7 Nov
2014
7 Nov
'14
9:41 a.m.
Say, one quick question... this has been bugging me.
Exactly how is it that one little TO-220 device can have a Pt (total power
dissipated, right?) of like 75W, when a plain 75W power resistor is
physically many, many times larger and more massive? Does that Pt imply
some serious heat-sinking or something?
And if so, then why aren't all TO-220 power devices in the same range? Why
would some be rated as low as 5-10W, if it's really a matter of sufficient
cooling?
On Fri, Nov 7, 2014 at 11:35 AM, drlegendre . <drlegendre at gmail.com> wrote:
Chuck & All,
Hey, now +that's+ interesting.. I did look at the data for the MJE13007
and while I'm not exactly up-to-speed on solid state stuff, the specs seem
to compare very well with the generic NTE 379 we've been discussing. And
much like the NTE, suggested apps include SMPS, inverters and deflection
circuits (I assume when they state the latter, "analog CRT" is implied?).
Likewise, the PHE 13005 also compares fairly well, though it seems to have
somewhat lower current ratings, both collector and base. The data
specifies "lighting ballast" and makes no mention of SMPS or deflection
service, though. I'm going to make a guess that it's not quite as fast a
switching part as the others.. or maybe the 'on' resistance is a bit
high-ish? But all three devices discussed have the same low beta, 8-10 min
/ 30-40 max.
Naturally, I binned half a dozen bad CFLs only a week ago..
So Chuck, if it were yours, I take it that you'd throw a 13007 at it
without a whole lot of further thought? It's looking very appealing, being
I can buy 10 of them for about $4.50 including shipping, and they clearly
have lots of other uses (like repairing SMPSUs and other small computer
monitors).
On Fri, Nov 7, 2014 at 1:30 AM, Chuck Guzis <cclist at sydex.com> wrote:
Well, Tony may have a problem with this one, but
SMPSU transistors and
HOTs do share a lot of common characterists. For example, instead of the
NTE unit, consider the MJE13007, a old Motorola design that saw use in both
SMPSUs as well as HOTs. Common as dirt.
eBay, for example, has a BIN for 10 of them for less than $6 shipped.
(item 140811430465).
Compare the datasheets for yourself.
--CHuck
P.S. I have a terrible, but relevant confession--I don't like to throw
things out as long as they contain useful parts. For example, I accumulate
bad CFLs then remove the lamp, extricate the electronics PCB, line them up
out of doors over a metal pail and apply a heat gun to the trace side of
the little pcb until the solder softens. Grab with pliers and bang each
one against the side of the pail to allow components to drop out and then
move on.
Right now, I'm holding what fell out of the innards of a 20W CFL base.
There are several power transistors with heat sinks, several inductors,
diodes (of the 1N400x type), miscellaneous capacitors, etc. What makes
this germane to the topic under discussion is that the base contained two
NXP PHE 13005 transistors. Compare the datasheet with your NTE one.
Like I said, common as dirt.