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Using Arduino => General Electronics => Topic started by: diode on Apr 01, 2013, 04:24 pm

Title: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: diode on Apr 01, 2013, 04:24 pm
Hi,
Can anyone here think of a good logic level P channel MOSFET that can deal with about 40v, 1A? 
Have been searching the internet for hours and thought to try here..
Thanks!
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: fungus on Apr 01, 2013, 04:29 pm

Can anyone here think of a good logic level P channel MOSFET that can deal with about 40v, 1A?  


I think most of them can handle that much power. Probably quite a few BJTs, too.

Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: johnwasser on Apr 01, 2013, 04:35 pm
You can do parametric searches at both DigiKey.com and Mopuser.com.

At DigiKey I put in the search term 'logic level mosfet'.

Then clicked on "FETs - Single".

Then under FET Type selected "MOSFET P-Channel"

Under Vdss I selected for 40V,45V,or 50V

You can figure out the rest.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: AlxDroidDev on Apr 01, 2013, 04:37 pm
I'd say nearly all of them. It'd be more trouble to find one than CAN'T handle that than one that can.

1A at 40V is nothing for a MOSFET, provided they have a cooling rib.

Here's a brief list from Vishay: http://www.vishay.com/mosfets/p-channel/v-ds-gteq-neg31-v-lteq-neg80-v/
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: Riva on Apr 01, 2013, 04:38 pm
How about this (http://arduino.cc/documents/datasheets/MOS-irf520npbf.pdf).
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: AlxDroidDev on Apr 01, 2013, 04:43 pm

How about this (http://arduino.cc/documents/datasheets/MOS-irf520npbf.pdf).


Isn't the IRF520 a N-channel MOSFET ? I believe the OP needs a P-channel.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: diode on Apr 01, 2013, 04:51 pm
Thanks all! Will look at those resources - there are so many.

Was just wondering if there is one or some that are particularly good / easy to interface / power efficient etc.

(like for example the IRF540 N Channel seems to come recommended as an N Channel)

Reading into it also seems they have become much better over time.

ps. yes the IRF520 is N.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: CrossRoads on Apr 01, 2013, 04:57 pm
You are using this as a high side switch device?
To drive from an Arduino pin, you will need NPN or logic level N-channel to pull the P-channel's gate low to turn it on, with pullup resistor to 40V to turn it off.
I posted a circuit yesterdy to do that, for driving a halogen lamp.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: CrossRoads on Apr 01, 2013, 05:00 pm
Replace the PNP with P-channel MOSFET
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: diode on Apr 01, 2013, 05:02 pm
CrossRoads - I want to connect them to a TLC5940. Am presuming a P channel MOSFET can connect straight to a TLC.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: CrossRoads on Apr 01, 2013, 05:10 pm
TLC5940 datasheet says it needs some minimal load to switch properly.
Use a low enough value resistor as the Pullup resistor to 40V to meet that.
The TLC5940 will act as the NPN transistor here.
Have not tried this myself, wire up just 1 MOSFET to start and see  how it works.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: diode on Apr 01, 2013, 05:13 pm
Thanks for your thoughts!
Not sure what you mean with the minimal load?
Haven't got a P channel MOSFET at hand so have to get one and try tomorrow.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: sparkylabs on Apr 01, 2013, 09:36 pm
What exactly are you trying to do with the mosfet ? if your switching loads then low side switching is best if possible because N channel devices are cheaper and have better characteristics.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: JoeN on Apr 01, 2013, 11:03 pm

What exactly are you trying to do with the mosfet ? if your switching loads then low side switching is best if possible because N channel devices are cheaper and have better characteristics.


But a TLC5940 is already a low-side PWM controller that sinks current.  So for a matrix, as an example, if the columns are cathodes you use the TLC9540 to control the columns.  This leaves you to control the rows (anodes), on the high side.  How do you use N-channel for that?  The general way to solve that from what I have seen is P-channel MOSFETs or maybe darlingtons on the high side to source current.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: sparkylabs on Apr 01, 2013, 11:15 pm
yes in that case it has to be high side. unless the LED's are powered from 5v he needs level shifting too as suggested above
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: CrossRoads on Apr 02, 2013, 01:13 am
Minimal Load:

See Page 14 of data sheet:

The maximum output current per channel is programmed by a single resistor, R(IREF), which is placed between
IREF pin and GND pin. The voltage on IREF is set by an internal band gap V(IREF) with a typical value of
1.24V. The maximum channel current is equivalent to the current flowing through R(IREF) multiplied by a factor of
31.5. The maximum output current per channel can be calculated by Equation 6:
Imax = V(iref)/R(iref) x 3.15

where:
V(IREF) = 1.24 V
R(IREF) = User-selected external resistor.
Imax must be set between 5 mA and 120 mA. The output current may be unstable if Imax is set lower than 5 mA.
Output currents lower than 5 mA can be achieved by setting Imax to 5 mA or higher and then using dot
correction.
Title: Re: Anyone know a strong P channel MOSFET (about 40v, 1A, logic level) ?
Post by: MarkT on Apr 02, 2013, 01:39 am
If you are choosing a MOSFET by drain-current parameter you are probably going about things
the wrong way.

No-one would normally take a MOSFET near its max rated current value - it will need LARGE heatsink
and will dump tonnes of power.

Use the Rds(on) figure to decide if a device is suitable - you can calculate the power dissipation and
voltage drop directly from that - make sure both are sensible.  Also remember power goes as the
square of current so that 10A is four times worse than 5A for the same device - this really can bite
the unwary.  Do the maths to avoid surprises.