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Dual transistors

E

Ed

Jan 1, 1970
0
The circuit described at
http://www.far-out.demon.co.uk/cardiy/tempgage.htm is to improve the
dash temperature gauge performance on certain Jaguars. I'd like to
try the circuit, but it calls for
a dual transistor and suggests 2N4014 and that is not a dual. What
about something like NTE 45
http://www.nteinc.com/specs/10to99/pdf/nte44_45.pdf?
Also, I get a bit worried when a project like this doesn't give
correct part numbers.

Is this circuit likely to perform as described in the article?

TIA

Ed
 
M

Meat Plow

Jan 1, 1970
0
The circuit described at
http://www.far-out.demon.co.uk/cardiy/tempgage.htm is to improve the
dash temperature gauge performance on certain Jaguars. I'd like to
try the circuit, but it calls for
a dual transistor and suggests 2N4014 and that is not a dual. What
about something like NTE 45
http://www.nteinc.com/specs/10to99/pdf/nte44_45.pdf?
Also, I get a bit worried when a project like this doesn't give
correct part numbers.

Is this circuit likely to perform as described in the article?

TIA

Ed

Use two singles and tie their bases together.
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COOSN-266-06-25794
 
E

Ed

Jan 1, 1970
0
According to the designer, two singles won't work well because it
would be
difficult to keep the base temperatures precisely the same. But he
does suggest
that as an alternative, using power transistors clamped together with
thermal paste.

BTW, I have sent e-mail to him, but no reply. He may have lost
interest, or
doesn't check e-mail very often.

Thanks.

Ed
 
P

Phil Allison

Jan 1, 1970
0
"Ed"
The circuit described at
http://www.far-out.demon.co.uk/cardiy/tempgage.htm is to improve the
dash temperature gauge performance on certain Jaguars. I'd like to try
the circuit, but it calls for
a dual transistor and suggests 2N4014 and that is not a dual.


** The 2N4044 is a dual - however an NPN one !



** No, the emitters are commoned - so no good for you.




........ Phil
 
G

Gareth

Jan 1, 1970
0
Ed said:
According to the designer, two singles won't work well because it
would be difficult to keep the base temperatures precisely the same.
But he does suggest that as an alternative, using power transistors
clamped together with thermal paste.

BTW, I have sent e-mail to him, but no reply. He may have lost
interest, or doesn't check e-mail very often.

Thanks.

Ed

What country are you in? it may help us to recommend suppliers.

Do you know how much current the transistor needs to handle?

There are quite a few dual PNP transistors in very small surface mount
packages, but I expect they would be quite fiddly to solder?

see and select "PNP (Dual)" under "transistor polarity" on the page below:

http://uk.farnell.com/jsp/search/browse.jsp?N=411+1000052

The only dual PNP I can think of right now in a leaded package is the
MAT-03. This is a precision audio part (that means expensive). I don't
know if it is suitable though.

http://www.analog.com/en/prod/0,,773_865_MAT03,00.html

Given the errors you have discovered so far with this design, I'm not
sure I would want to fit it to my car.


--
 
E

Eeyore

Jan 1, 1970
0
Ed said:
The circuit described at
http://www.far-out.demon.co.uk/cardiy/tempgage.htm is to improve the
dash temperature gauge performance on certain Jaguars. I'd like to
try the circuit, but it calls for
a dual transistor and suggests 2N4014 and that is not a dual. What
about something like NTE 45
http://www.nteinc.com/specs/10to99/pdf/nte44_45.pdf?

The emitters are commoned. Useless.

You know what I'd do ?

I'd get maybe 6 - 10 low cost, general purpose, low-to-medium power pnp
transistors but with decent current gain, such as the type you'd get as the
driver in a modest audio amp.

I'd find the 2 devices with the best match for Vbe and then glue them together
back-to-back (ensuring that the collector tabs are insulated) . That'll ensure
good thermal tracking.

Job done.

Graham
 
E

Eeyore

Jan 1, 1970
0
Ed said:
According to the designer, two singles won't work well because it
would be difficult to keep the base temperatures precisely the same.

It's the *die* temperatire that matters.

But he does suggest that as an alternative, using power transistors clamped
together with thermal paste.

Thermal paste is messy and not required here. Since there's no power involved
ordinary epoxy glue would do the job just fine.

Duals are rare as hen's teeth btw and *expensive*.

Use the 2 power transistor method.

Graham
 
E

Ed

Jan 1, 1970
0
What country are you in? it may help us to recommend suppliers.

I'm in California
Do you know how much current the transistor needs to handle?

Very low. I've measured the current through the sensor to be less than
100 mA.




