W. James McKeefery
408 946-8550 fax 408 946-8552

Power Conversion and Control Engineer

Over 15 years as an Independent Consultant Specializing in Switch Mode power conversion circuitry and system design. My diverse background also includes combined analog, digital and Analog ASICs, consumer electronics, and toy product design.


Power Conversion and Control

Servo Systems, DC Motor Controls

Consumer Electronics design

Electromechanical Prototype Fabrication

High Volume Manufacturing Experience


Power Conversion Experience






Tropos Networks



Switching Power Supplies for telecom use.  Harsh environment, lightning strike, load dump immune

The first power converter was a wide input range, 90VAC to 560VAC supply with a 9V at 6A output.  I used a power factor correcting converter IC and distributed the 6:1 range equally between the primary PFC converter and the two transistor forward converter.  The efficiency was 85% to 90% and was designed to be very reliable.   The POE supply was a 20Watt high isolation fly back.  The vehicle power converter is designed for use in police cars, 8 to 34V in and 9V at 3.3A out.  The third supply was for police and emergency vehicles and had to take the vehicle load dump surge specification.  This design was a two transistor forward converter so I could use the transformer turns ratio to get the 9.0V output at 3.3A even though the input drops to 8V and may rise up to 34 Volts. 

Shoot The Moon

Power systems as an Inventor selling Ideas to Toy Companies

STM is my agent for selling these Ideas

Toy Projects of all types,  RC Rally for Fisher Price, with royalty agreement.  Very cheap  50 mw gate and discrete power converter.  Switching power converters for NMH battery chargers, patent for same.  Projects include:  Magnetic field direction finder,  Off line SCR and capacitive battery charger – no transformer,  FRS radio Home Base product,  Cody talking book prototype,  Doll house character location sensor – magnetic,  I  invented  the electric scooter in 1994 and Shoot The Moon  marketed to Hasbro for me. 


14 output switching power supply

This company makes a handheld ultrasonic imaging unit .  This was a 14 output power supply that occupied only 8 cubic inches.  From 1.8V for FPGA core  to 96V for the piezoelectric drivers.  A very complex design.  Innovative use of stacked supplies for the high voltage.  One of the high current converters used a 3 phase design to spread the switching edges over the 360 degrees and reduce stress on the filter components.  All of the supplies ran off of lithium batteries.

Trazar Corporation

Servo controllers for RF tank coils

This company make servo controllers for RF tank coils used in plasma generators for wafer fabrication .  I became their expert in servo control for  these products.  Dual servo controllers in the 10 Watt range, slow stability loops, all analog.   The control loop looked at the SWR of the RF circuit and fed that back to my controller to close the loop.

Guidant Co.

Power conversion over isolation barrier

Cardiac stint project.  They needed to couple power over an isolation barrier with full 360 degree plus of mechanical  rotation  range.  I helped analyze possible methods.  The magnetic transformer coupling was preferred.

Gyricon Media Inc,
Xerox Park




High voltage low power converters

I developed high voltage low power converters for Xerox’s “Electronic Paper” that could run for long periods of time from lithium batteries.  The output voltage was variable up to 120 VDC.  The input supply was 2 to 3 volts.  They did not want to have custom transformers made so I designed one of the first planar transformers in the US.  The multilayer PCB became the transformer windings and only the ferrite E-I core needed to be cemented in production.  Several designs were done and all were successful, but the electronic paper was not. 

Immersion Corp.

Four quadrant PWM motor control for Force feedback

Force feedback Joysticks and steering wheels.  I used a four quadrant PWM motor control method that eliminated hysteresus through the zero point.  Many different modules were developed, from 10 watts to 200 watts.  Torque was the main feedback element.  This was accomplished by accurately controlling the motor current.  These were used in medical applications and Logitek products such as the racing steering wheels and force feedback joysticks.


Magnetic field positioning system.

This was a Gun Positioning system for arcade video game.   Multiple ideas were brainstormed and  proposed.  A magnetic field radiating and receiving system was prototyped and integrated with one of their games.  The ability to play shooting game without a tether was valuable.

OnPrem Networks

Power system for dual redundancy

This company makes a telecommunications box that needs to have (2) 60W switching power supplies that run in dual redundant mode.  I designed the power section of the mother board that accepted the 2 supplies output and allowed hot swap redundancy.


Mill Motor Controller

This was a 1.5 HP 90VDC motor controller  with speed, current, and direction controlled buy opto couplers. The mill cut custom insoles for athletic footwear such as ski boots.  The motor was driven by an “H” bridge of High Power MOSFETs  with isolated high side FET drivers.  The PCB layout was critical and I was directly involved with the layout design.  Stability over all load and speed conditions as well as reversing and back EMF was achieved.

