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Power Supplies / Converters: AC to AC
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Power Supplies -- Main Page

Last Updated: January 01, 2018 04:03 AM

Circuits Designed by Dave Johnson, P.E. :

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 for the140vac range and in series for the 280vac range. The selector switch also diverts power to the appropriate output socket to avoid mishaps in sending the wrong voltage to the load. My home-built unit also included an AC volt and Amp meter to monitor the output. However, this circuit only indicates the AC power connections.

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

Line Output / Flyback transformer tester  -  This is a 'ringer'-type tester I (Bob Barker) originally designed for in-circuit testing of Line Output (Flyback) transformers in TVs and computer monitors.  After a couple of technician-years of evaluation in actual servicing situations, it's also proved to be heLPFul in locating shorted diodes, capacitors and deflection yokes in horizontal deflection stages.  LOPT/FBT condition is shown on an 8 LED 'bargraph' display.   __ Designed by Bobarker, not the TV Host

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 David Johnson P.E.-March 27, 1999

Low-cost switcher converts 5 to 24V  -  02/16/98 EDN Design Ideas:  (File contains several circuits, scroll to find this one)  __ Circuit Design by Paul C Florian, Plano, TX

Method sets voltage in multiple-output converters  -  02/01/01 EDN Design Ideas:  When you design a transformer for any power converter, you face several compromises.  You must trade off core size against the number of primary turns and flux density.  Another trade-off is the number of turns and winding resistance versus the associated losses.  After making these trade-offs, you usually arrive at a good compromise that involves the primary and secondary turns.  However, if the converter has more than one output, you face a new set of compromises.   __ Circuit Design by Robert Bell, On Semiconductor, Phoenix, AZ

Mixed Feedback Drive  for Audio Output Transformers  -  Using feedback eliminates transformer distortion and primary resistance__ 

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 Johnson P.E.-July 10, 2006

Novel controls AC power  -  01/07/99 EDN Design Ideas:  (Several Circuits in File.  Scroll to find this one) The simple and inexpensive power-control circuit in Figure 1 uses a readily available fan regulator with built-in phase control.  Such fan regulators are limited to approximately 100W.  The circuit in Figure 1 adds two SCRs and a few components   Page includes several designs.   __ Circuit Design by Narendra Paranjape, Tata Chemicals Ltd, Mithapur, India

Parasitic Capacitance Effects in Step-Up Transformer Design  -  AN39 Linear Technology This note explores the causes of the large resonating current spikes on the leading edge of the switch current waveform.  These anomalies are exacerbated in very high voltage designs.  __ Linear Technology/Analog Devices

Plus & Minus DC Power Supply  -  This is a classic example of a regulated DC power supply that produces both a positive 15v and a negative 15v from a 20vac wall adapter . . . Hobby Circuit designed by David A. Johnson P.E.-December 13, 2004

Power Amp using a TDA2003  -  Here is the circuit diagram of a 10W audio amplifier using the popular TDA2003 IC from SGS Thomson.  The IC can easily deliver 10W to a 4 Ohms load at 18V DC supply voltage.  The IC can be also operated from 12V and that makes it applicable in car audio systems__ 

Power Supplies & Regulators  -  includes several designs, scroll down.  new low power discrete switcher __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

RS-232 Serial Interface Status Indicator Circuit  -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights . . . Hobby Circuit designed by David A. Johnson P.E.-December 15, 2004

Signal transformer application  -  Coilcraft RF Magnetics App Note- __ Designed by Coilcraft Power Magnetics Application Note

Simple Circuit algorithm transforms filter coefficients  -  01/21/99 EDN Design Ideas:  To synthesize infinite-impulse-response (iiR]-filter functions, expressed as H (z], you commonly use analog prototype-filter functions, expressed as H (s], using the bilinear-z transform.  This operation entails some algebraic complexity in calculating the filter coefficients.  The simple algorithm shown here transforms the prototype-filter coefficients (W0, W1, W2]to the iiR digital-filter coefficients (U0, U1, U2].  These coefficients transform from   Page includes several designs.  Scroll to find this one __ Circuit Design by Frank Vitaljic, Bellingham, WA

