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find a suitable NPN transistor part number =?

Former Member

HI expert ,

can you propose a suitable NPN transistor part number =?

My circuit diagram is that this NPN collector terminal is connected to +15V DC power ,then this power will drive a resistor and a LED ,then finally reach to NPN,

so can you propose a suitable NPN part number ?

 

thanks

Choo

image

  • 0

    Hello chow wei,

     

    There are at least two serious problems with your circuit,

     

    The NPN transistor at the top left will be destoyed because you are applying 5V between base and emitter, you need  a resistor in series with the base to limit the current, if you are aiming for say, 20mA in the LED then a good base current would be 1mA so the series resistor should be about 4k7.

     

    The NPN transistors in the bottom row will not share drive as you have drawn them, each one needs its own base resistor - once again 4k7 would be a suitable value.

     

    For the transistors pick and NPN part rated at 30V or more, 100mA minimum

     

    The cheapest suitable types from Farnell are: 2N5551, 2N4401,BC337

     

    The BC337-25, (Farnell 1228215) should be easily available.

     

    As an alternative yoiu could use MOSFETS which don't need the base resistors,  2N7000 would do nicely and are cheap.

     

    There may be other issues with your circuit but I can't tell since you don't say what it is meant to do.

     

    MK

  • 0

    It looks like your circuit is lighting many LEDs at once.  If that's the case, since you have +15V available, you might be better off connecting groups of them in series and driving them using current sources.  This will probably give more consistent lighting than a parallel circuit, and you won't waste power dropping approx 12V across resistors.

  • 0 in reply to michaelkellett

    Hi : Michaelkellett

     

     

     

    Base on the below circuit, what type of Part Number  for LED  can be used ?

     

     

     

    Thanks

     

    Chow

  • 0 in reply to michaelkellett

    Hi Michael ,

    Good day to you !

     

    Thank you for your advice on NPN part number.

    I will add a resistor 4k7 ohm series-connected to top left LED's base .

     

     

    Could you suggest LED part number  as shown  Circuit diagram.

    For resistor of Rx/Ry/Rz and Ra /Rb at LCD,,  Rc/Rd at Relay ,,can use how many Ohm ??

     

    thanks!

     

    image

    Thanks

    Chow

  • 0 in reply to Former Member

    You need individual base resistors for all the transistors in the bottom row as well.

     

    I can't suggest an LED type unless you can tell me what your ciruit is trying to do.

     

    If there are no other connections to LEDs which are not shown on your circuit then you can put the LEDs in series as suggested by John and make things a lot simpler.

     

    To find LEDs yourself use the search tools on the Farnell website - if you know the kind of package and colour you want and nothing else matters mauch then the website can sort according to price, start looking at the cheapest ones until you find one that looks OK.

     

    MK