Softbook Press

Multiple switching power supply system for a laptop computer.

The Softbook was an electronic book halfway between a PDA and a Laptop.  I designed all of the power converters (4) and Lithium Ion battery chargers needed for a laptop like power environment.  This design had very high efficiency and reliability.  I also researched and designed our own cold cathode fluorescent back light converter that was superior to available designs.  

Power Up Products

Electronic circuit breaker using power MOSFETs

This was an electronic circuit breaker using power MOSFETs for use in emergency vehicles. The existing circuit breaker technology was not reliable enough for ambulances and fire trucks.  They needed multiple modules for all currents and a new breaker panel designed.  I used the PCB traces to measure current and then measured the trace temperature with a thermistor to compensate for the copper’s positive temperature coefficient.

Unistar Technology

Electronic Sun Visor  Servo Controller

This is the electronic sun visor project.  The first proto was mainly R&D.  The second got us in the door in Detroit.  I designed all of the circuitry and wrote the code for a PIC microprocessor.  A servo controlled “flag” covering each eye protected the driver from the sun without obstructing his vision. Very compact and quiet.  I did much of the mechanical design as well.

Stryker Eddoscopy

Regulated 500W Halogen light source for endoscopic surgery

The amount of light that was sent down the fiber optic cable was regulated by a circular aperature slit in a rotating disk.  The video signal white level was detected and fed back to a servo that rotated the disk to regulate the illumination of the surgical area.  I designed both the mechanical and electronic portions of this design.  Removing stepper motor flicker from the video picture was a challenge.

Playskool Technology Group

Animation products using low power servo systems

I developed a full custom analog IC for their animated toy product line.  The IC was mounted COB and that small daughter board was mounted edgewise into the main board.  Component count was minimized  as much as possible.  I followed the design to high volume manufacture, 500,000 pieces,  in Hong Kong and mainland China.  I was involved in the mechanics of the servo design as well as the injection moulding tooling.

Worlds of Wonder Inc.

Power systems as part of my job designing Toy Products

Several projects used NiCad and NMH battery chargers with thermal and slope cutoff.   Many products used audio power amplifiers.  A slot less car racing set used magnetic fields to automatically navigate several race cars around a rubberized track.  Worlds of Wonder was

the first company to bring true high technology to children's products.  As one of the first engineers, I was involved in the creation of "Teddy Ruxpin" the first servo controlled from cassette tape animated talking teddy bear.   I had total design responsibility for this and eight other animated products.  Several of these used  an absolute position digital servo of my own design.


Electroluminescent Panel Power Converter

Electroluminescent Panel Power Converter for lap top computer.  Converted 5Vdc  to 300Vp-p 500HZ Sine wave.   The  15 Watt peak power was converted to the panel, and then  back to the 5V supply for each cycle of the 500 HZ. For the same light output, this method required 1/4 of the power. Module size 4.5" by .75" by 0.2" thick,  25 Watts per cubic inch.  All surface mount technology with a 0.020 thick PCB.


Cromemco Inc.

Computer system power supplies

I designed power supplies which ranged from 25 to 450 watts for a series of S-100 bus microcomputer systems for engineering and graphics applications.   I designed a 300W Off Line Switcher with 6 Outputs and  redundant operation without the use of steering diodes.  Automatic line voltage selection circuitry.  Power density of 2.5 watts per cubic inch.  Coupled output inductors for improved cross regulation.   I designed a Battery Back-up system for their Personal Computer. It used a 12V input 250 VDC output,  50 KHZ bipolar fly back  converter  with  Zero transition time.  It had TTL status output  and had a 50 watt load capacity .  The  batteries were fully  isolated.  

Transistor Devices Inc.

Military spec Power Supplies

Electronic Active Loads

Design engineer of custom power supplies and power control equipment to military and commercial specifications.  I designed both linear and switch mode supplies that were designed to high reliability standards.  I did many MTBF studies and that  illuminated for me what components are the least reliable and should be avoided in the design phase.   

I was the chief engineer in charge of their Active Loads that were used for  power supply, battery testing. This product line had 12 different models and  was sold to commercial customers  Power range of 100 to 3000W and up to 300 amps. One custom unit for the Air Force was 2500 amps and could dissipate 25 KW. Most of these designs were remotely programmable for computerized test stations. These units were designed for very high durability and reliability.