K
Kasper
- Jan 1, 1970
- 0
Eeyore said:You're 100% confident no diodes have gone open circuit ?
99.9 but i will happily test again tommorow
Rapzak
Eeyore said:You're 100% confident no diodes have gone open circuit ?
Kasper said:If they have found the source to the problem, this could be the same
problem, so i don't see that as stupid.
This is also because that i believe it is not a common way the transistoer
is destroyed
do to the functionality it has afterwards.
that
helps much.
Your approach to the finding of the fault is not very scientific. Humans
once
examined the entrails of dead animal to foretell the future. Examining
dead
transistors is little better.
If you have read what i have writtenm you have nottiched the layers notUh ? The functionality it has afterwards is NONE.
No 18V 1276 Ohm for 1 and the 2 other is 1620 Ohm.
Also the software locks for not activating all 3 releays at once.
Then we could discuss just when the uC starts up, all 3 + boost is
activated... hmm...
The allowed peak current is 200mA.
I would *not* use such wimpy parts as those in this application. Put
MMBT4403 or MMBT2907 parts in there (same footprint, maybe same pinout
(?)) and I'll bet your problems go away, if they are not diode
related. There is negligible price difference. Might be a good idea to
increase the base current on the PNP a bit too, like up to 5mA or
10mA. It's only on for a brief period.
BTW, what prevents the relays and C10 from ringing? Did you try a zener to
ground so at least it can't swing above safe limits for TR8 or below
ground? It might be worthwhile to hang a fast digital scope on TR8's
collector and trigger that with a relay command. It could yield an ugly
surprise.
No 18V 1276 Ohm for 1 and the 2 other is 1620 Ohm.
Also the software locks for not activating all 3 releays at once.
Then we could discuss just when the uC starts up, all 3 + boost is
activated... hmm...
The allowed peak current is 200mA.
The biggest problem with that are we have seen problems back to last year,
so the problem is made over several production lots.
But we have ofcause checked the diodes on several bad units, and they
measured correctly.
Kasper said:
Just not easy to see anything on the equipment i have availible for this
point.
Kasper said:If you have read what i have writtenm you have nottiched the layers not
seems destroyd due to even when the impedance between C and E is arround
250ohm, it will be lower when there is a base/emitter current. And also both
base/emitter and base/collector "diodes" are present.
That report says BC856, not BC857. Hmm...
Take a DSO. It doesn't have to be faster than 100MSPS for this job. Look
at the collector node while relays are switching (trigger on that). Try
with all relays since you wrote that there are at least two types used. If
you guys don't have a DSO then borrow it, and buy one as soon as possible.
I don't know which country you are in but it looks like Europe. In that
case Farnell has some pretty good deals, I even bought one there here from
the US.
Do you have a datasheet for that part? *With* an SOA curve?
Spehro said:I would *not* use such wimpy parts as those in this application. Put
MMBT4403 or MMBT2907 parts in there
Joerg said:That report says BC856, not BC857. Hmm...
Kasper said:That is an mistake, it is BC556, sorry for that.
Kasper said:Yes, this point also came to my mind after i have used a litle time with
spice.
So that i defentlig will try tommorow to measure
(and yes, Kasper is my real name )
Kasper said:
Offhand, it does not appear that there is anything to keep the collector of
TR8 from going to an arbitrarily large negative voltage.
Tam
Tam/WB2TT said:Offhand, it does not appear that there is anything to keep the collector of
TR8 from going to an arbitrarily large negative voltage.