Help with MOSFET pinout for PIC programmer circuit

[Sim Joo Khai]

I have found (and am intending to build) Myke Predko's El Cheapo PIC
Programmer at www.rentron.com/Myke4.htm . However, there is a problem with
the Version 3.1 circuit diagram -- the MOSFET pinouts are not shown.

It is very clear that the gate of Q1 is connected to Pin 16 of the parallel
port, and the gate of Q2 is connected directly to Q1. The confusion comes in
when figuring out which is the drain and which is the source.

The 2N7000 is an N-channel Enhancement Mode MOSFET, while the ZVP2106A is a
P-channel Enhancement Mode MOSFET.

May I know ... ...

1) Is the pin of Q1 connected to GND the source or drain?
2) Is the pin of Q1 connected to R5 the source or drain?
3) Is the pin of Q2 connected to the positive supply rail the source or
drain?
4) Is the pin of Q2 connected to Pin 4 of the chip to be programmed the
source or drain?

Thanks in advance.

(N.B. I did not attach the circuit diagram in *.jpg format to this e-mail
for fear that it may be manipulated by viruses. Please go directly to the
site listed above for the schematic.)

Sim Joo Khai
Singapore

 

[Spehro Pefhany]

I have found (and am intending to build) Myke Predko's El Cheapo PIC
Programmer at www.rentron.com/Myke4.htm . However, there is a problem with
the Version 3.1 circuit diagram -- the MOSFET pinouts are not shown.

It is very clear that the gate of Q1 is connected to Pin 16 of the parallel
port, and the gate of Q2 is connected directly to Q1. The confusion comes in
when figuring out which is the drain and which is the source.

The 2N7000 is an N-channel Enhancement Mode MOSFET, while the ZVP2106A is a
P-channel Enhancement Mode MOSFET.

May I know ... ...

1) Is the pin of Q1 connected to GND the source or drain?
2) Is the pin of Q1 connected to R5 the source or drain?
3) Is the pin of Q2 connected to the positive supply rail the source or
drain?
4) Is the pin of Q2 connected to Pin 4 of the chip to be programmed the
source or drain?

http://www.fairchildsemi.com/ds/2N/2N7000.pdf
http://www.zetex.com/3.0/pdf/ZVP2106A.pdf


Best regards,
Spehro Pefhany

 

[Robert Monsen]

With N channel MOSFET devices, the major carrier of charge is electrons, so
the 'source' is usually kept more negative than the 'drain' (the electrons
are coming in through the source, and leaving through the drain...)

With P channel MOSFET devices, its the opposite, the major charge carriers
are holes, so the source of these holes is the positive side, while the
drain is the negative side.

N has negative source, P has positive source...

So, in your circuit, the side of the 2N7000 that is connected to ground is
the source, and the other side is the drain.

The side of the 2106 that is connected to the output of the regulator will
be the source (since that side is more positive, and this is a P channel
device...)

Good Luck with the project.

BTW, if you want to buy a PIC programming system for cheap, look at the
microchip website. I just got a PICKit starter kit, which uses USB, and
which will program the small 8 and 14 pin flash chips. It was about $40
bucks, I believe, and I didn't have to debug it.

DISCLAIMER: I'm not an EE, I'm a hobbyist, so take what I say with a grain
of salt.

Regards,
Bob Monsen