Replacement for BD230 Transistor?

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Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 5:26 pm

This is for a model train set Relco that seems to have died. The BD230 is an NPN power transistor (1.5A 80V) with a datasheet available from Phillips, but doesn't seem to be a Digikey part. Measuring in circuit, I'm seeing a short between base and emitter, so I suspect that is the problem. Appreciate any pointers from hardware designers on a suitable replacement. I've found a place that sells them for TV repair online, but I'm wondering if I can through in something pretty generic and cheap here. I can share the circuit diagram if required.
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Re: Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 5:46 pm

Hard to say for certain without the schematic, but any NPN power transistor with the same physical package dimensions and similar (or higher) current and voltage handling specs would probably work. Pretty much the only other parameter which might get you in trouble is the current gain (commonly referred to as beta) of the transistor -- if the beta of the replacement is lower than the beta of the original, the driving circuit might not be able to fully switch the transistor on, causing the circuit to malfunction (or in a worst case scenario, causing the transistor to overheat).
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Re: Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 6:42 pm

Yep, that's the gist of it. Part numbers come and go, but the driving physics remain the same. Stick to them and you won't have a problem.
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Re: Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 7:16 pm

OK, that's pretty much what I was thinking, go for something with at least same if not higher voltage, current and power handling (I think it was possible an over current / over power that did it in), similar hfe and given that this is an HF oscillator circuit look for similar transition frequency. Just wondering if anyone knew of a standard jelly bean one to throw in there off the top of their heads.

Thanks guys for the thoughts.
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Re: Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 7:56 pm

I see that the part has a complimentary PNP - is this part of a push-pull pair? If so, you might think about replacing both.

Fairchild also make a complementary pair in TO-220, but quite a bit more beefy.
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Re: Replacement for BD230 Transistor?

Postposted on Sun Dec 20, 2009 11:09 pm

Thanks, that FJP5200 is substantially tougher, although it does drop the Ft significantly (30MHz instead of 125MHz), think I'll look for something a bit closer given this is an HF oscillator. It's put me in the right ball park though.

It's just a single NPN, I had drawn everything in xcircuit when I clicked the wrong button and lost it all :-( Will redraw at some point, even if it's just a scan of a hand drawn schematic.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Dec 21, 2009 9:59 am

notfred wrote:Thanks, that FJP5200 is substantially tougher, although it does drop the Ft significantly (30MHz instead of 125MHz), think I'll look for something a bit closer given this is an HF oscillator. It's put me in the right ball park though.

It's just a single NPN, I had drawn everything in xcircuit when I clicked the wrong button and lost it all :-( Will redraw at some point, even if it's just a scan of a hand drawn schematic.


Assuming that you are talking frequency in the 100s of kHz range, the Ft difference should not matter. At 200kHz you are still in a frequency range where most audio output transistors would work just fine. The Fairchild FJP5200 is an exact replacement, physical and electrical, other than Ft. Unfortunately at Ft=3MHz, it may start to matter a bit.

BTW, try Mouser (www.mouser.com). They have a parametric search tool so you can mix and match your settings and see what pops up.

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Re: Replacement for BD230 Transistor?

Postposted on Mon Dec 21, 2009 8:49 pm

Been busy today so not had much chance to do much searching for the transistor but here's the schematicImage
I'm guessing C1 and C2 block the HF going out the inputs. The 16V AC is because that's the standard accessory power so that's why it's half-rectified rather than just running a DC supply. The transformer is a small HF job with a centre tapped primary. The secondary is actually quite thick wire as it has to carry the train motor current. The idea is that as long as the circuit senses the train motor (or I suspect more precisely the train motor suppression capacitor) on the outlet then the HF AC doesn't run. When the wheels go over a bit of dirt then the sense of the motor is lost, the HF runs and the neon lights up to tell you it is doing its stuff. This is accompanied by a reasonable spark from the wheel and continuity is usually re-established. The HF AC is enough to give a burning sensation in the fingers when sorting out a locomotive derailment and probably violates all kinds of modern EMC laws with the track acting like a nice aerial, but this was sold perfectly legally in the UK in the 70s or 80s. Without it, it's a real nuisance trying to keep locomotives that are older then me running, so I hope slapping a new transistor in there is enough to get it going. I do have a scope if I need to tweak the preset to match the new transistor, although it is completely uncalibrated and as it consists of tubes rather than transistors, likely to remain that way - still it should be enough to see if the oscillator is running or not.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Dec 21, 2009 9:30 pm

The way I read it is the primary runs continuously and the resulting secondary (HF) current is blocked by the windings of the locomotive's motor. If the circuit at the wheels is opened, then as soon as the rail's voltage swings the other way an arc is formed, blowing out the dirt/corrosion/mouse poo. Without knowing the resistor values in the primary I can't say for sure, but I'd be very surprised to find that this would operate anywhere close to 3 MHz - there'd be no need and the losses would be needlessly high. The primary probably runs at a few tens to hundreds of kHz, certainly above the threshold of hearing (20kHz).

