low volt drop tranny

exxos · Jul 30, 2003

Hi all,

Does anyone know of any transistors which have little voltage drop across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though after
it switches on I only get around 10.5volt out max. I wonder if there are any
better versions out there which less volt-drop across them ??

TIA,
Chris

scada · Jul 30, 2003

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...

Hi all,

Does anyone know of any transistors which have little voltage drop across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

Jim Thompson · Jul 30, 2003

On Wed, 30 Jul 2003 21:31:46 GMT, "scada"
<scadaxxxxx@optonlinenospam.net> wrote:

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

TIP132 is an NPN Darlington so you're basically seeing a drop equal to
two Vbe's.

A PNP Darlington would improve to a Vbe plus a Vsat, but as "Exxos"
pointed out a MOSFET is your best bet.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice

480)460-2350 | |
| Jim-T@analog_innovations.com Fax

exxos · Jul 30, 2003

"scada" <scadaxxxxx@optonlinenospam.net> wrote in message
news:6PWVa.16350$W93.4728052@news4.srv.hcvlny.cv.net...

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop
across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though
after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

already tried, it seems you need a gate voltage of say 10volts to get a
conduction votlage of just 8 volts across it.

Jim Thompson · Jul 30, 2003

On Wed, 30 Jul 2003 22:54:55 +0100, "exxos" <exxos@home.co.uk> wrote:

"scada" <scadaxxxxx@optonlinenospam.net> wrote in message
news:6PWVa.16350$W93.4728052@news4.srv.hcvlny.cv.net...

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop
across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though
after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

already tried, it seems you need a gate voltage of say 10volts to get a
conduction votlage of just 8 volts across it.

Use a P-Channel device. Do you have a hang-up for N-type devices ?

480)460-2350 | |
| Jim-T@analog_innovations.com Fax

Boris Mohar · Jul 30, 2003

On Wed, 30 Jul 2003 22:54:55 +0100, "exxos" <exxos@home.co.uk> wrote:

"scada" <scadaxxxxx@optonlinenospam.net> wrote in message
news:6PWVa.16350$W93.4728052@news4.srv.hcvlny.cv.net...

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop
across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though
after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

already tried, it seems you need a gate voltage of say 10volts to get a
conduction votlage of just 8 volts across it.

Than you are doing it wrong. Gate voltage with respect to what?
What is "conduction voltage" ? You can get a mosfet with few milliohms
of on resistance. Just how much voltage drop will that cause?

--

Boris Mohar

CWatters · Jul 31, 2003

If the TIP132 is a darlington then the loss you are seeing is because the
emmitter voltage must be less than 2 x 0.7 =1.4V below the base or it turns
off.

If you change the TIP132 to a PNP device you should get that "drop out" down
(to about 1V if I remember correctly =Vbe+Vsat). If you use a PNP device the
you also need to invert the signal driving the base (perhaps using a small
NPN transistor).

A P-Channel FET would reduce it further. You need one with a gate threshold
(Vgt) of around 6V or less and an ON-Resistance of...

Ron=Von/5A eg a 0.5V drop requires Ron < 100mOhms and a 0.05V drop <
10mOhms

You could also use an N-Channel FET and a charge pump to produce a gate
voltage of more than 12V + Vgt but that's getting messy.
Colin

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...

Hi all,

Does anyone know of any transistors which have little voltage drop across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though after
it switches on I only get around 10.5volt out max. I wonder if there are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

exxos · Jul 31, 2003

"Boris Mohar" <borism@sympatico.ca> wrote in message
news

2hgivsclo3d68e86tglca91ivitaf1tjo@4ax.com...

On Wed, 30 Jul 2003 22:54:55 +0100, "exxos" <exxos@home.co.uk> wrote:

"scada" <scadaxxxxx@optonlinenospam.net> wrote in message
news:6PWVa.16350$W93.4728052@news4.srv.hcvlny.cv.net...

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop
across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though
after
it switches on I only get around 10.5volt out max. I wonder if there
are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

already tried, it seems you need a gate voltage of say 10volts to get a
conduction votlage of just 8 volts across it.

Than you are doing it wrong. Gate voltage with respect to what?
What is "conduction voltage" ? You can get a mosfet with few milliohms
of on resistance. Just how much voltage drop will that cause?

