Power Supplies - Of The Bench Variety...

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Re: Power Supplies - Of The Bench Variety...

Postby Steve Anderson » Sun Nov 06, 2022 12:37 pm

Variable capacitors are a rare sight these days, especially those rated for high voltages and currents, e.g. those used in transmitters. The next item on the endangered species list may be the humble power transformer. Compared to a cheap switched-mode device they're large, heavy, expensive (all that copper and steel), produce heat and have large AC magnetic fields. Toroidal versions are better in virtually all respects except price, watt-for-watt they are more expensive. Plus all transformers need rectifiers and large smoothing caps to produce DC, and electronic regulation (if needed).

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Re: Power Supplies - Of The Bench Variety...

Postby Steve Anderson » Tue Nov 08, 2022 6:14 pm

Klaas, I'll take your original sentence and modify it slightly...changes in blue..."Supply voltages should never have to be more precise than +/- 0.5 volt. If your application doesn't work at that voltage, something else is faulty."...maybe not faulty, but a poor design.

Now, there is a historical exception to this - the original TTL (74xx series) which was specified from 4.75V to 5.25V. Later versions (74HCxxx for example) quite happily operate from 2-6V, though as expected at lower voltages the speed is limited. That depends on the application.

More often that not, using a regulator in a power supply isn't so much a voltage sensitivity/accuracy issue, but of hum/ripple elimination. Often adding a regulator which should mop-up any residual ripple in the power supply is cheaper and smaller than a larger capacitor. The regulation it provides is a bonus, most often it isn't required.

However the ripple rejection of most op-amps (delving into the analogue world here) is so high these days even that is a moot point. As ever, it depends on the application. You wouldn't want a volt of ripple on the supply for a microphone pre-amp for example. A 40W power amp, no issue.

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