I imagine this also does a great job of keeping the cat off the tracks. :D

Anyway, the Fairchild part (or almost any other power transistor made in the last 20 years) should be fine.
Last edited by sluggo on Tue Dec 22, 2009 5:56 am, edited 1 time in total.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Dec 21, 2009 11:30 pm

I am in agreement with sluggo here. This thing may be operating at ultrasonic frequencies, but almost certainly not too far into the RF range. The 30 MHz transistor should be fine.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Dec 22, 2009 9:22 pm

notfred wrote:I'm guessing C1 and C2 block the HF going out the inputs. The 16V AC is because that's the standard accessory power so that's why it's half-rectified rather than just running a DC supply.


Actually, as I read this circuit, it is deliberately using the half-wave rectifier on the AC side to pulse the transformer's upper half-winding during the positive cycle, which then sets up and sustains the oscillation cycle during the negative shut-off via flyback. Very likely, the oscillation circuit is significantly overdamped to prevent runaway (and lots of RF interference), and thus relies on each subsequent pulse to maintain the oscillation.

On the supply side, nothing happens while the train is connected because current is flowing through the completed DC supply loop and the transformer acts like an inductor with some nuisance noise being generated by the oscillator winding, which C4 will shunt. If the train loses contact for any reason, the flyback from the inductor field collapse starts the lamp instantly, and the oscillator circuit sustains it by transformer action until the circuit reconnects. Advantage: very fast lamp response, done entirely in analog.

Sluggo's interpretation may be better but I can't see a logical return path for the HF circuit. I think the arcing at the wheels is merely being caused by the inrush current of the motor restarting and possibly a smoothing capacitor recharging. However, I do agree on the frequency issue. I can't see why the oscillator circuit would be operating at more than 15kHz or thereabouts. Even if the circuit concept was swiped from a television flyback driver of that era, it is unlikely to be operating much above 50kHz. Most modern transistor substitutes should be capable of that much.
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Re: Replacement for BD230 Transistor?

Postposted on Sun Jan 17, 2010 9:18 pm

Just want to say thanks to all. Got the FJP5200 fitted, smershed the heatsink to fit back in the box with the transistor a different size and the other way round and it's now back to zapping fingers and maybe some dirt.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 10:11 am

Hi Folks,

I just joined the group!

I have been searching for years for the Relco circuit and found a schematic very much like the one posted by NotFred. I am stumped by the transformer in schematic. What part would I buy or where can I find it? I am just a 57 year old beginner!


Image


Many thanks for your time!

Take care, Joe.
Last edited by jprampolla on Mon Jun 24, 2013 4:35 pm, edited 1 time in total.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 10:56 am

Hi Folks,

I just learned that the transformer used in the schematic I posted

"is a small bell transformer with a 230v primary and an 8 – 10 v secondary. Fitted 'wrong way around' it serves admirably as a step-up transformer. For North American applications you would need a 115v primary with a 4-5 v secondary, again installed the wrong way round.
The principle is quite simple but effective, when larger DC current flows through the secondary winding it saturates the transformer to overwhelm the low current but high frequency AC."

So any suggestions as to an exact part number or source will be greatly appreciated!

Thanks, Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 12:13 pm

jprampolla wrote:Hi Folks,

I just learned that the transformer used in the schematic I posted

"is a small bell transformer with a 230v primary and an 8 – 10 v secondary. Fitted 'wrong way around' it serves admirably as a step-up transformer. For North American applications you would need a 115v primary with a 4-5 v secondary, again installed the wrong way round.

Given the way the transformer is being used in the circuit, either type of transformer should work in any part of the world. It will just be easier to find the 230V one in Europe and the 115V one in North America, since they are more commonly used there.

jprampolla wrote:The principle is quite simple but effective, when larger DC current flows through the secondary winding it saturates the transformer to overwhelm the low current but high frequency AC."

