This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system.  it has good ambient light immunity . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

LASER Power Supply -  if you have ever worked with lasers, you know how fun and interesting it can be, you also know how expensive it can be.  The high voltage power supplies for the laser tubes are often more expensive then the tubes themselves.  This supply can be built with commmon parts, most of which you probably already have in your junk box.  The secret is the transformer used.  it is a common 9V 1A unit, connected backwards for step up __ Designed by Aaron Cake

Lead Acid Battery Charger with Float -  The circuit furnishes an initial charge voltage of 2.5 Volt-per-cell at 25°C to rapidly charge a Lead-Acid battery.  The charging current decreases as the battery charges, and when the current drops to about 180mA, the charging circuit reduces the output voltage to 2.35 Volt-per-cell, floating the battery in a fully charged state.  This lower voltage prevents the battery from overcharging, which would shorten its life.  The LM301A (Tony van Roon's U3) compares the voltage drop across R1 with an 18-mV reference set by R2.  The comparator's output controls the voltage regulator, forcing it to produce the lower float voltage when the battery-charging current passing __ Designed by Tony van Roon  VA3AVR

Lead/acid battery charger -  YES! ! ! !  Found the perfect solution for hum caused by filaments. But what happens after a few hours when the batteries start getting drained?  The logical follow-up of battery heated filaments is of course a battery charger.  The circuit below I got from a friend who used them in his own 26 preamp (nice tube, eh! ?).  it is very simple to build requiring only a handful of cheap parts and an extra winding on your power tranny (or a separate tranny).  Since the charger described is not active during sound reproduction, I have made no criteria on parts quality, so el-cheapo was the way to go. __ Contact site @ vt52 . com

Lead-Acid Battery Monitor -  This mini-project came about from building a garden shed.  I decided to re-purpose an old UPS battery along with some spare halogen downlighters for illumination.  But as I researched lead-acid technology, I decided that I needed something rather more sophisticated than a simple switch if I wanted the batteries to survive __ Designed by Mark Hennessy

LED Array powered by 24 VAC -  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 David A. Johnson P.E.-December, 2009

LED Power Supply Has Battery Backup -  04/08/10 EDN Design Ideas:  Power three to six LEDs from an ac- or dc-power source and charge a backup battery.   __ Circuit Design by Zhihong Yu, Juno Lighting Group, Des Plaines, IL

Light Controller High Side -  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

Line Power Supply -  This circuit provides a regulated output without a power transformer.  it is similar to common circuits, except that a zener diode is replaced with an SCR.    This is far more robust against line voltages surges than a zener diode version, plus there is no h __ Designed by Andrew R. Morris

Linear Power Supply 8 ..16 V ~ 10A that offers low noise -  The Mains Voltage (230 V) is transformed down to 15 V with a 150 W Transformer from Farnell. (#1675077, MULTIC OMP VTX-146-160-115).  Rectification is done by a GBPC2510, (Farnell, #1621698).  Afterwards, a bank of 11 Capacitors of 2200 µF, 35 V smoothes the rectified ac voltage. __ Designed by Alexander C. Frank, aka Ajarn Changpuak

Linear regulated bench power supply 20V, 2A-easy to upgrade -  This Power Supply was designed as an advanced Project to get used to soldering - and - at the end - have something useful. __ Designed by Alexander C. Frank, aka Ajarn Changpuak

Linear regulator=low-cost DC/DC converter -  03/16/95 EDN Design Ideas:  A linear regulator is often a better choice for developing supply voltages below 3.3 V than a switching regulator.  At low output voltages and moderate currents, the linear regulator is less expensive and requires less pc-board are __ Circuit Design by Susanne Nell, Breitenfurt, Austria

linear voltage regulator with ultra Low drop -  The circuit is a MOSFET based linear voltage regulator with a voltage drop of as low as 60 mV at 1 ampere.  Drop of a fewer millivolts is possible with better MOSFETs having lower RDS (on) resistance.  The circuit in Fig.1 uses 15V-0-15V secondary __ Designed by Radio LocMan

Lithium Ion Battery Charger -  PIC  Project  Lithium ion batteries pack a lot of power by weight compared to other types.  There are 2 things that need to be handled differently than NIC ad on NiMH
: __ Designed by Luhan Monat-Mesa Arizona

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 Dave Johnson P.E.-June, 2005

LM3914 battery Monitor -  This circuit should be powered by its own battery, otherwise you might get an innacurate reading.  hook the to-be-monitored battery to pin 5 of the chip.   __ Designed by Andy Wilson

