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obsolete transistor replacement

D

Dave

Jan 1, 1970
0
I've identified a bad transistor in the power supply of an audio component,
circa 1981. It's a 2SB527 PNP transistor... I had a bit of a look around on
the net and didn't find any quick easy sources. This transistor's sole
function is to convert -26VDC coming off one side of a bridge rectifier
to -13 volts. It's wired up as follows, and I apologize for not being more
skilled in ascii art or I'd try to draw it.

The collector is the -26VDC input. It is connected to ground via a 100uF
cap.
The emitter is the -13VDC output. It is connected to ground via a 10uF cap.
The base is connected to a series 470-ohm resistor, then a parallel 10uF cap
(to ground), then a parallel zener diode (to ground), then a 5.6K-ohm
resistor, then to the collector.

My question is thus: if my downstream components can get by with -15VDC,
can I just substitute a 7915 15VDC negative voltage regulator? There are no
feedback connections from any other part of my circuit to this transistor,
it's output voltage should not vary under normal conditions. And, by freak
coincidence, the pinout of the regulator matches my circuit perfectly, it'd
be a straight swap and removing a couple of resistors. And perhaps most
importantly, I have one.
 
D

David C. Partridge

Jan 1, 1970
0
I'd think that any PNP power xistor with an adequate voltage rating would
do - this is just a pass xistor wired as an EF isn't it?

David
 
D

Dave

Jan 1, 1970
0
David C. Partridge said:
I'd think that any PNP power xistor with an adequate voltage rating would
do - this is just a pass xistor wired as an EF isn't it?

David
I know very little of transistors other than their basic function, so I
don't know the answer to your question above.

As I noted, it's being used to (down)-regulate negative DC voltage. What
might the reason have been to opt for this transistor over a regulator?
There is a +5VDC regulator right next door in the same circuit.

Can I use the regulator in place of the transistor?
 
D

Dave D

Jan 1, 1970
0
Dave said:
I know very little of transistors other than their basic function, so I
don't know the answer to your question above.

As I noted, it's being used to (down)-regulate negative DC voltage. What
might the reason have been to opt for this transistor over a regulator?
There is a +5VDC regulator right next door in the same circuit.

Can I use the regulator in place of the transistor?

Maybe, maybe not. The 2V difference probably isn't critical, but we don't
know how much current is being drawn. The 7815 is only good for around an
amp with a big heatsink, (some variants 1.5 A), the 2SB527 is good for 2A.
You could try one and measure the current, I doubt the current draw will be
anywhere near 2A. You'll probably want a decent heatsink though, and to get
closer to 13V you could bung 3 series diodes in the output of the regulator
output to give 15-2.1=12.9V. Take care to use diodes rated higher than the
current though, 1n400x might not be adequate. Again, they're only good for 1
Amp.

As for a replacement transistor, just about any power transistor of similar
(or better) rating and similar physical size will do, it isn't critical in
this application. You could use something in a TO220 package like a TIP42c
which is a popular transistor here in the UK.

http://www.fairchildsemi.com/ds/TI/TIP42C.pdf

Dave
 
D

David C. Partridge

Jan 1, 1970
0
If the base is being driven by a 13.6V zener and the collector has 26V, then
I'd expect a 13V output on the emitter.

---.--------.---------------------. -26V
| | |
| x |
| x 5k6 |
| x |
| | |/
= 100uF .-----.--xxxx--------|
| | | 470R |<\
| V | |----- -13V
| ~ ZD = 10uF = 10uF
| | | |
---.--------.-----.----------------.----- 0V

If the above is about right then any PNP with a suitable rating should do,
and no you probably can't use the VR you have as -15V will probably be too
high for the following circuits.

Dave
 
G

GregS

Jan 1, 1970
0
2SB527 PS TO125 110 v 90v 5v 2A 10WT 50minHFE
Froms Towers Transistor Selector No freq. given.

There is also some crosses at
http://www.ee.washington.edu/circuit_archive/parts/cross.html

Also my page.
http://www.pitt.edu/~szekeres/shopchip.htm

I forgot to list the USA/Euro equivalant, also in the Towers book.
2n5180 and Euro BD140


Type in BD140 in findchips.com

Most people would just use the NTEreplacement.
I found a distributor who claims to sell this Towers
International Transistor Selector from 1977 ??

greg
 
D

Dave

Jan 1, 1970
0
GregS said:
2SB527 PS TO125 110 v 90v 5v 2A 10WT 50minHFE
Froms Towers Transistor Selector No freq. given.

