how to get <1V by using regulator

[meera83]

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...

 

[Papabravo]

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.

 

[Nigel Goodwin]

Using that part there is no method that I know of.

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.

 

[Speakerguy]

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.

 

[chemelec]

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...

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.

 

[Hero999]

This is how I'd do it anyway.
https://www.electro-tech-online.com/attachments/0v-to-15v-lm317-pdf.9790/

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.

 

[dknguyen]

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

 

[Hero999]

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

 

[meera83]

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?

 

[mneary]

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.

 

[audioguru]

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.

 

[mneary]

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.

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.

 

[Hero999]

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.

 

[mvs sarma]

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...

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

 

[ronsimpson]

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.

 

[mneary]

That's the circuit I would use an LM324 in. Sorry I didn't provide more detail...

Apparently my previous post was interpreted as suggesting that an op amp with 0V negative supply would somehow provide a -ve output.

 

[Hero999]

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.

There are two problems with that circuit.

One, you need a 0.25V reference to give you the 0.25V output.

Secondly, the ADJ pin needs -0.25V to give 1V, your circuit gives +0.25V which would give an output 1.5V.

Like I said before, you need a negitive supply which can be made form a 555 and a couple of diodes and capacitors.

 

[mneary]

If you take ronsimpson's circuit and set the reference to 1 volt, you have a 1 volt supply. No LM317. You do need to supply the R1/R2 divider with something stable enough for the output that you want.

 

[FRIED]

Use an LM10
**broken link removed**

 

[Hero999]

Which is fine to use without a booster if you only need 20mA.