Boat autopilot remote (question about transister choice)

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Discussion Overview

The discussion revolves around the choice of transistors for building an autopilot remote for a boat. Participants explore the specifications and interchangeability of different transistor models, specifically comparing the 2N4402 and 2N4400 with the BC337 and BC327. The focus includes technical specifications, such as Continuous Collector Current, and the implications of using different types of transistors (NPN vs PNP).

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • Peter inquires about the suitability of using BC337 and BC327 transistors instead of the specified 2N4402 and 2N4400, questioning the importance of their specifications.
  • Some participants clarify that the BC327 is a PNP transistor while the BC337 is an NPN transistor, correcting initial confusion.
  • Peter expresses that having a higher Continuous Collector Current rating may be beneficial, suggesting it allows for handling more current.
  • Another participant notes that as long as the transistor meets basic requirements, the specific choice may not significantly impact the circuit's function.
  • Concerns are raised about checking the frequency response of the replacement transistors if high frequency signals are involved.
  • There is a reminder to verify the pinouts of the transistors, as one may not follow the standard EBC configuration.

Areas of Agreement / Disagreement

Participants generally agree that the type of transistor (NPN vs PNP) is crucial, but there is no consensus on the overall interchangeability of the transistors or the implications of their specifications. Some participants believe that higher ratings are advantageous, while others emphasize the importance of specific characteristics.

Contextual Notes

Limitations include potential misunderstandings about transistor types and specifications, as well as the need for careful consideration of circuit requirements and configurations.

pslarsen
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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
 
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Aren't the BC327 and BC337 both NPN transistors?
 
hutchphd said:
Aren't the BC327 and BC337 both NPN transistors?

No, the BC327 is a PNP and the other a NPN
 
I remember myself asking very similar question and then reading this: https://www.edn.com/design/analog/4429969/Choosing-Transistors
 
Borek said:
I remember myself asking very similar question and then reading this: https://www.edn.com/design/analog/4429969/Choosing-Transistors

Hi Borek

Thanks for the reference, but I don't feel that it answers my question specific to the circuit that I'm looking at.

Br, Peter
 
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
 
pslarsen said:
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.
 
Borek said:
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
 
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
 
  • #10
Many thanks
 
  • #11
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.
 
  • #12
Ok I will