[TechAssist] Re: Horizontal output overheating.
- From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Wed, 18 Dec 2002 20:22:18 -0500
To keep the circuit simple, I would think that the transistors would have to
be matched sets, matched for a bunch of parameters, and thermally coupled
for temperature compensation. Also the drive circuit would have to have
plenty of drive current and voltage available to drive the pair on and off
to the minimum switching times. With seperate drive sources and emitter
resistors, the matching is less critical. That requires more parts and
sacrifices some efficiency.
Obviously these things have been done in TVs in the past so it is possible.
I have a Diehl MK V scanner, used to sub for the HOT in troubleshooting,
which claims to have a bulletproof HOT. Peeking in to the heatsink, I do see
a pair of transistors in TO-3 cases.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "Vilhelm Boor" <villyboor@xxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>; <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, December 18, 2002 9:42 AM
Subject: [TechAssist] Re: Horizontal output overheating.
>
> Villy boor
> Boorelec Durban
> Mr Silverman I thank you for your reply, it is the reply I believed
correct from the start, the only issue I would have with it is this. Let us
assume I require a 10A output and use 2 by 8A devices. The impedance
matching we both know is not an issue as we have actually improved that.
The timing issue someone raised requires there to be a fault, this is not a
repair to camoflage a fault so again a non issue. Now we have produced a 16A
device which supplies 10A. Regardless of the slight imbalance which must
exist it is doubtful if 1 transistor will draw enough current to "hog" the
current and get hot enough to fail, I as yet have not had a response which
makes me less likely to use this rather than the rip off manufacturers
transistor.
> --
>
> On Tue, 17 Dec 2002 16:25:53
> J Silverman wrote:
> >
> >We used to design and manufacture 300 amp chopper drives for electric
> >vehicles. We used six 100 amp transistors in parallel. We had to use
emitter
> >resistors to get the current to share. We used a seperate driver for each
> >transistor. The base - emitter voltage drop of a transistor decreases
with
> >heat, so the hotter transistor would tend to hog all the drive current if
> >the bases were in parallel and we used no emitter resistors.
> >Jerry Silverman
> >Greentron Inc
> >4 Newland Ave
> >Greenville SC 29609
> >864 232 3889
> >Fax 271 2080
> >mailto:greentron@xxxxxxx
> >----- Original Message -----
> >From: "Al Gutz" <alg@xxxxxxxxxxx>
> >To: <techassist@xxxxxxxxxxxxx>
> >Sent: Monday, December 16, 2002 10:27 PM
> >Subject: [TechAssist] Re: Horizontal output overheating.
> >
> >
> >>
> >> Paralleling transistors is not a problem, if one starts to conduct more
> >> it gets hotter and its effective resistance increases causing the other
> >> cooler transistor which has a lower effective resistance to pickup more
> >> of the load. A point of balance is reached. I have worked on high power
> >> broadcast applications where you may have many transistors or mosfets
in
> >> parallel. When you are looking for outputs of up to 50 Kwatts you don't
> >> do it with one transistor. This aside I don't know if I would do it
with
> >> a HOT. You can safely sub these provided you pay attention to switching
> >> times and transition times, max CE volts, Max BE volts and total Pout.
> >> If you sub and keep transition/switch times the same its no problem to
> >> increase the Imax ans Pout. ei 2SD1879, 1880, 1881 all have same specs
> >> except for Imax and Pout.
> >>
> >> Al G
> >> Al's TV-Electronics
> >> Pembroke Ont.
> >> Canada
> >>
> >> Gary McCartney wrote:
> >> >
> >> > I always read that using two semiconductors in parallel will cause
the
> >> > one of them to hog all the current, unless you install a small
current
> >> > limiting resistor (perhaps 0.01 ohm or there abouts) in the paths of
the
> >> > 2 emitters. Has anyone else heard of this?
> >> >
> >> > Gary McCartney
> >> >
> >> > McCartney Electronics
> >> > 7134 Fife Rd, RR 7
> >> > Guelph Ontario Canada N1H 6J4
> >> > Fax: (519)821-1530
> >> > email: gary (at) number63.ca
> >> >
> >> > teltek2 wrote:
> >> > >
> >> > > I agree...using 2 will put you into price range of OEM.
> >> > >
> >> > > Fix the fault..install OEM part, ship it. Done.
> >> > >
> >> > > -Ed-
> >> > > Tel-Tek Electronics
> >> > > Ontario-Canada
> >> > >
> >> > > teltek2@xxxxxxxxxxxx
> >> > > ----- Original Message -----
> >> > > From: <HSWAD@xxxxxxx>
> >> > > To: <techassist@xxxxxxxxxxxxx>
> >> > > Sent: Monday, December 16, 2002 9:09 AM
> >> > > Subject: [TechAssist] Re: Horizontal output overheating.
> >> > >
> >> > > > Wouldn't it be about the same price to replace with the correct
> >part?
> >> > > > Modifications put you in a responsible position . Hollis Bates,
> >field
> >> > > > engineer-retired In a message dated
12/16/02
> >5:13:25
> >> > > AM
> >> > > > Eastern Standard Time, villyboor@xxxxxxxxx writes:
> >> > > >
> >> > > >
> >> > > > > Subj:[TechAssist] Re: Horizontal output overheating.
> >> > > > > Date:12/16/02 5:13:25 AM Eastern Standard Time
> >> > > > > From:<A
HREF="mailto:villyboor@xxxxxxxxx";>villyboor@xxxxxxxxx</A>
> >> > > > > Reply-to:<A
> >> > > HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>
> >> > > > > To:<A
> >> > >
HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>,
> ><A
> >> > > HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>
> >> > > > > Sent from the Internet
> >> > > > >
> >> > > > >
> >> > > > >
> >> > > > >
> >> > > > > Villy Boor
> >> > > > > Boorelec Durban
> >> > > > > --
> >> > > > > Perhaps I am a wee bit off the topic but I have been finding
> >many TVs
> >> > > > > with troubles after the horizontal output has been changed.
What I
> >find
> >> > > is
> >> > > > > if you get the expensive manufacturers transistor all is well,
the
> >> > > generic
> >> > > > > fails. My tip here is use 2, parallel them up and there is no
need
> >to
> >> > > > > increase heat sinks as there will be less heat, the input
> >inpedance
> >> > > drops
> >> > > > > so it is more stable, as yet after 2 years on sets where no
faults
> >were
> >> > > > > found and the transistor failed, I have had no returns. Your
> >comments
> >> > > > > welcomed, Villy.
> >> > > > > On Sun, 15 Dec 2002 08:13:25
> >> > > > > Paul Medvetz wrote:
> >> > > > > >We have a Sony KV-32S35 , Set came in dead with shorted
> >horiz.out,
> >> > > > > reg.Q601 and Q602, Replaced Q601,Q602, Q502,
VDR601,R607,C502.Set
> >now
> >> > > plays
> >> > > > > but Q601,Q602, get very hot just after three minutes,This set
was
> >in
> >> > > shop
> >> > > > > two months ago for shorted flyback and horiz.out
transistor.Don't
> >want
> >> > > to
> >> > > > > leave it on any longer I know it will short again,Also I did go
> >over
> >> > > > > connections in horiz. thanks in advance for any help.
> >> > > > > >
> >> > > > > >Paul Medvetz
> >> > > > > >TV- Service-CO.
> >> > > > > >Hazleton,Pa. 18202
> >> > > > > >paulcho@xxxxxxxx
> >> > > > > >
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