3 replies to this topic

[rmjlmartin]

I have a question that I'm hoping someone might know the answer to.

 

I've been learning about controllers over the last several years, researching, learning how they work, tinkering, and even built several. (I'm certainly not an expert, but that process inspired the question.)

 

In my research, I've noticed that, while most controllers built here in the US that use BJT transistors seem to use NPN single transistors (or a parallel pair, still functioning as a single transistor, vs a Darlington pair), our fellow racers across the pond seem to prefer a PNP Darlington. Does anyone know why that is? No one I've asked so far knows. A friend and I have speculated that maybe there's some characteristic of a PNP circuit that makes it preferable for flat track racing, which seems to be more prominent over there. Or maybe it's just as simple as the first good electronic controller in the UK was built with a PNP transistor, everyone else copied them, and that's what everyone has used since, and the same thing over here, except with an NPN transistor?

 

A fair amount of my information has come from this site- https://www.slotcarr...ntrol/index.htm It's dated 2009, with minor updates in 2025, so it's obviously mostly a few years old, and may not be completely up to date, so maybe the trends have changed since some of it was written? I know there are pros and cons to NPN and PNP circuits, as well as a single transistor vs a Darlington, but does anyone know why different circuits seem to be preferred here in the US and over in the UK?

[Jim Difalco]

Jason, google "advantages of NPN transistors over PNP transistors" and you will get a long list of differences. Do the differences mean anything? Nope.

 

It is probably more likely that a UK builder picked a PNP, it was successful so it was copied. NPN transistors are more plentiful in types and less expensive.

 

I know when I started building controllers I had many racers wanting to know if my controllers used a Darlington transistor. They just got it into their head that this was some sort of important advantage for some reason.

[rmjlmartin]

Thanks Jim, I was hoping that you might reply, since I know you've been building electronic controllers for a long time. Were you one of the first?

 

So for you, choosing NPN over PNP was simply economics? From my own experience, I'm sure you're right that the differences have minimal effect on actual real-world performance. There are a whole lot of things, like transistor types, that people make a lot of claims about their preference being infinitely superior, that I think really don't make much, if any difference when it comes down to it. They may "feel" a bit different, and some people are more comfortable with one thing or another, but a lot of it comes down to preference, as long as the controller is capable of handling the cars you want to run.

[Jim Difalco]

The single 2N5302 transistor with the silver metal case I used on my Genesis 1 controllers was picked because it had the highest amperage, 30, and heat dissipation before you got to the super expensive 50 amp transistors in the TO-3 case. The TO-3 case has been generally phased out of production over the last 5 years in favor of the type case that is on the TIP35C transistor I use now. It has a lower amperage of 25 but a good heat dissipation. Using two transistors has increased the amperage and heat handling of my controllers as well as the reliability of the transistors many times over.

 

One caution to racers is if you replace your want to replace one of my transistors with one from a local electronics store you are taking a chance on getting a different sensitivity range or poor reliability. I only use ON Semiconductor brand as it has proven to be very reliable and consistent. For one small batch I purchased the STI brand, which is well known, and the transistor output was very low compared to the ON Semi resulting in a much lower sensitivity range. It made the controllers feel very sluggish. I have also seen 15 amp transistors substituted for my silver case transistors that would of course reduce the controllers reliability. So beware if you want to do your own repairs with non standard parts.