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Old 16th August 2004, 08:54 PM   #1
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Default Low power supply (+/-15VDC)

Here's a question... I just want a low power supply for signal processing, max of a couple dozen op-amps. Not that much current required, but I do want +/- rails.

+/-15VDC would be ideal, however, I'd put up with +/-12V in a pinch.

Of course a SMPS would be a nice thing, but given my lack of success at finding a transormer core, and the low power actually needed, this may be overkill for the application. (Of course I'd preffer overkill to underkill.)

I've seen schematics around for 555 based inverters, which provide the -12V (Or thereabouts) from +12V. This seems to show some promise as being simple, and suitable.

I'm thinking about taking my front stage off of the passive crossover, and bi-amping it. I'd like to use something like Rod Elliot's Project 09 24dB/octave L-R crossover. Just having experienced how much better the 12dB/Octave passive crossover is than the crummy 6dB/octave ones, I'd expect a nice improvement in sound quality and clarity. The stumbling block is that I need a power supply to do it.

The other project that I'd like to work with is Rod's Project 84 8 band subwoofer EQ.

Any suggestions for a power supply?
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Old 16th August 2004, 09:05 PM   #2
maylar is offline maylar  United States
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Op amps can vary a lot in power supply current. And if you want to drive RCA cables, you should strive for 100 ohm source impedance or better, which relates to power. I only mention these things to make you think about what size power supply you really need.

That said, there are self-contained power supply modules available from a number of electronics suppliers. Small size, +/- 15 from 12V in. Go to www.digikey.com and look under power supplies->dc-dc converters. I remember seeing them reasonably cheap.
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Old 17th August 2004, 08:08 PM   #3
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It looks like you only need a few watts of power. You could try something like this schematic:

[from www.bobblick.com]


Click the image to open in full size.

You can make some changes though.
1. You don't need a high power/specialized core for this supply.
2. You don't need an IRFZ44, you need more like an IRF510
3. Use inexpensive 1 amp schottky or fast recovery diodes [like the 1n4933]
4. If you nix the 5v rail, the feedback to the LM3524 should go through a resistor divider [potentiometer] to your +15v out so that you get 15v out. Regulation is a good thing with opamps...

If you don't want to use this, you could use a switched capacitor charge pump to get the supplies but it wouldn't be much simpler IMO.
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Old 24th August 2004, 04:23 AM   #4
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Oh well. I decided to take an "easy" way out and just got some DC converter ICs from Maxim IC. I ordered two sets which should get me a regulated +/-15V, and +/-12V at about 1.5A

That ought to do it.
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Old 25th August 2004, 03:49 AM   #5
labjr is offline labjr  United States
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If this is for a car and you already have an amp in the car, I'd tap off the power supply in the amp. Just use a couple of regulators for positive and negative supplies.

Or you could use another small amp for the power supply only and build your project in the amp case.
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Old 25th August 2004, 05:11 PM   #6
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I had considered tapping off from the amp power supply, but the amps are in the back, and this project is intended to go in the center console (or glovebox.)

I also considered buying a cheap amplifier and just using its power supply, however, since the power supply is usually built on the same board as the amplifier, separating them to make room for my project becomes problematic.

I ordered the Maxim chips as samples, so they're free. If this works out, and seems viable, then I'll see where that takes me.
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