help required with regulator circuit please

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Raj1

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Joined 2003
#1
Hi,

I would like to use a low noise regulator circuit to provide a cleaner supply than standard regulators, I have with the help of a few members found 2 ciruicts that may be useful. The regulators will be used for 2 dacs, that will draw more current than the low power versions of the finnesse circuit provide....


With each circuit though there are a couple of issues that I need answers/help.

The first is the wenzel finnesse circuit
http://www.wenzel.com/graphics/cleanup2.gif

1) Can this circuit be adjusted to run off +8v input? V out +5v required.

2) Can someone please tell me what component values must be changed in order to get the +5v ouput, I can build stuff but haven't got a clue when it comes to working out required values, so I need help please!

3) Is there a very easily obtanable slot in alternative to mpsd54?


The second circuit which is technically more suitable is awkward as the design uses smt parts, so again if there are commonly available thru-hole alternatives please tell me (also would need component values for resistors etc).

http://dbserv.maxim-ic.com/appnotes.cfm?appnote_number=169

I have looked at some of the pcb's avaiable for these types of regulators, but this becomes pricey when you need a few of them. So I'd rather build them if possible (I need at least three). I'm quite suprised that nobody on the forum has organised a group buy for forum members where we could all buy pcb's at cost and on a non profit basis. This way a small pcb could be made up for replacing commonly found regulators in audio components. Trouble is I can't do pcb design, but I would be willing to handle shipping to others, if someone can put in a small pcb design for forum members. I'm sure there must be some kind of desire for this, judging by the amount of members that tweak components..............

Anyone interested in doing this??
Thanks
Raja
 
#2
Here's a link to the specs for the fmmt619

http://www.zetex.co.uk/3.0/b1-6.asp

can anyone suggest an alternative?

I can get the opamps as samples from maxim, they are available in a dil package. The transistor is a bit more difficult, firstly being an smt device and also hard to obtain in the UK in small quantities. Is there anything at all I can substitue easily in it's place?

Thanks
Raja
 
#5
 
#6
How much current do you need? And why isn't the standard 3-pin regulator like LM7805 good enough?

Your first circuit is a shunt regulator without a reference. Not very accurate, and very inefficient.

The second is a series regulator with a PNP pass transistor and an opamp as an error amplifier. Also with no reference.

The standard power supply chip LM723 would do that much better, with NPN output devices, integral reference and adjustable current limit. The DIP package will do 150 ma without external transistors. If you bypass the reference pin with a 0.1uF cap you can get ripple and noise down to a few millivolts.

The PDF has application circuits:

http://www.national.com/pf/LM/LM723.html
 
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