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Inverting regulator (-ve rail from +ve supply) - current requirements?
Inverting regulator (-ve rail from +ve supply) - current requirements?
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Old 5th October 2010, 07:42 PM   #1
peskywinnets is offline peskywinnets  United Kingdom
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Default Inverting regulator (-ve rail from +ve supply) - current requirements?

Rather than go the single supply/ 'virtual' ground way of things, I'm making up a little circuit with a TL072 preamp & I'd like to go with dual rails. Because of space constraints, I only want to feed the overall circuit wiith 9V ...from this I will regulate down to +5v. So I need an inverting regulator....which will give me -5V from that

A quick check & it seems all the low priced inverting regulators have somewhat low current delivery ability (10-15mA)...so to my line of questioning.

How much current do you think the negative rail of a typical dual supply TL072 preampifier amplifier will pull? (using non-inverting ->non inverting stages)

10mA, 15mA, more?

Last edited by peskywinnets; 5th October 2010 at 07:51 PM.
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Old 5th October 2010, 08:59 PM   #2
BobEllis is offline BobEllis  United States
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The data sheet is your friend - http://focus.ti.com/lit/ds/symlink/tl072.pdf look for Icc on page 8, you'll see that 10 mA supply is plenty.

What may not be plenty is your rail voltage - take a look at the output swing @15V rails, it looks like you'll only be able to swing 2V on 5V rails (or less if your load is under 10K). Is that enough for your application? Not a lot of headroom. Higher rails or a rail to rail op amp may be more appropriate.
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Old 5th October 2010, 09:25 PM   #3
boyofwax is offline boyofwax  Netherlands
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The TL082 in my preamp draws 3.6 mA @ 2x15v.
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Old 5th October 2010, 11:05 PM   #4
wakibaki is offline wakibaki  United Kingdom
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EXAR|SP6661EN-L|CHARGE PUMP INVERTER 200MA, 6661 | Farnell United Kingdom

This'll give you a -5V rail @ 200mA

And here's a -9V one:

http://www.geofex.com/circuits/+9_to_-9.htm

w

Last edited by wakibaki; 5th October 2010 at 11:09 PM.
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Old 6th October 2010, 01:59 PM   #5
peskywinnets is offline peskywinnets  United Kingdom
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thanks guys - I suspected it was in single digits of mA draw, but it's nice to have it reaffirmed.

Wakibike, I'd rather keep the cost as low as possible (I might need a few), and by proxy that means using one with the least amount of current 'supply' I can get away with....I'm actually eyeing this one...

MICROCHIP|TCM829ECT713|CHARGE PUMP, CONV, SOT23A-5 | Farnell United Kingdom

I bit smaller than I like to work with, but not impossibly so.
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Old 6th October 2010, 03:26 PM   #6
macboy is offline macboy  Canada
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I have to ask, if you are using a 9V battery, and want +/- 5 V rails, why not just create a virtualy ground at 4.5 V, giving you +/- 4.5 V rails? You can use an opamp voltage follower to create a very low impedance virtual ground will very little wasted power (compared to just using a voltage divider).
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Old 6th October 2010, 07:26 PM   #7
peskywinnets is offline peskywinnets  United Kingdom
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Yes, I know. ..hammer to crack a nut - never built a dual rail & just fancied having a dabble - just educating myself & experimenting really.
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Old 7th October 2010, 12:34 PM   #8
macboy is offline macboy  Canada
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Quote:
Originally Posted by peskywinnets View Post
Yes, I know. ..hammer to crack a nut - never built a dual rail & just fancied having a dabble - just educating myself & experimenting really.
That's actually a perfectly good reason.
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Old 7th October 2010, 01:00 PM   #9
jackinnj is offline jackinnj  United States
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Inverting regulator (-ve rail from +ve supply) - current requirements?
You can use any number of SMPS chips to derive an inverted voltage -- I used the National Semi "Simple Switchers" followed by an LM337L, (allowing for the overhead of the linear regulator). Pete Millet also used a Murata DC-DC converter in his sound-card adapter -- but make sure to put a choke on the input or you'll have switching noise all over your system.
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Old 7th October 2010, 01:24 PM   #10
peskywinnets is offline peskywinnets  United Kingdom
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While I'm here...with LDO (pwm type) regulators...in a 1/2 rail virtual earth arrangement they seem a little noisy - are there any tips here to tame their noise a little?

Also, you say to put a choke on the input to the regulator? (I would have expected output). What size choke are we talking (value wise) for a low current draw setup.
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