Thanks, Gareth.


Ed
 
J

John Popelish

Jan 1, 1970
0
Ed said:
I'm in California


Very low. I've measured the current through the sensor to be less than
100 mA.

I guess the definition of "very low" depends on who is
asking. 100 mA from a 12 volt source can produce enough
heat to put a blister on your finger (1.2 watts). But that
is pretty low, compared to the current a cranking motor draws.

I think you can make the matching a lot less important if
you add a couple ohms in series with each emitter. I think
that mounting two TO-220 power tab transistors on the same
small heat sink (with insulated mounting) would make this
work just fine. Any PNP jellybean power tab should work,
like TIP30 or TIP32.
 
E

Eeyore

Jan 1, 1970
0
John said:
I think you can make the matching a lot less important if
you add a couple ohms in series with each emitter. I think
that mounting two TO-220 power tab transistors on the same
small heat sink (with insulated mounting) would make this
work just fine. Any PNP jellybean power tab should work,
like TIP30 or TIP32.

Beware the low beta for those devices. I forget how beta dependent the circuit
was or wasn't.

Graham
 
J

John Popelish

Jan 1, 1970
0
Eeyore said:
Beware the low beta for those devices. I forget how beta dependent the circuit
was or wasn't.

I think the circuit is a crude current mirror that boosts
the current that passes through the sensor by an adjustable
factor. Nothing precise about it. It is just a simple way
to expand the central part of the meter scale.
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore Idiot "
Beware the low beta for those devices. I forget how beta dependent the
circuit
was or wasn't.


** Bollocks.

A typical TIP31 /32 has a beta of * 150 *

with Vce = 2 volts & Ic =100mA.




......... Phil
 
E

Ed

Jan 1, 1970
0
John Popelish said:
I guess the definition of "very low" depends on who is asking. 100
mA from a 12 volt source can produce enough heat to put a blister on
your finger (1.2 watts).

Yes, you're right. Now I notice that the gauge has a 2W 50 ohm
resistor at the
sender input. Also, my calcs show the sender current can be up to
about 0.2A.
I think you can make the matching a lot less important if you add a
couple ohms in series with each emitter.

OK, once I settle on the transistors I'll do that.

I think that mounting two TO-220 power tab transistors on the same
small heat sink (with insulated mounting) would make this work just
fine. Any PNP jellybean power tab should work, like TIP30 or TIP32.

When I search for TIP30 at www.nteinc.com (easily available locally) I
am led
to NTE153, a PNP power transistor in the TO-220 package. However, I
notice
that h_fe1 can range from 40 to 200. It might be hard to get a pair
with "matched"
h_fe, if that is what is called for, ideally. I also notice that the
NPN version, NTE152,
is available as a matched pair, NTE152MP. A quick Google tells
me there are current mirror circuits based on NPN transistors. So, I'm
wondering
if I could use NPN in my application. Is that possible?


Ed
 
... Any PNP jellybean power tab should work, like TIP30 or TIP32.

When I search for TIP30 atwww.nteinc.com(easily available locally) I
am led
to NTE153, a PNP power transistor in the TO-220 package. However, I
notice
that h_fe1 can range from 40 to 200. It might be hard to get a pair
with "matched"
h_fe, if that is what is called for, ideally.
(snip)

Actually, what needs to be matched is the relationship between base to
emitter voltage and collector current. But adding 2 ohms in series
with each emitter adds an additional resistove drop to each effective
base to emitter (plus) resistor drop, that swamps out any mismatch in
this current range, so unmatched transistors can be used. These
resistors do not reduce the current gain of the transistors, but
increase the voltage required to turn them on (by 0.2 ams * 2 ohms =
0.4 volts, which totally reduces any millivolt difference in the ~.6
volt base emitter drop to insignificance, even if the two transistors
are not at the same temperature. You might be able to use 1 ohm
resistors (0.2 volts drop, max) and do almost as well, since this is
really not a high precision application.

John Popelish
 
M

Marra

Jan 1, 1970
0
The circuit described athttp://www.far-out.demon.co.uk/cardiy/tempgage.htmis to improve the
dash temperature gauge performance on certain Jaguars. I'd like to
try the circuit, but it calls for
a dual transistor and suggests 2N4014 and that is not a dual. What
about something like NTE 45http://www.nteinc.com/specs/10to99/pdf/nte44_45.pdf?
Also, I get a bit worried when a project like this doesn't give
correct part numbers.

Is this circuit likely to perform as described in the article?

TIA

Ed

So we have amateurs fixing Jag electronics ?
Well I wont be buying a Jag !
 
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