Tuesday, May 15, 2012

The Power Transformer’s Ugly Stepsister - the Pulse Transformer

By definition, transformers convert AC power from one voltage to another.  For example, a typical step down transformer will take 480 volts to 220 or 110 volts for home use.  The laws of physics dictate that a transformer will not work with DC power.  If you ask a physicist why DC power will not work in a transformer, they will mumble something about quantum mechanics, electron spins and electron coupling and then quickly look down at their shoes until you walk away.

So if you accept that a transformer converts AC power then the wave form is a typical sinusoidal alternating current shape as shown below.   The frequency determines the number of peaks per second, and typical US AC power is 60 cycles per second.

Sometimes this smooth oscillating wave will not do what you want therefore you may need a square wave form.

Why would anyone prefer the odd and ugly boxy square wave form over the smooth eye-appealing sinusoidal shape?  The answer is usually that a nice square wave, that is a pulse, can be used in different ways than the “s” shaped curve.  A pulse is of great use in applications such as data communications or signaling a power semiconductor to turn on or off.    One of the practical applications of a pulse transformer is to produce high power pulses that feed into radar to produce the sound waves that prove I don’t understand that a 55 mile per hour speed limit does not mean 55 miles per hour give or take 20.

A pulse transformer thus has a different design than the typical power transformer.  (See pulse transformer operating principles)  The pulse transformer designer needs to be concerned about such issues as low coupling capacitance and excellent insulation properties to prevent high breakdown voltages.  Pulse transformer design can give a range of “square” shapes that can be actually rectangular with varying degrees of length and amplitude.   These variations allow for giving stronger or weaker pulses and vary the length of time of the pulse.

If you need a circuit to produce a signal that is not the typical analog signal then a pulse transformer may fit your needs quite nicely.  At Butler Winding, we manufacture custom pulse transformers just like the one mentioned above.  View additional Butler Winding pulse transformer projects.

Written by Denny Wist
President of Butler Winding