Low Cost Universal Battery Charger -  This is a Low Cost Universal Battery Charger Circuit.  This circuit is used to charge NIC D-NiMH
batteries and ideal for car use.  This circuit transforms a mains adapter to a charger.  it can be used to charge MP3 players, portables, toys cellular phone, video batteries.__ 

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 . . . Hobby Circuit designed by Dave Johnson P.E.-March, 1999

Low Power 12v Transformerless Power Supply -  Many circuits can be powered directly from the mains with the aid of a series capacitor (C1).  The disadvantage of this approach is that usually only one half cycle of the mains wave-form can be used to produce a DC voltage.  An obvious solution is to use a bridge rectifier to perform full-wave rectification, which__ 

Low Power AC to DC Power Supply -  When you need some DC power fully isolated from the AC power line, this circuit may be just the ticket.  The circuit uses an inexpensive tiny off-the-shelf 6.8mH common mode filter coil from with a split bobbin as a high frequency transformer.  The circuit routes short 130v pulses to the primary winding of the coil every half cycle of the 60Hz line frequency.  it uses a silicon bilateral voltage triggered switch called a “sidac” to discharge a 0.1uF high voltage capacitor. . . Circuit by Dave Johnson P.E.-November, 2011

Low Power LED Voltmeter -  This is a low power voltmeter circuit that can be used with alternative energy systems that run on 12 and 24 volt batteries.  The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries and over the 22 to 32 volt __ Designed by G. Forrest Cook

Low side 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

Low Voltage Power Supply / Step Down using a MC34063 -  A step-down converter calculator with examples.  To escort the "High Voltage Power Supply with the MC34063" which was developped as a building block for e.g.  geiger counters.  This one is intended to supply anything digital, using a voltage like 3.3 V. __ Designed by Alexander C. Frank, aka Ajarn Changpuak

Magnetic Energy Storage & Switching Power Supplies -  An introduction to Switching Supply Design __ Designed by Craig Taylor

Minature 24VAC 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.. . . Circuit by David Johnson P.E.-July, 2009

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.-June, 2000

Monitors AC Current -  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 David A. Johnson P.E.-July, 2006

MOSFET switch provides efficient AC/DC conversion -  02/17/00 EDN Design Ideas:  Occasionally, you have access to a transformer for powering a dc circuit, but its output voltage is much higher than that required for the dc voltage.  The full-wave-rectified and filtered output of an ac input voltage V X , is V DC =1.414V X-2V F , where V F is the forward drop in the rectifier (approximately 0.7V).    __ Circuit Design by Spehro Pephany, Trexon Inc, Toronto, ON, Canada - February 17, 2000

MOSFET, Inverter 12 volt unit -  A Very Reliable, Efficient and Practical Design.  Do Not ask how to Build this for Power ratings over 1000 watts, That is NOT Practical.   __ Designed by G.L. Chemelec

Motor Accu Ladder -  Article is in Dutch __ Designed by Jan Hammer

Multiple voltage power supply -  Schematic only, no circuit description __ Designed by Andy Wilson

Multi-Purpose Inverter -  Permanent lash-up for driving anything.  Complete with over-current and temperature shutdown! __ 

NiCad Battery Charger -  This simple charger uses a single transistor as a constant current source.  The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor.  The base - emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. __ Contact IQ Technologies

NiCad Discharger for Tx & Rx Packs -  The reason I designed this discharger are many, however I will list a typical example.  A modeler charges his batteies for 14 hrs, then goes to the field for a fly.  He then rests for a week, then charges his batteries again for 14 hrs and flies again.  The third time, he repeats the procedure, then wonders why his aircraft has a major argument with the runway.  The problem with this method is that he is rechargeing a battey pack which after the first week, is in an unknown state of charge __ Designed by John Nooyen

Ni-Cd Batteries Charger -  Schematic + PCB + Parts List __ Contact IQ Technologies

Nine Volt Battery Eliminator -  for guitar pedals, radios etc __ Designed by G. Forrest Cook

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 Dave Johnson P.E.-December, 2009

Nine-Volt Stabilized Power Supply -  Schematic only __ Designed by Tony van Roon  VA3AVR

Non-Isolated Off-Line AC to DC Power Supply -  The design below does indeed fit within a one square inch circuit board area.  it can be used over a wide 24vac – 120vac input voltage.  The circuit gates only small slivers of the rectified AC signal to a 470uF energy storage capacitor.  The 180K and the 10K resistors define the peak voltage fed to the capacitor.  Other resistor values can be used to shift the DC output voltage up or down.  Remember, this circuit should only be used with DC circuits that can be connected directly to the power line.  Dangerous voltages exist everywhere.Circuit Solution by Dave Johnson P.E.-July, 2006

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SCRs:   #'s -A      B - K      L - Q      R - Z

 


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