🚀 go-pugleaf

In article <1340@bgsuvax.UUCP>, hovan@bgsuvax.UUCP (John Hovan) writes:
> 
> 
> 
> 	While working with various high quality electronic components, I have
> noticed the utilization of switching power supplies.  I know these supplies
> dissipate less heat and work by somehow increasing the input frequency,
> but are these supplies considered new technology to replace humming          
> transformers?  More importantly can anyone take the time to explain the theory
> behind how these supplies actually work, and why they are used rather than    
> the traditional transformer/diode bridge type?

The switching power supply has been developed in response to demand for
lightweight, efficient & regulated power supplies.  Transformer core
size is related to the operating frequency due to their saturation
characteristics.  60Hz transformer cores are huge, with a lot of wire, 
and are heavy and lossy.  Linear regulators are also very lossy.  Switching
supplies operate in the frequency range of 20KHz to 1MHz with lightweight
cores, using pulse modulation techniques for efficient regulation.
Essentially switchers they work like this:

The ac line voltage is directly rectified and filtered to produce a raw dc.
This dc is fed to a switching element, ie., transistor, FET, SCR.
This device will chop the raw dc at the operating frequency resulting
in a high voltage chopped waveform.  This is waveform is fed to a 
transformer, rectified, and integrated to a smooth dc.  Regulation is
accomplished by monitoring the output voltage and varying the duty cycle
of the high voltage chopped waveform. (hence the term PWM, Pulse Width
Modulator).

An analogy might be to switch a light off and on very fast, so that one
can't see the switch cycles.  The thermal mass and the eye would be
the integrator, varying the duty cycle would control the intensity.

Many types of switchers exist:
Half and full bridge, push pull, Cuk,  flyback, series-resonant, 
forward converter, etc.

A good book is: High Frequency Switching Power Supplies,
George Chryssis, McGraw-Hill #ISBN 0-07-010949-4




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