Simple Circuit Switching Regulator  -    NOTE: Scroll down - When batteries are used to power lower voltage circuits, a switching regulator is desirable to conserve battery life. There are excellent ICs  that can do the job with great efficiency and small size. An example is the Maxim (www.maximic.com) MAX639 which converts inputs from 5.5 to 11.5 volts to 5 volts at up to 225mA.  The only additional parts are an inductor, schottky rectifier and a couple of capacitors. The following circuit is a discrete switcher similar in power handling capability to the MAX639. __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Step Down Rectifier Makes a Simple Circuit DC Power Supply  -  04/09/98 EDN-Design Feature (Several circuits included.  Scrol to find this one) A simple and useful nonisolated rectifier features voltage step-down operation, acceptable Class A line-current harmonics, inherent short-circuit protection, and, optionally __ Circuit Design by Nathan O Sokal, Design Automation Inc, K Kit Sum, Consultant, and David C Hamill, Surrey Space Centre

Telephone Ring Generator using 60hz Power Transformer  -  This ring generator will ring a telephone once every 10 seconds.  The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor.  The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer __ Designed by Bill Bowden

Tester 4-20ma Current Loop  -  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 . . . Hobby Circuit designed by David Johnson P.E.-November 02, 2004

Three-Terminal Adjustable Regulators  -    NOTE: Scroll down - The unregulated DC supply is a very common type and the simple regulator shown in fig. 1 may be added for projects that require a stable voltage. __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Transformer Buys Lower Shutdown Current  -  11/23/94 EDN Design Ideas:  The step-up DC/DC converter in Fig 1 trades a slight loss in efficiency and a transformer in place of a less expensive inductor for two important advantages  The inductor offers low shutdown current because the transformer eliminates a leakage path.  The circuit stays in regulation, even __ Circuit Design by Terry Millward, Maxim Integrated Products, Reading, UK

Transformer Coupled Splitter  -  Active amplified transformer isolated signal splitter that enables hum-free connection of1-guitar to more than1-amp as well as having a direct output __ Designed by Guitar Effect RC Keen

Transformer driver controls bidirectional switch  -  07/17/97 EDN Design Ideas:  You can use a transformer-driver IC to simply control a MOSFET on/off switch __ Circuit Design by Gerald Grady, Maxim Integrated Products, Sunnyvale, CA

Transformerless Power Supply  -  I have received a few emails asking for a transformerless power supply.  Here is such a supply.  This supply uses no heavy step down transformer and has an extremely low parts count.  The circuit can be built very small and can supply small currents for small projects.  The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents __ Designed by Aaron Cake

Transformerless Power Supply  -  I have had several requests for a power supply project without using a power supply. This can save the expense of buying a transformer, but presents potentially lethal voltages at the output terminals.Under no circumstances should a beginner attempt to build such a project. Please also read the Disclaimer on this site. __ Designed by Ron J

Transformerless Power Supply  -  Power Supply Circuits:  This circuit will supply up to about 20mA at 12 volts.  It uses capacitive reactance instead of resistance - so it doesn't generate very much heat.  The circuit was designed to provide a cheap, compact power supply for CMOS logic circuits that require only a few milliamps.  The logic circuits were then used to control mains equipment, using an optically-isolated TRIAC. __ Designed by Ron J.

Transformerless Power Supply (jose pino)  -  Simple, low cost and easy to build power supply.  Ideal for applications that doesn't require too much power. (5/28/2006)  __ Designed by Jose Pino

Use Amplifier Phono Input as Line Level Input: Inverse RIAA Filter  -  The circuit does two functions: signal level attenuation and inverse RiAA filtering.  The signal attenuation is needed to convert the 500 mV signal to 2.5 mV signal.  The inverse-RiAA filtering is needed to make the frequency response of the system flat (same equalization that is used when music is transferred to vinyl in the studio).  The picture __ Designed by Tomi Engdahl

Variable AC Power Supply  -  in electronics, it is often handy to have a fully isolated variable AC power supply.  With such a device you can safely test various AC powered circuits and even probe around in the circuit with an oscilloscope.  The hobby circuit below was designed to . . . Hobby Circuit designed by Dave Johnson P.E.-July 08, 2000

Voltage Boost to Series Regulator provided by Capacitor  -  This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range.  It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall power adapter power supply . . . Hobby Circuit designed by Dave Johnson P.E.-December 24, 1998

Got Designs?
Please eMail
if you want me to link to and/or post your original design Thanks.

            Power Supplies / Converters: AC to AC:   #'s - K      L - Z 
Power Supplies -- Main Page

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