simple negative rail gen.

Jan 21, 2005 3 Replies
J

Switched capacitor (charge pump) supplies are never very efficient, just very simple. I think you should look at an inverting supply based on a flyback inductor and something like the LM2594.

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It can supply up to 200 mA of -5 volt with a 5 volt input. See figure 25. You may need a second stage of LC filter to get the ripple down to 10 mV.

John Popelish
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T

-- or just use an LC (or ever RC) filter following a switched cap filter.

Tim Wescott Wescott Design Services http://www.wescottdesign.com
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A

I'm looking for a cheap simple method to get unregulated -5V 30mA from



+5V supply, but output ripple must be < 10mV. I've read about a using a standard inductor based DC/DC stepdown and connecting the supply ground to the regulator's output. There devices like the LM2664 charge-pump voltage inverter, but switched capacitors are noisy (large ripple current in output capacitor). Is it possible to replace the capacitor with an inductor in one of these switched capacitor converters ?

Adam



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A

Thanks, I checked out Fig 25 in the LM2594 sheet. It looks like it'll fit the bill. But then I found the newer LM2734, which is much faster, smaller and doesn't cost any more. It seems manufactures of power supply IC are superseding their previous products at such a rapid rate that it has resulted in a obscene number of devices existing today.

Adam

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