LM317 question low voltage range input

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jabberwocky_one

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Hi I would like to know if the lm317 works from 4.2V-3.3V regulated down down to 3.0V. Multisim is unable to simulate 4.2V->3.0V with LM317H, so I was wondering if the hardware actually works.

It outputs a shape like so:
**broken link removed**

Lowest woltage was 1.99V.
Does the real world equivalent behave so?

Thanks in advance.
 

The dropout voltage depends on the load. At 1A it is typically around 2V meaning you need at least 5V in to get 3V out. Even at 20mA the dropout is 1.5V. You need a low dropout regulator (LDO).

Keith.
 

You need a low dropout regulator (LDO).
Click to expand...
Yes. Unfortunately, the term isn't very specific. You can find so-called LDOs, that have drop-out voltages above 1 V. So you may
want to read the datasheets yourself and find a part with a suitable specification. Manufacturer's search engines can help you to find it.
 


Very true. I was given the specification of the LT1083 the other day which is called a low dropout regulator. I couldn't believe it when I saw the dropout was 1.5V!

Keith.
 

What are the usual dropout values may I ask?
If it's 1V then... oh gosh does that mean I am gonna power my PIC with 3.3V-1V= <2.3V?
 

With a low dropout one you should be able to get less than 0.1V dropout.

Keith

Added after 12 minutes:

If you look here, there are some well below 100mV:

**broken link removed**

Keith.
 

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