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Need Help in mosfet switching strobed LEDs

MiZZi

Sep 14, 2014
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That first diagram of your's just above doesn't make sense - the internal diode would be conducting and the MOSFET would not switch off.

I'm afraid you've lost me.

And in the second of your above diagrams, you're right back where you started - the top MOSFET couldn't be switched on until the gate was taken above the supply voltage.

Well, in the first diagram, I switched the P-Channel Mosfet (the one that I bought) into such in the diagram and it worked. The problem is it only works as a switching Mosfet if I use it like an N-Channel Mosfet.

Well, on the second diagram, I wanted to know if there was any other way that I could switch two N-Channels such as what I have posted here in the second diagram. Maybe, you have any idea I could accomplish that. Thanks by the way!
 

MiZZi

Sep 14, 2014
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So now you need to go and buy some 'real' P-channel MOSFETs. ;)

The problem sir its hard to find it here. I could buy it, but I'll have to wait for a week or two which is definitely not an option considering that I have to finish this as early as possible.
 

Old Steve

Jul 23, 2015
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Sounds like the P-channel has some strange internal arrangement with the internal diode backwards.

=MiZZi]Well, on the second diagram, I wanted to know if there was any other way that I could switch two N-Channels such as what I have posted here in the second diagram. Maybe, you have any idea I could accomplish that. Thanks by the way!

I actually explained this in post#3, near the beginning of this thread:-
I said:
The N-channel won't work on the upper side because the gate needs to be taken higher than the supply voltage to activate it. 4-5V higher for a logic-level MOSFET, otherwise about 10V for a normal one.
A 'high-side driver' could be used, but that's added expense and complexity.
A high-side driver is the answer.
A high-side driver generates a voltage higher than the supply voltage, usually using a switched-capacitor system. You could make one yourself, using a 555 timer, caps and diodes, but as I said, any high-side driver adds expense and complexity, for no good reason.

If you really want to do it that way, Google 'high-side driver' for more info.
It's much better to use a decent P-channel MOSFET though.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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That first diagram of your's just above doesn't make sense - the internal diode would be conducting and the MOSFET would not switch off.

I'm afraid you've lost me.

And in the second of your above diagrams, you're right back where you started - the top MOSFET couldn't be switched on until the gate was taken above the supply voltage.
You're not the only one lost here. I don't believe for a nanosecond that the FPQ27P06 is actually wired like that.

I've taken note that some, maybe all of the datasheets present the PCH schematic symbol inverted. IE Source on the top Drain on the bottom. The SparkFun link to the FPQ27P06 that was posted is an example of this. My guess is that it's displayed this way because PCHFETs are typically used this way when there's no negative power rail available.

Anyway my gut tells me that the FET is not connected as MiZZi thinks it is. I certainly don't believe that a PCHFET was mis - manufactured and is actually an NCH or that the internal diode was manufactured with the Cathode Anode reversed.

Chris
 

Old Steve

Jul 23, 2015
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Anyway my gut tells me that the FET is not connected as MiZZi thinks it is. I certainly don't believe that a PCHFET was mis - manufactured and is actually an NCH or that the internal diode was manufactured with the Cathode Anode reversed.
Chris
No, me neither. I just decided to go with the flow. :D
(The die would need to be re-built to do that.)
 

MiZZi

Sep 14, 2014
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Problem is now solved guys. Fortunately, I was able to find a P-Channel after days of canvassing. Thanks for all your help guys!
 
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