-5 V power supply for OPA

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#1
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Hi guys !

 

How to realize -5 V supply for OPA237 or any other ?

 

 

I've achieved this with 

 

http://uk.farnell.com/tracopower/tes-1-0521/dc-dc-5v-5v-1w-smd/dp/1635251

 

 

and it works.

 

 

I'm wondering if there is better and cheaper way to do this?

 

 

Sorry for awkward question, I don't have any experience with this.

 

 

Thank you !

 

 

 

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If you don't need much current, and you don't need the full -5v, you can make a voltage inverter using a couple of diodes and a couple of capacitors driven by a square wave from a spare MPU pin.

 

Or, in the last few weeks I had notification of a new op-amp designed with it's own on-board -ve rail generator designed for easy use with MPUs. Trouble is, I can't find the email!

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Ah, found it...

 

http://www.maximintegrated.com/e...

 

 

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Are you starting out a new design, or just adding this to an old one?

 

What else is available in the rest of the system?

 

Mains or battery powered?

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You could also consider the MAX232 chip(s).

 

Ross McKenzie ValuSoft Melbourne Australia

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valusoft wrote:
You could also consider the MAX232 chip(s).

If the noise is OK

Top Tips:

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Probably no worse than the couple of diodes, cap and MCU drive...

 

Ross McKenzie ValuSoft Melbourne Australia

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Thank you for replays !

 

It's new design.

 

I'd like to measure grid voltage 230 V AC.

 

I have +5V, +3,3v and +3V and board is mains powered.

 

 

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For a new, mains-powered design, use a centre-tapped transformer to give you a proper bipolar supply

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+100

Ross McKenzie ValuSoft Melbourne Australia

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I can see why you would need an isolated input, but not a bipolar supply. You just need 5V from a wall wart to run the microprocessor. You need a voltage divider on the secondary of the transformer from the mains to sniff the voltage. I'd just forget about the negative part. Put a reversed biased diode on the input. Read the peak voltage. Double it. Thats what youd see with a bipolar front end.

 

 

Imagecraft compiler user

Last Edited: Fri. May 8, 2015 - 05:00 PM
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Agreed.

 

If the circuit is NOT isolated, i.e. it is live attached to the Mains, then put a series diode on the 230 V AC signal, which then feeds the resistor divider.

Don't put the diode after the resistor divider.

This way the voltage drop from the diode is negligible.

 

That said, feeding the Mains into your PCB can be very dangerous.

There are many previous Threads which discuss the risks.

 

Using a small transformer to isolate the voltage to the uC from the Mains would be a VERY GOOD idea.

Use a Mains to 12 or 24 V transformer, for example.

Again, feed it through a diode, and a resistor divider to then feed the ADC input.

You will likely want a small load on the transformer.

 

 

JC