That's odd... I am finding all over the place on the net:

2SB527 TO220 110V 100V 0A8 10W 50minHFE 300maxHFE

That's 800mA rated, not 2A. Where did you get 2A rating?
 
G

GregS

Jan 1, 1970
0
That's odd... I am finding all over the place on the net:

2SB527 TO220 110V 100V 0A8 10W 50minHFE 300maxHFE

That's 800mA rated, not 2A. Where did you get 2A rating?

Towers International Transistor Selector book.
2A max, 500ma hfe test.


I read again with magnifiers, thats TO126 package. Perhaps the orginator
can identify which case?? TO220 or TO126 ??
 
D

Dave

Jan 1, 1970
0
GregS said:
Most people would just use the NTEreplacement.
I found a distributor who claims to sell this Towers
International Transistor Selector from 1977 ??

greg
The more I read the responses, the more confused I get. There appears to be
literally hundreds of thousands of different transistors. They have various
ratings including, but not limited to:

ECO
EBO
BCO
Ic
Ib
hFE (min AND max)
Pd in Watts

Which ones need I concern myself with? The various "cross-reference" pages
all give different results when presented with search keywords. The most
confusing term I see is hFE... I consulted a catalog (digikey) to try to get
a handle on how these ratings correspond to each other, the various
packages, etc. The "hFE" rating may jump from 25 to 1000 between a "40V,
1A" and a "60V, 2A" transistor. ???

What I mean is, without getting into the meat of transistor theory and
operation (yeah, I know, I've got to go there sometime), is there a simple
way for me to pick an "equal or greater value" transistor to replace my bad
one? For example another poster suggested TIP42C as a replacement.

Here's how they stack up

Parameter 2SB527 TIP42C
V(CBO) 100 100
V(CEO) 110 100
Ic 0.8A 6A
Pd 10 10

I was all happy until I saw the hFE rating. This is a measure of
transistor's gain. There was no absolute maximum gain given for the TIP42C,
the value is "30" at 0.3A, so I'd imagine that might approach the value of
"55" given as the absolute max on the 2SB527 as Ic approaches zero on the
TIP42C.

Thanks a lot for your assistance so far, I think I'll rummage around a bit
and see if I can scare up ANY PNP power transformer rated at >100V and >1A.
 
G

GregS

Jan 1, 1970
0
GregS said:
The more I read the responses, the more confused I get. There appears to be
literally hundreds of thousands of different transistors. They have various
ratings including, but not limited to:

ECO
EBO
BCO
Ic
Ib
hFE (min AND max)
Pd in Watts

Which ones need I concern myself with? The various "cross-reference" pages
all give different results when presented with search keywords. The most
confusing term I see is hFE... I consulted a catalog (digikey) to try to get
a handle on how these ratings correspond to each other, the various
packages, etc. The "hFE" rating may jump from 25 to 1000 between a "40V,
1A" and a "60V, 2A" transistor. ???

What I mean is, without getting into the meat of transistor theory and
operation (yeah, I know, I've got to go there sometime), is there a simple
way for me to pick an "equal or greater value" transistor to replace my bad
one? For example another poster suggested TIP42C as a replacement.

Here's how they stack up

Parameter 2SB527 TIP42C
V(CBO) 100 100
V(CEO) 110 100
Ic 0.8A 6A
Pd 10 10

I was all happy until I saw the hFE rating. This is a measure of
transistor's gain. There was no absolute maximum gain given for the TIP42C,
the value is "30" at 0.3A, so I'd imagine that might approach the value of
"55" given as the absolute max on the 2SB527 as Ic approaches zero on the
TIP42C.

Thanks a lot for your assistance so far, I think I'll rummage around a bit
and see if I can scare up ANY PNP power transformer rated at >100V and >1A.

I'm still showing BD140 as a replacement for a 2SC527 TO126

Raising max current usually lowers HFE, so keep it near.
As long as the voltages are above, don't worry too much unless
your driving max current which stresses max voltage limits.
Keep HFE rating near. Changing parameters too much may
cause circuit opperation changes.Generally, higher voltage transistors
have less current gain. Darlington's have a magnitude greater
HFE's

greg
 
D

Dave

Jan 1, 1970
0
GregS said:
GregS said:
1A.

I'm still showing BD140 as a replacement for a 2SC527 TO126

AHHHH, I am seeking replacement of 2S_B_527, not 2S_C_527 as you note,
above.
Raising max current usually lowers HFE, so keep it near.
As long as the voltages are above, don't worry too much unless
your driving max current which stresses max voltage limits.
Keep HFE rating near. Changing parameters too much may
cause circuit opperation changes.Generally, higher voltage transistors
have less current gain. Darlington's have a magnitude greater
HFE's

By "near", what do you mean. I looked at the hFE vs. DC amps for the TIP42C
and it appears to range from about 20 to 100, whereas the 2SB527 is spec'ed
at 55 to 300. Close enough? I can't find a curve for the 2SB527. The
NTE292 looks pretty good too with hfe of 15 to 150.
 