--

With a 12VDC input to gate and drain you only get 9VDC output from a W20NB50
( only use as it was the only fet I had to hand )

chris

Boris Mohar

exxos · Jul 31, 2003

"CWatters" <colin.watters@pandora.be> wrote in message
news:4j6Wa.42687$F92.4673@afrodite.telenet-ops.be...

If the TIP132 is a darlington then the loss you are seeing is because the
emmitter voltage must be less than 2 x 0.7 =1.4V below the base or it
turns
off.

If you change the TIP132 to a PNP device you should get that "drop out"
down
(to about 1V if I remember correctly =Vbe+Vsat). If you use a PNP device
the
you also need to invert the signal driving the base (perhaps using a small
NPN transistor).

A P-Channel FET would reduce it further. You need one with a gate
threshold
(Vgt) of around 6V or less and an ON-Resistance of...

Ron=Von/5A eg a 0.5V drop requires Ron < 100mOhms and a 0.05V drop
10mOhms

You could also use an N-Channel FET and a charge pump to produce a gate
voltage of more than 12V + Vgt but that's getting messy.
Colin

I didn't need a darlington so I used a TIP41 which has the volt drop down to
about 0.5volts, a lot beter. I've not had much luck with the fets so far. A
pump could work though as you say its getting messy. I wonder if theres any
reasonable germanium trannys still out there, 0.5 drop for a TIP41 is near
enough I guess,

cheers,
Chris

CWatters · Jul 31, 2003

This is the sort of circuit we are trying to get you to use (best I could
find without drawing one myself)...

http://www.rason.org/Projects/transwit/transwit.htm

See Fig 1

Note that a 2N3906 is not the right device for you as it won't take the
power.

Use a power transistor with a low Vcesat or better still a P type FET.

Colin

Watson A.Name - 'Watt Sun · Aug 1, 2003

In article <3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com>,
exxos@home.co.uk mentioned...

Hi all,

Does anyone know of any transistors which have little voltage drop across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though after
it switches on I only get around 10.5volt out max. I wonder if there are any
better versions out there which less volt-drop across them ??

It _has_ to have at least a volt or more drop because it's a
Darlington transistor! Two emitter to base junctions at .6 V each.
So get rid of the single transistor and use two separate transistors,
with the second transistor's base driven by the first transistor's
emitter. Don't forget to include a current limiting resistor in
series with the base. The first transistor's collector goes directly
to the positive supply, _not_ to the collector of the second.

TIA,
Chris

--
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exxos · Aug 1, 2003

"CWatters" <colin.watters@pandora.be> wrote in message
news:dmgWa.43592$F92.4634@afrodite.telenet-ops.be...

This is the sort of circuit we are trying to get you to use (best I could
find without drawing one myself)...

http://www.rason.org/Projects/transwit/transwit.htm

See Fig 1

I know this is what everyone is saying and see the diagram though I dont
think the PNP will give any better results than the NPN im using, both still
have volt drop. I guess we could argue over a few milivolts though I dont
see anything speical towards a PNP. I even tried one and can't say theres
much noticeiable difference, well apart from the circuit works backwards
with a PNP ;-)

Chris

Note that a 2N3906 is not the right device for you as it won't take the
power.

Use a power transistor with a low Vcesat or better still a P type FET.

Colin

Jim Thompson · Aug 1, 2003

On Fri, 1 Aug 2003 19:44:22 +0100, "exxos" <exxos@home.co.uk> wrote:

"CWatters" <colin.watters@pandora.be> wrote in message
news:dmgWa.43592$F92.4634@afrodite.telenet-ops.be...
This is the sort of circuit we are trying to get you to use (best I could
find without drawing one myself)...

http://www.rason.org/Projects/transwit/transwit.htm

See Fig 1

I know this is what everyone is saying and see the diagram though I dont
think the PNP will give any better results than the NPN im using, both still
have volt drop. I guess we could argue over a few milivolts though I dont
see anything speical towards a PNP. I even tried one and can't say theres
much noticeiable difference, well apart from the circuit works backwards
with a PNP ;-)

Chris

480)460-2350 | |
| Jim-T@analog_innovations.com Fax

Boris Mohar · Aug 2, 2003

On Thu, 31 Jul 2003 16:54:26 +0100, "exxos" <exxos@home.co.uk> wrote:

"Boris Mohar" <borism@sympatico.ca> wrote in message
news2hgivsclo3d68e86tglca91ivitaf1tjo@4ax.com...
On Wed, 30 Jul 2003 22:54:55 +0100, "exxos" <exxos@home.co.uk> wrote:

"scada" <scadaxxxxx@optonlinenospam.net> wrote in message
news:6PWVa.16350$W93.4728052@news4.srv.hcvlny.cv.net...

