# Equivalent for 2SB857,2SB858 PNP

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#### mw7198

##### New Member
Hello,

I was hoping someone here knows of an equivalent to the Hitachi 2SB857,2SB858 PNP transistor used in a MW7198 NiCad/NiMH battery charger. I have a datasheet for the Hitachi product( http://nitro.tzo.com:7704/cam/2sb857-2sb858pnp.pdf ).... but I cant get hold of one in Australia, ... does anybody know a common equivalent(possible available from somewhere like http://www.jaycar.com.au/ )

Any and all help appreciated.

Kind Regards

Justin
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#### Sebi

##### Active Member
Use BD650 from this collection.

#### mw7198

##### New Member
Thanks Sebi, Ill pick one of those up and give it a try.

Thank you very much for your help

Justin

#### mw7198

##### New Member
Hello

I have installed the new components and the charger is working well, I have tested the current output and voltage and all is how it should be.... however my only concern is that while charging a 4.8v 1500Mha NiMh pack @ 1 amp the transistor gets up to about 80-90 degrees C ! is that too hot ? Looking at the data sheet it states the "junction temp" can be 150 degrees C....does this mean it can get up to 150 safely ?

Cheers

Justin

#### mozikluv

##### New Member
heatsinking

hello mw7198,

to put your mind at ease, put the pow. trans. on a bigger heatsink, bigger than the one you are using now. :wink:

#### mw7198

##### New Member
Thanks for the reply, The tran. in question is unfortunately not heatsinked !...and the case of the charger leaves very very little room to get one in !, I would really like to use a heatsink(I have quiet a few to choose from lying around) but the only way I can see using one is if I hang the tran.(and extend wires from the board to outside the case) outside the case and attatch a heatsink....which would look a little ugly... but I may have to do it !

Is 90 degrees C too hot for that type of device ?

Cheers

Justin

#### Sebi

##### Active Member
Cloned post deleted.

#### Sebi

##### Active Member
If the transistor work now without without heatsink, and only 90 degrees hot, for proper cooling quite enough about 15...20 quadratcentimeter aluminium plate. The totally closed case avoided.(drill a few 4mm holes both (opposite) sides)
On the 90deg running transistor can work, but this method use only the chinese manufacturer(Hi). In homebrew experience i never enable over 50...60deg. (i designed the devices for 99 years work...)

#### mozikluv

##### New Member
heatsinking

:lol: :lol: :lol: :lol: :lol: hello sebi,

thats the kind of work that i reeally luv, the kind that outlive the person who made it. :lol: :lol: :lol:

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