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Three Terminal Regulators - 7905, 7508 and 7512.

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I'm working on the power supply of my radio receiver project and looking at the 78xx series three terminal regulators in the TO-220 package. 

Any ideas on which ones work the best?  I want to keep the power input fairly clean.  Bought a Hammond transformer to take the 110-120v input from the computer type connector (IEC 60320-1 Type C13).  Found a bunch of Nichicon electrolytic caps, I'll use. 

The supply has to turn a bi-color LED from red into green when the unit is turned on (or comes from standby power).  I also bought a white/blue one for posterity. :-)



--- Quote from: gbowne1 on July 03, 2011, 06:23:00 am ---Any ideas on which ones work the best?
--- End quote ---

Here we go again. There is no such thing as "the best". You don't need the afreaking best, you need good enough.

If you are really concerned about your power supply you are putting the cart before the horse with your search for "the best". Quantify how good the power needs to be for your circuit. Then you know how bad the power supply can be allowed to be (with a certain margin to stay on the safe side). Then check potential power supply candidates (of which the regulators are only a part) if they are good enough.

If all you want to drive is an led then they will be fine, but I suspect you really want to do a little more perhaps power the device? In which case we need more info before we can make a judgement ;D


--- Quote from: gbowne1 on July 03, 2011, 06:23:00 am ---I want to keep the power input fairly clean.


--- End quote ---

Greg did you made the wild thought to set those three in line as triple filtering ?

The 78XX series are all pretty much the same, it is just a question of what voltage you need/want.  The 317 adjustable regulators have slightly better specs, especially if you add a bypass capacitor to the adjust pin, but the difference is unimportant in most cases: you pick the 317 because you need adjustable voltage.

At high frequency, none of the standard regulators do much at all.  They provide neither particularly good regulation, nor very good supply rejection.  At the high frequency, you are really depending on your input/output filters to provide the performance you need.  For instance, low ESR capacitors are key to providing good load regulation -- but watch out for stability if you switch to a LDO regulator.

However, what you need, or what is best for your application depends on your actual requirements.

--- Quote from: Kiriakos-GR ---Greg did you made the wild thought to set those three in line as triple filtering ?

--- End quote ---

I wouldn't recommend this, I expect the performance will be less than if you implement multi-stage RC filtering, but the idea is right.  It is hard to get tremendous rejection in a single stage, cascading filters generally improves your performance much more than building a single super-awesome filter. The reason I don't suggest chaining multiple 78XX regulators is that they are mostly all good at DC where it is easy to get really high supply rejection in a single stage.  Passive filters and capacitance multipliers are much better at high frequency.


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