Low Drop Off voltage regulators - Electronic Circuits Projects Diagrams Free

walshlg · 25th April 2008, 05:35 PM

How do these things work? From what I'm reading it appears tha you can get say 11.7V output from a 12V source at 1A -> is this correct? How does it work if you need 1.7V across the transistor minimum? I'm considering using this as a voltage follower in place of a power transistor as I could get a higher output voltage.

[I'm trying to make a fan speed controller buffer to handle multiple fans on a single controller line (eg there are 3 fans on my PC watercooling radiator) but I want to be able to get as close to 12V as possible for max speed when things get hot. Pulse width modulation (with 3 lead fans) makes the tach signal worthless so can't go that way btw]

speakerguy79 · 25th April 2008, 05:45 PM

They use a different topology than the standard NPN pass transistor regulators (like LM317s and 7805s). It probably uses a single P type FET as the pass transistor.

**Nigel Goodwin** · 25th April 2008, 08:50 PM

Quote:

Originally Posted by speakerguy79

They use a different topology than the standard NPN pass transistor regulators (like LM317s and 7805s). It probably uses a single P type FET as the pass transistor.

Or (more likely) a PNP transistor, as used in 12V portable TV's for decades.

ericgibbs · 26th April 2008, 07:49 AM

hi,
This was recently posted by a member. 'thespeakerguy'

Explains standard Vregs and LDO.

speakerguy79 · 26th April 2008, 06:54 PM

actually that was me

ericgibbs · 27th April 2008, 07:32 AM

Quote:

Originally Posted by speakerguy79

actually that was me

Quote:

This was recently posted by a member. 'the speakerguy'

hi,
I did post the credits naming you..

Useful pdf.

walshlg · 29th April 2008, 04:54 PM

Thanks! I really liked that tutorial. I was just wondering about the physics of the gating etc as to how the PNP can turn on with such a small voltage drop. Sometimes I can understand such explanations like the basics of how transistors work, so I was just wondering what is different about this configuration. Just curious.

Hero999 · 3rd May 2008, 07:04 PM

If you use an n-channel MOSFET and a small boost converter so you can drive the gate at a higher voltage than the supply, you can get a very low drop out voltage.

It's a wonder that some ICs don't use this technique. There could be an on-chip voltage doubler so all you need to do is add a couple of ceramic capacitors to give an ultra low dropout regulator.

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25th April 2008, 05:35 PM	(permalink)
walshlg	Low Drop Off voltage regulators How do these things work? From what I'm reading it appears tha you can get say 11.7V output from a 12V source at 1A -> is this correct? How does it work if you need 1.7V across the transistor minimum? I'm considering using this as a voltage follower in place of a power transistor as I could get a higher output voltage. [I'm trying to make a fan speed controller buffer to handle multiple fans on a single controller line (eg there are 3 fans on my PC watercooling radiator) but I want to be able to get as close to 12V as possible for max speed when things get hot. Pulse width modulation (with 3 lead fans) makes the tach signal worthless so can't go that way btw]

25th April 2008, 05:45 PM	(permalink)
speakerguy79	They use a different topology than the standard NPN pass transistor regulators (like LM317s and 7805s). It probably uses a single P type FET as the pass transistor.

26th April 2008, 07:49 AM	(permalink)
ericgibbs	hi, This was recently posted by a member. 'thespeakerguy' Explains standard Vregs and LDO. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 12:24 PM.

26th April 2008, 06:54 PM	(permalink)
speakerguy79	actually that was me

29th April 2008, 04:54 PM	(permalink)
walshlg	Thanks! I really liked that tutorial. I was just wondering about the physics of the gating etc as to how the PNP can turn on with such a small voltage drop. Sometimes I can understand such explanations like the basics of how transistors work, so I was just wondering what is different about this configuration. Just curious.

3rd May 2008, 07:04 PM	(permalink)
Hero999	If you use an n-channel MOSFET and a small boost converter so you can drive the gate at a higher voltage than the supply, you can get a very low drop out voltage. It's a wonder that some ICs don't use this technique. There could be an on-chip voltage doubler so all you need to do is add a couple of ceramic capacitors to give an ultra low dropout regulator. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez