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4hv.org :: Forums :: General Science and Electronics
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A "totem pole switch" I got problem with basic electronics understanding.

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cavemen
Fri Jul 09 2010, 02:57AM Print
cavemen Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
 		We have anomaliously high temperature outside and our air conditioner broke.
It is too hot for me to think.

A tiny IC can drive POWERFUL devices at high frequencies with a Totem Pole switch.
That is when two transistors drive one powerful mosfet, one turns it on, other turns it off.
One transistor is PNP one is NPN and they have to be a complimentary pair. I found several darlington transistors to give me an ability to drive my moasfet with 3.3V push-pull or 5V. (Everything is on paper.)

I am developing a universal circuit to meet all my needs. (I will publish it when it works.)

I got a problem:
I want to bring that MOSFET voltage drop almost to 0 when it is on and get about 9V at the gate of the MOSFET. For some reason I can never get that high.

For some dumb reason it doesn't happen and I don't understand what variable I got to change. Darlingtons have a HFE of 12000 each.

Would this circuit work with a pair of complementary FIELD EFFECT TRANSISTORS?

I would like to know the math because I do math in excel as I design the circuit.
Thank you.
V.T.

circuit: Link2
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cavemen
Fri Jul 09 2010, 03:09AM
cavemen Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
 		The multisim 11 circuit of the device.
]totem_pole_dalington_switch.zip[/file]
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Avi
Fri Jul 09 2010, 07:52AM
Avi Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
cavemen wrote ...

The multisim 11 circuit of the device.

It should not be assumed that everyone has windows and multisim.
A screenshot would suffice.
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IntraWinding
Fri Jul 09 2010, 07:54AM
IntraWinding Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
 		Can you post a picture of your circuit?
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Patrick
Fri Jul 09 2010, 09:43PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Avi wrote ...


It should not be assumed that everyone has windows and multisim.
A screenshot would suffice.

even though i have win and multisim caveman, Avi makes a good point.
i demand a screen cap.
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Bjørn
Fri Jul 09 2010, 11:26PM
Bjørn Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
 		There is one linked in the very first post.
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IntraWinding
Sat Jul 10 2010, 01:25AM
IntraWinding Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Bjørn wrote ...

There is one linked in the very first post.

Ah, right, I didn't notice that the first time.

Picture of circuit here: Link2

cavemen: It looks like you've got the emitter and collector pins of Q1 reversed.
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cavemen
Sat Jul 10 2010, 03:19AM
cavemen Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
 		It makes no difference with the Q1 being upsidedown or right side up.
The voltage still doesn't exceed 9.7.

It looks like it has something to do with 12v and 3.3v causing some reverse - bias at the transistors.
I can calculate the discharge time (RC) of the MOSFET gate and loads, but I cannot understand what happens between the signal source and the darlingtons.

The gate voltage hangs aroung 6.8V
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cavemen
Sat Jul 10 2010, 03:38AM
cavemen Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
 		Does the circuit makes the output difference?
Doesn't look like it.
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cavemen
Sat Jul 10 2010, 04:55AM
cavemen Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
 		When I short the gate to +12V the MOSFET will open only to 9.8V.
12V exceed the maximum gate voltage rating of the mosfet, thing still ain't opening.
Something wrong with my understanding of the process.
1278737712 2008 FT92322 2version
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