"exxos" <exxos@home.co.uk> wrote in message
news:3f281e77$0$15038$cc9e4d1f@news.dial.pipex.com...
Hi all,

Does anyone know of any transistors which have little voltage drop
across
them ? I am currently using a TIP132 ( 5A job ) on a 12V feed though
after
it switches on I only get around 10.5volt out max. I wonder if there
are
any
better versions out there which less volt-drop across them ??

TIA,
Chris

Use a MOSFET

already tried, it seems you need a gate voltage of say 10volts to get a
conduction votlage of just 8 volts across it.

Than you are doing it wrong. Gate voltage with respect to what?
What is "conduction voltage" ? You can get a mosfet with few milliohms
of on resistance. Just how much voltage drop will that cause?

--

With a 12VDC input to gate and drain you only get 9VDC output from a W20NB50
( only use as it was the only fet I had to hand )

chris

Did you conclude from that experiment that it is not worth pursuing
using a more suitable device as others have suggested?

Take a right hand glove and try it on your left hand. Eventually you will
manage to cram it on but it will not feel comfortable. Now turn it inside
out. Fits little better but still not quite right. All the fuzz is on
the outside.

Use a P channel mosfet.

--

Regards,

Boris Mohar
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Aurora, Ontario

John Fields · Aug 3, 2003

On Fri, 1 Aug 2003 19:44:22 +0100, "exxos" <exxos@home.co.uk> wrote:

I know this is what everyone is saying and see the diagram though I dont
think the PNP will give any better results than the NPN im using, both still
have volt drop. I guess we could argue over a few milivolts though I dont
see anything speical towards a PNP. I even tried one and can't say theres
much noticeiable difference, well apart from the circuit works backwards
with a PNP ;-)

---
Since you've implied that you're using a high-side driver,

+12
|
|
C
+12--[R]---B NPN
E
|
[RL]
|
GND

what that means is that as the voltage across the load increases, the
emitter voltage will also increase and the base voltage will have to
rise to one Vbe drop above the emitter in order to keep the transistor
turned on. If you have a 12V supply connected to the collector and you
drive the base to 12V, then the load _has_ to be at least one Vbe below
12V in order to allow the transistor to be turned on. If you use a PNP,
then you're essentially creating a low-side driver because the load will
appear between the collector and what the PNP considers to be its
supply, ground.

+12
|
|
E
GND--[R]---B PNP
C
|
[RL]
|
GND

Now, with the PNP driven into saturation by driving its base more
negative than its emitter, only Vce(sat) will keep the voltage across
the load from rising to the supply voltage.

OTOH, If you're using a low side driver:

+12
|
[RL}
|
C
+12--[R]---B NPN
E
|
|
GND

then you've got other problems.

--
John Fields

Andre · Aug 5, 2003

"CWatters" <colin.watters@pandora.be> wrote in message news:<bAAWa.44876$F92.4763@afrodite.telenet-ops.be>...

"Jim Thompson" <Jim-T@analog_innovations.com> wrote in message
news:4hdliv8bnjibnndjlga50oekqd8odj7hjh@4ax.com...

Sigh!

Well he does have a point to some extent. With the NPN he's limited by Vbe
(0.7V) and with a PNP it's Vcesat (0.3V) perhaps worse...but I agree with
the sigh...

FETs are the best option. In my garage I've got a matchbox size device that
switches 100A+ using loads of small SMD FETs in parallel to minimise the on
resistance and voltage losses. Not my design though.

Cool !

Any chance of a schematic (or is it just a lot of 1 Amp FETs
in parallel ?)

Colin

CWatters · Aug 6, 2003

"Andre" <testing_h@yahoo.com> wrote in message
news:2c2cf14c.0308051120.7a2f1bdf@posting.google.com...

Cool ! Any chance of a schematic (or is it just a lot of 1 Amp FETs
in parallel ?)

Not my design. You can buy them from...

http://www.kontronik.com/

They are used to power competition electric model aircraft.

See the "Beat FAI 24" as an example of the top of the range.

low volt drop tranny

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