G

G

Jan 1, 1970
0
Howdy Dave......I like your simple solution to use a 7915 from your junk
box and in the process, simplifying your circuitry a little! Of course
my first choice would have been something like a 7912 with a single gen
purpose diode (1N4001 etc) inserted in the leg to ground to bump the reg
voltage output up nearer to 13. With your 7915 you could likewise add a
couple of similar diodes in series with the output to lower the voltage
to your load.

Keep on tinkering.


Gord
 
D

Dave

Jan 1, 1970
0
G said:
Howdy Dave......I like your simple solution to use a 7915 from your junk
box and in the process, simplifying your circuitry a little! Of course
my first choice would have been something like a 7912 with a single gen
purpose diode (1N4001 etc) inserted in the leg to ground to bump the reg
voltage output up nearer to 13. With your 7915 you could likewise add a
couple of similar diodes in series with the output to lower the voltage
to your load.

Keep on tinkering.

I'd like to go the diode route as they are more readily available than any
particular transistor. How would I wire them up as relates to my 7915 to
drop (actually raise) the voltage by 2V to -13VDC?

Each diode has a voltage drop and I just string 'em together to add up to
2VDC and tie them from the output of the 7915 to ground? I always figured a
diode was like a one-way resistor. Could I just use a resistor to ground to
get rid of some of my voltage? And, if so, how do I size it if I don't know
my current through the circuit? (I can't measure it, the transistor is
dead). Trial and error is a laborious process.

How can a diode RAISE the voltage of a 7912 (I'll dig around, might have one
somewhere)? Thanks a lot and pardon my ignorance.

Dave
 
G

G

Jan 1, 1970
0
Dave you wouldn't put the diodes from the 7915 output to ground but from
the output to your load in series......being a negative polarity output
you'd put the cathode towards the 7915 (and any additional diodes as well).

The trick to bumping up the voltage of a 3 terminal fixed regulator is
to insert a diode between the ground pin and ground (keep in mind to
insulate the tab if you do this!). The regulated voltage will now be
pushed up by the junction voltage of the diode or diodes (Diodes placed
as such in a 7912 would have their cathode face the ground pin.....anode
to ground).

clear as mud?
 
G

G

Jan 1, 1970
0
You mentioned not knowing the load current Dave.....(with the limits
that you could look up the max collector current and device dissipation
for the old device and deduce a ballpark figure). The beauty of using
the diodes is that they behave (when forward biased...within their
normal operating range) as a somewhat-constant voltage drop despite
current.....thus no big math for some quick trials.

Gord
 
C

Chuck

Jan 1, 1970
0
I've identified a bad transistor in the power supply of an audio component,
circa 1981. It's a 2SB527 PNP transistor... I had a bit of a look around on
the net and didn't find any quick easy sources. This transistor's sole
function is to convert -26VDC coming off one side of a bridge rectifier
to -13 volts. It's wired up as follows, and I apologize for not being more
skilled in ascii art or I'd try to draw it.

The collector is the -26VDC input. It is connected to ground via a 100uF
cap.
The emitter is the -13VDC output. It is connected to ground via a 10uF cap.
The base is connected to a series 470-ohm resistor, then a parallel 10uF cap
(to ground), then a parallel zener diode (to ground), then a 5.6K-ohm
resistor, then to the collector.

My question is thus: if my downstream components can get by with -15VDC,
can I just substitute a 7915 15VDC negative voltage regulator? There are no
feedback connections from any other part of my circuit to this transistor,
it's output voltage should not vary under normal conditions. And, by freak
coincidence, the pinout of the regulator matches my circuit perfectly, it'd
be a straight swap and removing a couple of resistors. And perhaps most
importantly, I have one.

We used to sub a 2sb633 which cost about a U.S. dollar. Chuck
 
G

GregS

Jan 1, 1970
0
It's a TO-220 looking at it...

If its a TO220 then its a TO220.
I found my Japanese cross reference book. Here goes. Still a TO126

2SB527 SAN 2SB631 TOS 2SA815 NEC 2SA985 MAT 2SA1110 ROHM 2SB1085

A trouble may reside in you transistor manufacturer. You would have to look
at the manufacturers spec sheet to get exact figures.

If you make a regulator with diodes, put some capacitance across
the diodes.

greg
 
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