Have you ever thought of using an opto isolator?
I use a LCA710. Rated for 2 amps dc and can handle 24 volts with no problem.
I use a 680 ohm resistor on the input from the basicx.
There are other opto isolators that are cheaper too.

Chris wrote:
I have to control a few 24v light bulbs using pins on the BX24. I'm
wondering if there is a transistor I can use to power the bulbs
directly . The bulbs draw 208ma.

---------------------------------
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The best is still what Tom said by using a FET instead
of a transistor.
Wim

--- r...@aol.com wrote:

>
> Hi,
> Maybe the lamp is pulling more current than
> 208ma. Normally the lamp resistance is low when is
> cold and them goes high when
> is turn on. Are you using plastic 2N2222 or metal?
> ?They come in metal type TO-18. This will worked
> better than the
> plastic and the rating is higher than the plastic.
> Worst case then use a darlighton switching transistor
> like the TIP121. This will handling anything that you
> want to turn on relays/lamps/selenoids. The bad thing
> it is a TO220 case.
>
> rosarite
>
>
> -----Original Message-----
> From: Chris
> To: b...
> Sent: Tue, 12 Jun 2007 5:36 pm
> Subject: [BasicX] Re: driving a 24v relay/transistor
>
>
>
>
>
> Ok, I've got the circuit working with 3 2N2222
> transistors driving
>
> the 5W incandescent bulbs, one at a time. While it's
> working
>
> perfectly, the transistors are getting hot (155
> degrees or so) and
>
> they're getting more airflow than they will in
> service. I guess I need
>
> a transistor equipped with a heatsink, or a more
> efficient one - or a
>
> set of relays.
>
>
>
>
>
>
>
>
>
>
________________________________________________________________________
> AOL now offers free email to everyone. Find out more
> about what's free from AOL at AOL.com.
>
Wim Nijntjes
Oranjekanaal 38 NZ
9415TP Hijken
The Netherlands

____________________________________________________________________________________
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Hi,
Maybe the lamp is pulling more current than
208ma. Normally the lamp resistance is low when is cold and them goes high when
is turn on. Are you using plastic 2N2222 or metal? ?They come in metal type TO-18. This will worked better than the
plastic and the rating is higher than the plastic.
Worst case then use a darlighton switching transistor like the TIP121. This will handling anything that you want to turn on relays/lamps/selenoids. The bad thing it is a TO220 case.

rosarite

-----Original Message-----
From: Chris
To: b...
Sent: Tue, 12 Jun 2007 5:36 pm
Subject: [BasicX] Re: driving a 24v relay/transistor

Ok, I've got the circuit working with 3 2N2222 transistors driving

the 5W incandescent bulbs, one at a time. While it's working

perfectly, the transistors are getting hot (155 degrees or so) and

they're getting more airflow than they will in service. I guess I need

a transistor equipped with a heatsink, or a more efficient one - or a

set of relays.

________________________________________________________________________
AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com.

> ... hot (155 degrees or so)...

A 2N2222 might be marginal for your load, Chris; you can determine its
dissipation to be certain. When a lamp is on, measure the voltage
between the collector and emitter and multiply that by the current (you
said 208mA); the product is the dissipation in Watts. A 2N2222 can
dissipate something like 500mW to a Watt, but it will be hot to the touch.

You should be driving the base with 20mA or so to guarantee that the
transistor is saturated; if that is so, you should see something like a
volt between the collector and emitter and the dissipation will be
~200mW. That will still make a TO-92 package pretty warm, but you can
snap a small heatsink on it and probably do fine.

You might consider some of the other choices, and a Supertex VN2222 will
drop in place of your 2N2222 and only dissipate ~40mW.
Tom

Ok, I've got the circuit working with 3 2N2222 transistors driving
the 5W incandescent bulbs, one at a time. While it's working
perfectly, the transistors are getting hot (155 degrees or so) and
they're getting more airflow than they will in service. I guess I need
a transistor equipped with a heatsink, or a more efficient one - or a
set of relays.

