DC/DC converter advice

Projects General Guidance
1

I'm new to amateur electronics, but getting there slowly...

I have a requirement for a decent -5v rail. Specifically this is to trip a 4052 mux/demux into analogue mode.
I've since tried a simple 555 based inverter and only scraped -3.6v from the 5v arduino power pin thanks to a pretty inefficient circuit.

I then stumbled across these guys:
http://www.rapidonline.com/Electrical-Power/Power-Supplies/DC-DC-Converter-ICs/1W-Dual-output-DC-to-DC-converters-RVFM/72607
The only one that rapidonline stock is a 24 vin -> 12vout ... Rather annoyingly the picture boasts a G01-04D (5Vin -> ±5Vout) which is exactly what I need. But they don't stock them. Nor can I find anywhere that does!

My question is, is there a cheap alternative, or is anyone aware of a UK-based reseller that sell individual units??

PS, I know about the MAX764s, and at £4 a pop, it's not too friendly.

2

It sounds like you only need a small current. A cheaper charge pump inverter would be the Microchip TCM829 (<$1) if you're OK with surface-mount devices, or the Microchip TC7660 if not (still <$1). It's part number 9762680 at Farnell and only £0.55!

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The Aussie Shield: breakout all 28 pins to quick-connect terminals

3

It certainly looks like what I need! :slight_smile:
Until this moment, I'd never even heard of a charge pump.

I'll be ordering a couple of those next week then. Thanks for the help!

4

I know this is starting to now get into the realms of not for this forum, but last question(s), honest! :smiley:

Obviously I need -5V from the +5V, but I know you don't get anything for free!

  1. Will the nearly -5V that I will get from the charge pump IC be good enough for VEE on the HC4052? (Datasheet: http://www.datasheetcatalog.org/datasheets/320/446419_DS.pdf)
  2. I recognise that I'm only going to get close to -5V if the ESR is low on the flying and output caps. I found some 0.06ohm 10uF 25V on farnell that I wonder would do the job?

Thanks for the help this far guys!

5

Should be fine on both counts.

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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

6

I'm switching unamplified audio signals.
In fact, I'm still very much learning, so it's entirely possible I've got this completely wrong and the HC4052 VEE need only be a small negative voltage. I'm honestly not sure.

The datasheet states that VEE is the negative supply. And that VCC - VEE can be 2V - 12V which seems to suggest that my -3.6V will do the trick. I'm not seeing the significance of applying a negative voltage other than to trigger the analogue behaviour. Does the switched signal need to sit in the range VCC to VEE??

7

If you have a source to scrounge old computer motherboards, many of them had -5V DC-DC converters on them. Look for a large black epoxy box with 4 leads. I have a couple of those in my parts bin.