So any suggestions as to an exact part number or source will be greatly appreciated!

Given the above description, this one should work: Triad Magnetics F8X

Mouser has several other similar transformers listed in their catalog, but the F8X was the cheapest one currently in stock. If you're willing to wait a bit you could go with the F7X instead and save a few bucks (it is currently out of stock with a 4 week lead time).

Edit: I am somewhat concerned about the current carrying capabilities of the secondary. If the circuit is used the same way as notfred's, then it needs to be able to pass the entire DC motor current through the secondary (i.e. what would've been the primary if it was wired the right way around). Might actually need to upgrade to a transformer with higher current capabilities to avoid overheating the windings. Given this, I would not use the F7X... get the F8X at least. Maybe notfred can comment.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 12:28 pm

Many, many thanks for the reply and information!!!!!!!!!!!!!!!!!!!!!

After waiting actually many years, a few weeks delay isn't an issue. But, I am unclear as to the center connection on the left side of the transformer in the diagram and which side is low voltage. Looking over these transformer photos I have seen, I usually see only 2 connections on each side.

Thanks, Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 12:35 pm

jprampolla wrote:Many, many thanks for the reply and information!!!!!!!!!!!!!!!!!!!!!

After waiting actually many years, a few weeks delay isn't an issue. But, I am unclear as to the center connection on the left side of the transformer in the diagram and which side is low voltage. Looking over these transformer photos I have seen, I usually see only 2 connections on each side.

Thanks, Take care, Joe.

The secondary (primary in this backwards application) is center tapped (three wires). According to the data sheet there's a third yellow/red wire on that side.

But also please note my edit to my previous post (if you didn't already); there may be some concern regarding whether the one I recommended can handle the required amount of DC current without overheating. Maybe notfred, sluggo, or one of the other usual suspects can weigh in on the issue. I don't know much about model trains, so I don't have a good feel for how much current we're dealing with here.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 12:55 pm

Again, thanks!!!!!!!!!

I should have thought to check the data sheet. Judging from the size of the commercially made units, the Relco and GaugeMaster, whatever is inside those units is very small compared to this F-8X. I know it isn't a good way to judge the rating of a component, but it seems pretty hefty from my uninformed point of view.

If I knew the old Relco units could be repaired -- figured they were sealed in epoxy -- I would just hack one of those. But now I want to build one myself, if I can.

I have been trying to find someone who actually uses the devices who could address some of the adverse effects I have been warmed about. My first electronics project, 25 years ago, was building a high frequency lighting generator to keep train lighting on when DC track power is removed. Although I don't fully understand it, the motor's coils act as a choke to the HF AC. That project was really over my head, but it is still working today and gave me the confidence to dabble in this stuff. That HF AC project didn't use any such transformer, just 2 transistors. I have that schematic if anyone is interested, academically or otherwise.

Looking forward to hearing from anyone who shares this interest!

Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 1:22 pm

jprampolla wrote:Although I don't fully understand it, the motor's coils act as a choke to the HF AC.

Rule of thumb: Inductors (coils) block high frequencies, capacitors block low frequencies and DC. The cutoff frequency (where the degree of blockage becomes significant) depends on the inductance or capacitance value, with higher values corresponding to lower frequencies.

Another way of looking at it is that inductors tend to resist change in the amount of current flowing through them, while capacitors tend to resist change in the voltage across them.
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Re: Replacement for BD230 Transistor?

Postposted on Mon Jun 24, 2013 1:44 pm

just brew it! wrote:Rule of thumb: Inductors (coils) block high frequencies, capacitors block low frequencies and DC. The cutoff frequency (where the degree of blockage becomes significant) depends on the inductance or capacitance value, with higher values corresponding to lower frequencies.Another way of looking at it is that inductors tend to resist change in the amount of current flowing through them, while capacitors tend to resist change in the voltage across them.


Much appreciate the explanation! The best way for me to wrap my head around something is to see it in a practical situation. Thanks!

Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 8:00 am

Was going to try and dig out the Relco last night and check on the transformer but it's packed deep as we have guests coming so the train set room is now the spare bedroom. I do remember the PCB traces for the locomotive power where huge compared to the rest of it.

