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Ruskie

Thu Jan 24 2013, 07:17PM

Registered Member #9290 Joined: Sat Jan 05 2013, 03:42PM
Location:
Posts: 60

klugesmith

Fri Jan 25 2013, 12:37AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Oh yes, good old "ASCII" (fixed pitch font) images.
A chance to propose, without starting a new thread,
a drawing style that makes schematics more compact and easier to draw.
(Anyone know of a GUI drawing program for ASCII schematics?)

Here's the original, thanks to Sam Goldwasser's Repairfaq site:

+Vcc     Q1   +----------------+
     o           |                 )::
     |       B |/ C                )::
     |  +------|    2N3055         )::
     |  |      |\ E           5 T  ):: +------|>|----------o  +HV
     |  |        |                 )::(   HV Diode, usually
     |  |       -_-                )::(    built in.
     |  |                          )::(
     +--|-------------------------+ ::(
     |  |   Q2  _-_                )::(
     |  |        |                 )::( Secondary (HV) winding,
     |  |    B |/ E           5 T  )::(  intact.
     |  |  ----|    2N3055         )::(
     |  |  |   |\ C                )::(
     |  |  |     |                 )::(
     |  |  |     +----------------+ ::(
     |  |  |                        ::(
     |  |  -----------------------+ :: +------------------o  -HV
     |  |                     2 T  )::
     |  |               +---------+ ::
     |  |               |     2 T  ):: T1 - Flyback transformer from B/W or
     |  +-------------------------+         color TV or computer monitor.
     |                  |
     |            R1    |    R2
     +----------/\/\/\--+--/\/\/\--+
                  110        27   _|_
                  5 W        5 W   -

Here's the alternate, with more compactly rendered Q's and R's:

+Vcc     Q1   +----------------+
     o           |                 )::
     |           C                 )::
     |  +-------B   2N3055         )::
     |  |        E            5 T  ):: +------->|---------o  +HV
     |  |        |                 )::(   HV Diode, usually
     |  |       -_-                )::(    built in.
     |  |                          )::(
     +--|-------------------------+ ::(
     |  |   Q2  _-_                )::(
     |  |        |                 )::( Secondary (HV) winding,
     |  |        E            5 T  )::(  intact.
     |  |  -----B   2N3055         )::(
     |  |  |     C                 )::(
     |  |  |     |                 )::(
     |  |  |     +----------------+ ::(
     |  |  |                        ::(
     |  |  -----------------------+ :: +------------------o  -HV
     |  |                     2 T  )::
     |  |               +---------+ ::
     |  |               |     2 T  ):: T1 - Flyback transformer from B/W or
     |  +-------------------------+         color TV or computer monitor.
     |                  |
     |                  |   
     +------------R1----+----R2----+
                  110        27   _|_
                  5 W        5 W   -

Comments?

By the way, I regularly encourage noobs always to put reference designators into their schematics.
Then discussions can refer to "R1" instead of "The leftmost 110 ohm resistor".
And if you ever change the component value in the schematic,
it won't break references to that location in previous discussions.

GrantX

Fri Jan 25 2013, 05:01AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

I've tried building two of these 3055 drivers (a single transistor, then the double transistors) out of boredom, and had eventual failures with both. Never had an issue with live PSU, but I was using an iron core transformer, not an ATX supply. I'm not sure if the eventual failures is related to circuit design, or the transistors used, but everything I've read about this circuit is bad.

Shrad

Fri Jan 25 2013, 08:23AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

three is a difference between old and new 2N3055 transistors

the new ones are epitaxial designs, which suffer excessively in this regime, while the old ones are rock solid (new as after year 2000 or something, don't know)

GrantX

Fri Jan 25 2013, 09:11AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Shrad wrote ...

three is a difference between old and new 2N3055 transistors

the new ones are epitaxial designs, which suffer excessively in this regime, while the old ones are rock solid (new as after year 2000 or something, don't know)

That's probably the issue I had, I made these drivers early last year sometime, after snatching a few 2N3055's from school. I grabbed a random bunch of both metal case and plastic package transistors from the supply closet. They all looked new, and tested good prior to using them, however it's impossible to know whether they'd been abused previously.

Ash Small

Fri Jan 25 2013, 09:38AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

There are also several different spec. 2N3055's, with designations like E, H and G, off the top of my head. One will work at higher frequencies (3MHz), One has higher current rating, one has higher voltage, or something like that (I'll check later and update this post). Also, there are differences between manufacturers, and even different factories owned by the same manufacturer.

I obtained half a dozen Motorolla ones from the Mexico factory in 2001, which have so far been virtually indestructible. (I blew one when running a flyback from it with no heatsink).

I started a thread somewhere about testing them to destruction, to compare the various different sources, etc. for them, but need to finish building a ~300 watt variable resistor I'm working on to use as a test load. I will then hopefully be able to ascertain which ones are most reliable.

@Ruskie: Where did you obtain yours? What make are they? and are they marked with the country of origin?

Shrad

Fri Jan 25 2013, 11:32AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

mosfet royer

Ash Small

Fri Jan 25 2013, 12:40PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

You can damp the voltage spikes with snubbers accross the 2N3055's. I think you'd need a capacitor and diode in series, with the diode connected to the collector, and capacitor connected to the emitter, with a resistor in parallel with the capacitor. I can't remember offhand what values, though.

(Maybe ~250-500uF, and at least 1kOhm, and a fast diode, maybe someone else can suggest some values?)

Steve Conner

Fri Jan 25 2013, 01:07PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Shrad, more like 1980 than 2000

Shrad

Fri Jan 25 2013, 01:40PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

yeah I think so, I don't know why I felt 80's were a bit early for the technological change, and 90's too. I guess I was thinking about scavenging rate... by the 2000's there were not much original designs left to scavenge in generic appliance

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