Darlington pair

[Tan9890]

Hi.. I'm basically trying to drive a simple motor using a transistor.. bc547..
The problem i'm facing is, output current is too low.. i need atleast 1 ampere.. can any1 suggest any ideas?
I know about the darlington pair, n how to increase the current gain.. It seems i'm making a mistake while building the circuit in multisim.. PLz give any suggesions that might help..

Also.. keep note that i exclusively want to use bc547 coz its cheap..
thanks in advance

 

[ccurtis]

Although a Darlington pair will increase current gain it is not going to reduce the collector current requirements on the transistor. The bc547 is rated for 100mA max continuous collector current.

 

[Torben]

I think you could parallel 10 (preferably more) BC547s to get the 1A current, as long as the current is equally divided between them. Of course then you're spending over $3 for the BC547s (plus a bit for the extra base resistors), when you could do the job with a single TIP31 for $0.66. (Just using today's prices on Digikey.ca for the example).


Torben

 

[ccurtis]

Yes, agreed. Several can be paralleled but with current sharing concerns and/or complexity issues. See https://accelconf.web.cern.ch/AccelConf/p83/PDF/PAC1983_2935.PDF for a good overview.

 

[Tan9890]

thnx guys.. i'l give i a try tomorrow..
But even with the base resistors delay will b present.. n also the circuit will become huge n complicated to solder, considering 10 bjts..
So jus one more question..

Can i use another transistor? I need both npn and pnp.. Plz suggest some names.. n relatively cheap ones.. This is just a homemede project i'm trying so cant spend much..
Thanks again..

 

[mneary]

You not only can use a different transistor, you should. A TIP31 was suggested, which is an excellent idea. It's available everywhere in the USA for US$0.55 or so. European equivalent is probably BD241 and elsewhere 2SD880.

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