I think how much current a locomotive draws depends a lot on how modern it is, I've got ones going back to the 1950's that modern controllers can struggle to drive but the good old H&M manages fine. From a bit of Googling that suggests current of 1-2Amps whilst modern motors are 1/10 of that. Having said all that I think it only matters for the Relco type circuit where the train current flows through the transformer. I think in the new circuit posted that it is just attached to the track and the locomotive current is separately attached so no locomotive current through the transformer.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 9:45 am

Many thanks for the information! Please don't bother to look for your Relco unit. I think I have what I need. But I am confused about the circuit I posted as to how it is actually connected to the track. It looks so similar to yours that I wonder if my diagram is incomplete. I might e-mail the gentleman who gave me the additional info about the bell transformer and see if he knows about the proper connection. To me, the similarity at the bell transformer would suggest that it should be connected exactly like the Relco, but I have very little electrical knowledge other than to wear goggles when I fire-up a circuit! :D I am wondering how in this newer design the circuit would know the motor lost connectivity unless it is in series with the DC? But I like to tinker!

I didn't know the Relco units could be repaired or even opened up. I see them on eBay from time to time. I would like to build my own but wonder if the circuit I posted works as well. Perhaps better to just reproduce the Relco.

Last questions, if you have the time, regarding the capacitors in the newer diagram: The one 10nF I assume is nanofarad, but what type should I use (ceramic, mylar), and how important is it that the1000pF (picofarad?) cap be a polystyrene (having trouble finding one -- trying to use only a couple sources for everything)?

Again, thanks everyone, for the kind help! This reminds me of my old Fidonet days.

Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 10:10 am

I was going to say that your circuit should just be wired directly to the track, but that would result in the transformer winding shorting across the track so the locomotive wouldn't run. One way to do it would be with a simple DC blocking cap something like a 0.1uF polyester film rated to a high enough voltage, otherwise it would need to be connected as the Relco is but then I would expect something to stop the AC going back in to the controller.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 10:19 am

I have e-mailed the gentleman who gave me the latest information and I hope he knows. The group that originally designed and published the circuit doesn't provide assistance to non-members. I got the diagram from a FDF from another group and it appears the images where from a PowerPoint presentation at a model train symposium, perhaps incomplete.

As soon as find out, I will post it here.

Thanks! Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 10:25 am

Small transformers can be built from scratch or rewound with sufficient knowledge, materials, and patience, but it's not a job for a novice. Provided you can find an off-the-shelf substitute, there's really no reason to rewind a small transformer unless you really, really enjoy doing it.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 10:44 am

I was wondering if a 5 volt wall wart could be opened and that coil be used in the project, but opening that sealed case is almost impossible. I have a few that are screwed together, but most are glued/fused shut. But I don't think I would ever try to make my own.

Thanks, Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 11:01 am

jprampolla wrote:I was wondering if a 5 volt wall wart could be opened and that coil be used in the project, but opening that sealed case is almost impossible. I have a few that are screwed together, but most are glued/fused shut.

Use a small handsaw or steel file and work slowly. Just as the tool starts to break through the plastic, stop. Do the same thing on all four sides, then use some other tool to carefully pry the case apart. Pretty much all you should find in there is a thermal fuse, a transformer, and (if DC output) a small rectifer circuit.

An off-the-shelf bell transformer is the most reliable option, though.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 11:22 am

I wouldn't try to cannibalize a wall wart for this. If it is an old school linear regulated DC wall wart, then it is going to have a primary that is somewhat higher voltage than you want. If it is a newer one (switching regulator) then there won't be a traditional step-down transformer in there at all.

I suppose if you have a 5V AC wall wart sitting around that might be of some use...
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 8:18 pm

Hi Folks,

I heard from the gentleman who gave me the a clearer diagram of the circuit and the bell transformer information. I quickly drew the correct way to hook this up. I have to look at the Relco directions to see if you use the direction switch on the powerpack or a separate polarity reversing switch. Guess it doesn't matter which way the DC flows through the bell transformer.
Image
So now it is just a matter of finding the capacitors. If I make the circuit myself, I can always replace a component if one fails. Would like to make 2 devices.

It is over my head, but if the device could be modified to have AC on the rails, then that would great for the older stuff that doesn't have any circuits or diodes.

When I get it all together, I'll do a little video of it in operation, perhaps catch a few sparks flying. :lol:

Thanks for all the help!!!!!!!!!!!! I may need a little advice as a build it.

Take care, Joe.
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Re: Replacement for BD230 Transistor?

Postposted on Tue Jun 25, 2013 8:23 pm

Regarding the wall wart -- I may try to cut open one, but not sure if would have the center tap like the bell transformer. Thanks for the tips on opening one up!
Take care, Joe.

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