[thegopher]

Anybody got any ideas to tweak 3 pin regulators to the max, other than those covered by data sheets?

 

[Dreamslacker]

1) polish the back
2) clean with alcohol
3) apply Artic Silver 3 thermal compound
4) mount a big heatsink
5) screw real tight to ensure maximal metal to metal contact area and squeezing out of excess compound
6) clean off excess compound

That should improve operating temperatures, leading to higher output current/ voltage (since temperatures are lower). Really overkill though. Especially the compound part.

 

[ppl]

put small 1-2 ohm resistors in series with the output and within the Feedback loop to improve stability. i have posted about this befor but can't remember where

 

[thegopher]

ppl-

Are there any limits on input and output capacitance for stability with this method and are LDO regs like the LT1085/1033 more susceptible to stability problems with high values of output C than the LM317/337 types?

 

[ppl]

The LT-1085 & LT-1033 are just an improved version of the LM series most all operating concerns are similar for Both. The LT reg's do offer slight improvements over the LM types However for most applications thay can be considered improved Replacements for the LM series. Also look at the Schematics on the data sheets and see the topology is also similar in fact about the same.

The reason for the resistor on the output is to allow the use of low ESR electrolytics and Film capacitors on the output. Input considerations remain the same

 

[eric343]

Also, don't mount it using the hole! I've seen a bunch of people mount TO-220s like this (including Mr. Gilmore! [though his method largely eliminates the issues encountered]). It places pressure in the wrong place; the chip is in the plastic! Use a piece of aluminum stock or u-channel to press the /whole/ transistor against the heatsink.

When you use a screw through the hole, what happens is that the transistor can get slightly tilted towards the heatsink, "lifting" up the part of the tab where the chip is away from the heatsink, and reducing thermal efficiency.

http://sound.westhost.com/heatsinks.htm#flat%20packs

Oh, and paint that shiny anodized aluminum black using oil paint.

 

[thegopher]

I've seen the two resistors which set the output voltage on adjustable regs replaced by a diode and current source. What's the skinny on that?

Can anyone post a schematic and/or suggest part numbers?

 

[ppl]

See the att. The Zener is whatever output voltage you need plus 1.2 Volts. select the Jfets for an Current of about 10 Ma. MPF-103 I think is in that range. add a 1-2 ohm or less resistor between U1 out and Q1/C1 do the same for U2's out and Q2/C2. make sure the regulators inputs are bypassed as recomended in Data sheet or located real close the the Filtor caps.

 

[puppyslugg]

For those having trouble locating the MPF-103 fet, try 2N5457. Mouser has the 2N5457's in stock.


CORRECTION:

It appears the cross referenced 2N5457 will not provide 10ma of sourcing. An option would be to use selected 2N5486's.

 

[thegopher]

ppl- is there any advantage in cascoding the current Source FET like you advocate for biasing opamps into class A?

If so, could you possibly post a schematic.

Many thanks

Gopher