Author Topic: Limiting a LDO (Read 11530 times)

warlordxxx · « **on:** April 11, 2012, 07:22:56 PM »

Hi me again with yet another question

- Can a 5v regulator such as the ucc283 be limited to 4.2v output with a resistor (or diode) and what value resistor would be needed please and thank you

Breaktru · « **Reply #1 on:** April 11, 2012, 08:01:56 PM »

Quote from: warlordxxx on April 11, 2012, 07:22:56 PM

Hi me again with yet another question - Can a 5v regulator such as the ucc283 be limited to 4.2v output with a resistor (or diode) and what value resistor would be needed please and thank you

The UCC283TD-3 and UCC283TD-5 are fixed at 3.3v and 5v.
The UCC283TD-ADJ regulates the output voltage programmed by an external resistor ratio. Output voltage range is: ?0.3 V to 9 V

Calculating resistors:
(R1+R2)
VOUT = 1.25 V x ______
R1
See datasheet: http://www.ti.com/lit/gpn/ucc283-adj

warlordxxx · « **Reply #2 on:** April 11, 2012, 08:15:38 PM »

Quote from: Breaktru Admin on April 11, 2012, 08:01:56 PM

The UCC283TD-3 and UCC283TD-5 are fixed at 3.3v and 5v.
The UCC283TD-ADJ regulates the output voltage programmed by an external resistor ratio. Output voltage range is: ?0.3 V to 9 V

Calculating resistors:
(R1+R2)
VOUT = 1.25 V x ______
R1
See datasheet: http://www.ti.com/lit/gpn/ucc283-adj

Thanks Breaktru it's of the fixed voltage variety (TD-5) that'll teach me for not putting up the whole part number

any ideas on a good adjustable regulator not that i don't like the TI stuff it's just that i don't want to just order a single all the way from the states ?

Breaktru · « **Reply #3 on:** April 11, 2012, 08:24:38 PM »

Personally I wouldn't use an LDO regulator for a mod. They are not very efficient. It is possible to get the 5v down to 4.2v with a resistor but it would mean even less efficiency. More heat more battery loss.

warlordxxx · « **Reply #4 on:** April 11, 2012, 08:26:26 PM »

ok so what would be the best ie most efficient way to get from 2 battery input to regulated 4.2v output please

Edit: considering i'm using 2x14500's in a 3xaa box

Breaktru · « **Reply #5 on:** April 11, 2012, 08:38:21 PM »

PTR08100w, PTR08060w or the OKR-T/6, T/10, T/3

warlordxxx · « **Reply #6 on:** April 11, 2012, 09:13:34 PM »

Quote from: Breaktru Admin on April 11, 2012, 08:38:21 PM

PTR08100w, PTR08060w or the OKR-T/6, T/10, T/3

Many thanks again breaktru for all the help - ordered a T/6 now just need to figure out how to wire the sucker when it gets here lol

Breaktru · « **Reply #7 on:** April 11, 2012, 09:32:53 PM »

Quote from: warlordxxx on April 11, 2012, 09:13:34 PM

Many thanks again breaktru for all the help - ordered a T/6 now just need to figure out how to wire the sucker when it gets here lol

It's easy. Just need a 200 ohm trimmer and a 220 ohm resistor. No caps needed. And of course the usual P.B., batt conn, etc...
We are here to help. Several members here have experience making mods with it also...

warlordxxx · « **Reply #8 on:** April 12, 2012, 05:22:54 AM »

Quote from: Breaktru Admin on April 11, 2012, 09:32:53 PM

It's easy. Just need a 200 ohm trimmer and a 220 ohm resistor. No caps needed. And of course the usual P.B., batt conn, etc...
We are here to help. Several members here have experience making mods with it also...

But surely the trimmer would vary the voltage i'm after 4.2 only lol