
Power supplies 263
critical sort of load, an inverter with a sine wave
output is used. Many of these still use square wave
switching, but with an output transformer tuned to
resonance at the output frequency of 50 or 60 Hz.
The 'elastic' used to accommodate the varying
instantaneous voltage difference between a sine
wave and a square wave is often a separate
inductor, or sometimes a transformer design with a
deliberately high leakage inductance between pri-
mary and secondary (output) winding. The effici-
ency at full load is usually not quite so high as
square wave output types, but the waveform is
very fair at 5% distortion or less.
Frequency ...