How to get -5V for operational amplifier

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#1
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Hi !

 

I need -5V for 6 OPA to measure 6 analog channels.

 

Till now I was getting -5V form DC/DC converter ISA0505.

It's space consuming and expensive solution.

 

Now I'm trying to use TPS62160 but I have some issues with it and I'm waiting for response form TI.

 

 

So, what can you suggest me to achieve -5V ?

 

 

Thank you ! 

 

Regards !

 

 

 

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What current do you require?
You have two main choices - charge pump or inverting boost converter.

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Or a Max232

 

Ross McKenzie ValuSoft Melbourne Australia

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Another charge pump ic is the NCP1729 Switched Capacitor Voltage Inverter.

 

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Thank you for suggestions !

 

I suppose I need currents up to few teens of mA.

 

OP-a don't require many mA or do they?

 

I've found TPS6400 and it looks simple

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Do you need -5V?

 

Perhaps make 2.5 as 0 for the opamp, so 0=-2.5 and 5V =2.5

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valusoft wrote:
Or a Max232

;)  That was my old-school idea as well.  Back when I was OP's age, many/most micro apps had an RS232 link and a modest supply of -10V came "for free".  Not nearly as common nowadays.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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It'll be pretty noisy, though ?

 

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awneil wrote:
It'll be pretty noisy, though ?

???  The -10V?  Dunno. We've used it in past apps for getting op amps down to the low rail.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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theusch wrote:
That was my old-school idea as well. Back when I was OP's age,

 

Another way we would get a V- rail would be to create an oscillator with an NE555 or even an op-amp and feed a rectifier circuit.

 

 

As Sparrow mentions you could bias the opamp at half the Vs.  Make sure you use Rail to Rail opamps for best accuracy

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Surely you can use a purpose made chip if you really need tens of mA.
I suspect you only need a few mA. In which case you can use an AVR Timer for a charge-pump. You save an i.c. but still have external capacitors and diodes
.
David.

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david.prentice wrote:
I suspect you only need a few mA. In which case you can use an AVR Timer for a charge-pump.

Brilliant!

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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In which case you can use an AVR Timer for a charge-pump.

I've done the same to achieve the +12V needed for an HVSP programmer.  At first I fiddled with software regulation via the ADC, then via the AC.  In the end I decided to regulate with a 78L12.

 

You'll likely need fairly 'clean' power for the opamp, so a 79L05 or similar is probably the best bet.  Might make due with a zener.  However chances are something like the NCP1729 will end up having a smaller footprint and a lower BOM anyway.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Op, what is the *actual* signal range your opamp needs to accomodate? If you are only driving the avr adc, you may only need a small amount of v-, or perhaps none at all.

Tom Pappano
Tulsa, Oklahoma