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.

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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