Boat autopilot remote (question about transister choice)

  • Thread starter pslarsen
  • Start date
23
1
Hi,

I'm about to build an autopilot remote for my boat, manual found here:
http://www3.sympatico.ca/ericn/Files/Other/DIY Autohelm ST4000.pdf

In the scheme I need to use two transisters, a 2N4402 (PNP) and a 2N4400 (NPN) as illustrated here:
circuit st4000.PNG


As I don't have these transisters can I use a BC337 and BC327 which is what I have. I guess what I'm asking do the specs of the transister matter? Both have emitter voltage of 5V but mine have a Continuous Collector Current of 600ma rather than 200ma on the sketch above. But in the sketch, aren't they just used to re-direct current in this case really? Does the Continuous Collector Current matter?

Kind Regards,
Peter
 
Last edited:
493
175
Aren't the BC327 and BC337 both NPN transistors?
 
23
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Aren't the BC327 and BC337 both NPN transistors?
No, the BC327 is a PNP and the other a NPN
 
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23
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I personally don't see any reason why they should not be interchangable and I guess its only a plus that my Continuous Collector Currents are rated higher than the ones in the sketch as I suppose it means that they can handle more current without the magic smoke..

Br, Peter
 

Borek

Mentor
28,013
2,518
Thanks for the reference, but I don't feel that it answers my question specific to the circuit that I'm looking at.
Not directly, but it explains how to choose the transistor and why in most cases - as long as you follow some simple rules - choice doesn't matter much.
 
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Not directly, but it explains how to choose the transistor and why in most cases - as long as you follow some simple rules - choice doesn't matter much.
I guess what its sayning that the current out is the sum of current in and since my trasistor choise has nothing to do with the currents flowing into it then the only thing that matters is whether is a NPN or PNP as long as its rated to survive the currents in the system.

Br, Peter
 
493
175
If your replacement capacity is bigger you seldom get in trouble. If there is any high frequency in signal be sure to check freq response of replacement. Good luck
 
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Many thanks
 
493
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Also be careful to check the pinouts on the transistor: I think one of your list is not the "standard" EBC configuration. Be sure to check.
 
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Ok I will
 

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