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BC457 instead of TIP31? Answered

for the circuit in the pic can I use BC547 instead of TIP31

6 Replies

icengBest Answer (author)2013-08-31
  • BC547 - PEAK ( 45V & 100ma ), Min_GAIN =110
  • TIP 31 -- PEAK(40V &  3000ma),  Min_GAIN =25

The Tip 31 poor gain leads one to try using the BC547 although there are
Far Better transistors to use in this app.


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iceng (author)adarshnarsaria2013-09-01
  • NPN - ZTX450 - PEAK (45V & 1000ma) - Min_GAIN = 300 - Super_Low_FWDrop=o.25V
  • NFET - 2N7000 - PEAK(60V & 200ma) - Gain _4VoltGS_Saturates=300ma

I have included PDFs of both TO-92 transistors
They are available at Mouser and DigiKey .
A low forward voltage in a transistor is desirable and means less power dissipated, 
runs cooler and can handle more LEDs in certain low DC voltage battery situations.
And you want to have about 100 ohm in series with your LEDs !


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Josehf Murchison (author)2013-08-28

First of all I hope you mean BC547 and not BC457 because a BC457 is a crystal oscillator.

Then again TIP31 is a 3 amp and BC547 is a 100 mill amp which should handle the 20 to 30 mill amp of the LEDs however at best the speaker will only work as a buzzer.

You can find the datasheets at these two sights.



I find this sight great for parts, free datasheets, and hard to beat prices.



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steveastrouk (author)2013-08-28

Not unless you put two into a Darlington connection.

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