I was on a project where we used TIP 120 I haven't had the chance to really look at how the outputs are set up, on the chip you are using, but we were using a 2n2222 tied to a tip 120 the transistor is rated at about 8 amps. The 2n2222 was tied to a CMOS logic output so I think if the BasicX goes high it would connect to the base of the 2n2222 I think through a 20k and the collector to the + supply, and the emitter would feed a 2k to ground and I think a 3k to the base of the TIP 120. The emitter of the TIP 120 is connected to ground and the load is connected to the collector. When the gate goes high the 2n2222 follows the logic gate and causes the TIP 120 to ground the load (in this case the ground side of the bulb would be the switched side). In your case the 2n2222 could do the job, you could just put the bulb in parralell to the 2k. This was a few years ago so if you try this, I would do the math so the parts are'nt being overloaded. It also would be good to
put filter caps so that the circuit would only run on near DC, That is to make sure no high frequency stuff would be amplified. The TIP 120 is set up to drive coils it has a diode in the output to stop spike from coming back into the transistor and zapping it. This info may need some verification and is intended as a help drive loads. I know one thing, that bulbs increase in resistance as they warm up so when they are cold they read one resistance and when on they read another value.

----- Original Message ----
From: "n...@ihug.co.nz"
To: b...
Sent: Sunday, June 10, 2007 6:44:10 PM
Subject: Re: [BasicX] driving a 24v relay/transistor

BC337 or a power FET( better)

Chris wrote:

> I have to control a few 24v light bulbs using pins on the BX24. I'm

> wondering if there is a transistor I can use to power the bulbs

> directly . The bulbs draw 208ma.

>

>

>

>----------- --------- --------- --------- --------- --------- --

>

> 1:39 p.m.

>

>

UCN5821 also does this job in 16pin DIP

PFiX Controls wrote:

> Chris,
>
> You can use a TPIC6273, 20-pin DIP, 8-channel driver, continuously
> drives 250mA per output with 1.5Amp pulsed current.
> You can even buy them from Digi-Key.
>
> Chuck
> ----- Original Message -----
> From: njepsen@ihug. co.nz
> To: basicx@yahoogroups. com
> Sent: Sunday, June 10, 2007 8:44 PM
> Subject: Re: [BasicX] driving a 24v relay/transistor
>
> BC337 or a power FET( better)
>
> Chris wrote:
>
> > I have to control a few 24v light bulbs using pins on the BX24. I'm
> > wondering if there is a transistor I can use to power the bulbs
> > directly . The bulbs draw 208ma.
> >
> >
> >
> >----------- --------- --------- --------- --------- --------- --
> >
> > 1:39 p.m.
>
>

Hi,
Normally for that type of application?is good
to use a switching transistor. I recommend you the 2N2222 that is a switching
transistor 800ma collector current, 40 volt on a TO18 or TO92 case.

Used a 10k resistor from the BX pin out to the base of the transistor.
?
rosarite

-----Original Message-----
From: Chris
To: b...
Sent: Mon, 11 Jun 2007 7:55 pm
Subject: [BasicX] driving a 24v relay/transistor

I have to control a few 24v light bulbs using pins on the BX24. I'm

wondering if there is a transistor I can use to power the bulbs

directly . The bulbs draw 208ma.

________________________________________________________________________
AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com.

Chris,

You can use a TPIC6273, 20-pin DIP, 8-channel driver, continuously drives 250mA per output with 1.5Amp pulsed current.
You can even buy them from Digi-Key.

Chuck
----- Original Message -----
From: n...@ihug.co.nz
To: b...
Sent: Sunday, June 10, 2007 8:44 PM
Subject: Re: [BasicX] driving a 24v relay/transistor
BC337 or a power FET( better)

Chris wrote:

> I have to control a few 24v light bulbs using pins on the BX24. I'm
> wondering if there is a transistor I can use to power the bulbs
> directly . The bulbs draw 208ma.
>
>
>
>----------------------
>
> 1:39 p.m.
>
>