psu pass transistor emitter resistors

[p.larner]

On some i see 0.1 ohm used others use 0.22 ohm,why the difference even tho the same pass transistors are used?.

[Xena E]

On some i see 0.1 ohm used others use 0.22 ohm,why the difference even tho the same pass transistors are used?.

Specific examples? Schematics?

Current sampling? or emitter degradation for balancing?

First instance: value depends on direct sampling level required.

Second instance: design choice based on pass device specifications, covering expected spread between parralel devices, and how many there are.

Regards,
X.

[Kleinstein]

The required size of the emitter resistors to improve current sharing depends on the heat sink (thermal coupling) and spread or parts, but also the voltage (higher voltage needs higher resistors). The choice is often more like a rought estimate and some prefer smaller values as this can use lower power parts in the hope to have matched transistors, while other play it safe and use larger resistors.
Even with a perfect match to start with on still needs the resistor as the system can become unstable (positive feedback with too much gain) and run away with too little resistance.

[Zero999]

I bet this is about the 723 again isn't it? I repeat. You'll get better responses by keeping it all to one thread!

In many circuits, the emitter resistors also double as current sense resistors. This is common in linear regulators, as well as amplifiers which have over-current protection. In some cases, the current limit circuit is only connected to one of the resistors, but it's often better to connect it to all of them, each via another resistor, to get the average of all of the currents.

[iMo]

I bet this is about the 723 again isn't it? I repeat. You'll get better responses by keeping it all to one thread!

The OP has got this message several times already, afaik, still polluting the forum with new threads..

[Xena E]

I bet this is about the 723 again isn't it? I repeat. You'll get better responses by keeping it all to one thread!

The OP has got this message several times already, afaik, still polluting the forum with new threads..

Just realised, seen them in Beginners, Projects, and Repairs, mostly post and run. Perhaps the OP is a blanket bomber: posts the same Qu's across several sites and forums then forgets

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