Osborne Vixen - Zenith 7" display t-shooting issues
drlegendre at gmail.com
Fri Nov 7 11:41:13 CST 2014
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
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
> 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.
>> 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.
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