At 09:55 AM 6/25/2004 +1200, you wrote:
>Without going down the whole reverse engineering, desgn calculation
>path, does someone have a simple, rule of thumb value for emitter
>resistors to promote current sharing in paralleled bipolar transistors ?
>
>Now that I actually need 5A out of my 5A bench supply (Wonix YW-
>APS305 from Dick Smith for those who may also have one), I find that
>they have 2 2N3055's in parallel (all three leads) and invariably, one of
>them cooks and dies. Pity they put thermal sensing on the other one.
>
>My immediate problem has been solved with the lead acid capacitor,
>but it would be nice to eliminate the problem for next time. Any top of
>the head values ?
>
>Thanks,
>
>Steve.

Try about 100mV across each ballast at full current. If that's at 2.5A
each, then about 0.04 ohms  at 1/4W (use 1/2W or better rated, non inductive).

For example, these are about $1.50 each US in one-off:
http://www.ohmite.com/catalog/pdf/10_series.pdf

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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