i m using LM317 regulator, may i know that what kind of method i can use in order to get voltage <1, since for the data sheet write that the minimum voltage range will be 1.25V..

thanks...

 

Using that part there is no method that I know of. You might have more luck with an adjustable LDO regulator from Micrel, National, TI, or Maxim.

 

You simply require a negative supply as well, so the bottom of the regulator is below zero volts. You're basically moving the zero reference point - it's a technique used for PSU's that vary right down to zero volts.

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You can use a DC/DC converter with a voltage reference. It's a trick someone showed me on here about a week ago. Look for a post by me about DC/DC converters and it will have the link. We used it at work to get down to 0.2V regulated output at 50% efficiency from 3V in IIRC.

 

just put Two diodes in series with the output. You will lose a little bit of stability, But the voltage drop across these diodes will allow you to get Close to Zero volts out.

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This is how I'd do it anyway.
http://www.electro-tech-online.com/a...-15v-lm317.pdf

You do need a negitive supply but this is noramally easy as you're probably running it from the mains or a PC power supply; if not then you can build a negitive supply from a 555 timer.

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Is this a <1V signal? Or <1V power?

 

That's true, if you want a signal then use an LM7805 and a potential divider followed by a non-inverting buffer.

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i need <1V for power supply and also signal...

how can i get negative power supply?if i use 9V battery, then the voltage will become 0-9V...how to change it become negative voltage?

 

How much current do you need? If it's less than about 200 mA, I would use the obsolete and extremely cheap LM324 (or TL072) driving a 2N2222 in emitter follower configuration.

 

The output of an old LM324 quad opamp or an old LM358 dual opamp goes to ground if it has a single supply voltage.

The output of a TL07x does not go to ground, it goes to about 1V above ground if it has a single supply voltage. So adding an emitter-follower will not produce an output down to ground.

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Although the TL07x won't sink useful current closer than 1V from ground, it stops sourcing as well. This meets the 1V output requirement. It might need a pull-down resistor, though.

 

An op-amp that can swing to 0V won't be any help in the circuit I posted as the ADJ pin needs to be held at -0.25V for an output of 1V so a negitive supply is unavoidable.

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try to use a single cell for -ve refby connrcting its +ve to ground and the lm317 can now be referred to -1.5V -- thus minimum can to to zero-- a possible method for explanation only is attached here - this is with courtesy of National semi datasheet info--


Sarma

 

I can see you do not have a negative voltage so: see attached file.

You must choose the correct op-amp. Most op-amps will not work with their inputs near the same voltage as the supply pins. ( If the power supply is 0 to 12 volts then many will not work if either input is less then 2 volts or more than 10 volts.) You need to look for an op-amp that has a “common mode input voltage” that includes the negative supply. There are some amps like that, you might start out looking at MicroChip for low voltage op-amps.

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