Logic Level MOSFET

Hi,
I'm looking for a N-ch and a P-ch MOSFET that can handle 24V 6A and will switch on with the current from a PC's parallel port and it's voltage 3,3V.

Anyone?

Thanks in advance!

PS, I need it to a H-bridge that will run a 100W 24V DC motor.

Logic level Fets, like the IRL series from International Rectifier still require 4.5V on their gate. 3.3V is too low, and a much lower impedance source. You can easily fix this by adding some NPN small-signal transistors between the port and the gate. Write back if you need a diagram.

Thanks MiikeMI! Please do send me the diagram!! I have a lots of small signal transistors so that shouldn't be a problem, just let me know how to wire it up! =)

olof102 said:

Thanks MiikeMI! Please do send me the diagram!! I have a lots of small signal transistors so that shouldn't be a problem, just let me know how to wire it up! =)

Click to expand...

One other caution: When a PC boots up, the parallel port pins do a complicated dance (I'm guessing that is used by the mother board manufacturer for testing). If your 24V power supply is turned on during PC boot-up, the port pins may hit the exact pattern that happens to turn on both the top and bottom transistor of your H-bridge, which will blow up something.

Last time I did this, I had to use a decode of the port pins and some of the bits from one of the status registers to enable the external drivers. I experimentally had to find a unique bit pattern which never happens during the boot-up sequence.

One other question: Will you be controlling the gates of the high-side (P-Channel FETs) from the PP? (IOW: are you using 2bits from the PP or 4?)

Oh, then I'll keep in mind to dissconnect the cable between computer and H-bridge during startup.

Sorry for noob questions, How do I know if I'm using 2 bits or 4 bits?
I have written a proram in C++.

Code:
#include <stdio.h>
#include <dos.h>

void main(void)
{outportb(0x378,0x00);
};

00 = 0V on datapins
01 = 3,3V on Datapin1
02 = 3,3V on Datapin 2
And so on I guess...?

Is this what you mean?

Will I be able to control the direction of the motor with this code?

Thanks!

olof102 said:

Oh, then I'll keep in mind to dissconnect the cable between computer and H-bridge during startup.

Sorry for noob questions, How do I know if I'm using 2 bits or 4 bits?
I have written a proram in C++.

Code:
#include <stdio.h>
#include <dos.h>

void main(void)
{outportb(0x378,0x00);
};

00 = 0V on datapins
01 = 3,3V on Datapin1
02 = 3,3V on Datapin 2
And so on I guess...?

Is this what you mean?

Will I be able to control the direction of the motor with this code?

Thanks!

Click to expand...

Read this thread. This is an example of an H-Bridge that can be controlled with only two bits.