EMRFD Message Archive 389
Message Date From Subject 389 2007-01-29 18:03:33 Nick What's better than a TIP31?
one) I will keep the OEM to myself so as not to get in any trouble.
The transmitter uses a TIP 31 as the AF amp and it tends to run hot
most of the time. I have looked at an MJ21194 as a replacment. Will
this work and is there anything else that someone might reommend as a
replacement for the TIP31? I have solved most of the issues by using a
regulated power supply, a better heat sink, and a tiny cooling fan
monted inside the transmitter case. Like most others here, I am just
trying to research any improvment that I can make!
Thanks!
Nick391 2007-01-29 21:26:05 jim.scott@scottel... Re: What's better than a TIP31?
Sounds like Class A, so any device will dissipate the *same* worst case power while idling (VxI). To cool this TO-220
down, get the heat out of there, more heatsink and/or fan.
If Class B - reduce the DC base bias to almost off. Crossover distortion will rise some, but I doubt you will notice it -
it isn't Hi-Fi :-)
Jim Scott
WB0IYC392 2007-01-30 07:28:47 D Re: What's better than a TIP31? 393 2007-01-30 09:58:58 Nick Moody Re: What's better than a TIP31?
is in. I was thinking of mounting it externally. The
leads would only be a few inches long.
Thanks to everyone for your replies.
Nick
394 2007-01-30 10:06:39 Andy Re: What's better than a TIP31?
> > worst case power while idling (VxI). To cool this TO-220
> > down, get the heat out of there, more heatsink and/or fan.
>
> Or, depending upon how flexible the design is, switch to a
> transistor in a TO-3 case, which has a lower thermal resistance
> and can dissipate more heat to a larger heat sink.
thermal resistance from case to ambient. Get the heat away from the case.
If you don't have that (i.e., a better heatsink or more contact with one),
then lower thermal resistance (junction to case) doesn't do anything except
make the case get hot faster!
It is true that a bigger case such as TO-3 has more surface area so a little
less case-to-ambient thermal resistance. But the key is heatsink.
Andy396 2007-01-30 13:17:45 jim.scott@scottel... Re: What's better than a TIP31?
TO-3 I don't know of it, however TO-66 might be available. Still, if you can achieve a larger radiating surface area with
moving air, that is the quick and dirty fix. Moving it outside the case esp. if cooler will help. It is all about temp
difference and getting the heat away with some sort of sink. I just looked in a Motorola data book, and this TIP-31 in a
TO-220 case kept at 25 degrees Centigrade has a max of 40W Pd.
There is a TIP41/TIP42 series that you might consider to substitute. It has a higher current rating, and the current gain
is actually higher. It is more robust, but the parms vary somewhat. Don't forget to match suffix (none=40V, A=60V,
B=80V, C=100V). If there is nothing too special about this amp and it is operating at low frequencies, you might try a
sub TIP41 vs TIP31. However, the heat generated will still be the same.
Is this in a mfr. unit? If so, one might ask why the circuit runs so hot, esp. since the mfr. did not apparently see it
as a problem.
Good luck!
73
Jim Scott
WB0IYC
>
> The TO-3 case is what the other one that I mentioned
> is in. I was thinking of mounting it externally. The
> leads would only be a few inches long.
>
> Thanks to everyone for your replies.
> Nick
>
>400 2007-01-30 16:34:05 Nick Moody Re: What's better than a TIP31?
Firts off, although I am an "ok" tech, I am not
much of an engineer so I have started the learn by
doing approach. And yes, it is in a manufactured unit
and they do know about the problem and have told many
users that "it is ok" , and "that's just how it is". I
have solved some of the issues just by adding a
regulated power supply. They sell the unit with a
Jameco wall wart that is supposed to be 15VDC but I
have seen it go upwards of 20 to 25VDC. This TIP31C
gets hot enough to scorch the board. I have started
playing around with bias voltage settings to see what
effect that has. I would scan and share part of the
schem. I just don't want to get into a bashing of a
product. I am honestly trying to improve on their
design because otherwise it is a solid product and I
have sold a t409 2007-01-31 06:40:36 D Re: What's better than a TIP31? 411 2007-01-31 07:55:41 Andy Re: What's better than a TIP31?
> and they do know about the problem and have told many
> users that "it is ok" , and "that's just how it is".
feels pretty hot to the touch, sometimes people are surprised but it might
really be OK.
On the other hand I fixed a piece of broadcast equipment that had a 1/4 watt
resistor dissipating just over 1/2 watt. Somebody forgot to do a simple
calculation. (Nobody's perfect!) By a year later the color codes were
missing ... but the resistor still worked.
Just remember, if the TIP41 is in the same case as the TIP31, it will get
just as hot. The only ways to make it cooler are (1) reduce the V*I, or (2)
move the heat away faster, which requires different mechanics or airflow.
Having a higher current rating doesn't change anything.
Andy418 2007-01-31 13:45:33 jim.scott@scottel... Re: What's better than a TIP31?
Exactly. :-)
Although the TIP41 is more robust and capable of 65W Pd at a case temp of 25 degrees Centigrade, the pkg will still be
dissipating the same heat *regardless* of transistor chosen.
> On the other hand I fixed a piece of broadcast equipment that had a 1/4 wattGood luck,
> resistor dissipating just over 1/2 watt. Somebody forgot to do a simple
> calculation. (Nobody's perfect!) By a year later the color codes were
> missing ... but the resistor still worked.
>
> Just remember, if the TIP41 is in the same case as the TIP31, it will get
> just as hot. The only ways to make it cooler are (1) reduce the V*I, or (2)
> move the heat away faster, which requires different mechanics or airflow.
> Having a higher current rating doesn't change anything.
JIm Scott