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Topic: High Current High Side Switching (Read 809 times) previous topic - next topic

dl324

What would an ideal Q2 be? Something like an FQP7P06 ?
It'll do the job.  You could look for one with a lower on resistance and Id.  It would be uncommon for the source or drain to not be connected to the tab.
Quote
Since I'll be moving 2.5 amps (30 watts) through it, I assume a heatsink of some sort would be a good idea? If the tab is in fact electrically isolated, I could just run an aluminum bar across the tabs.
You're using the MOSFET as a switch.  A typical FQP7P06 would have an Rds(on) of about 350m ohms at 2.5A.  Power dissipation at 2.5A would be (2.5A)(2.5A)(350m ohms) = 2.2W.  A heatsink is still needed.

magnethead494

#16
Jun 29, 2019, 09:37 pm Last Edit: Jun 29, 2019, 09:45 pm by magnethead494
It'll do the job.  You could look for one with a lower on resistance and Id.  It would be uncommon for the source or drain to not be connected to the tab.You're using the MOSFET as a switch.  A typical FQP7P06 would have an Rds(on) of about 350m ohms at 2.5A.  Power dissipation at 2.5A would be (2.5A)(2.5A)(350m ohms) = 2.2W.  A heatsink is still needed.

Thanks. So i'll need to heatsink them individually somehow without allowing them to touch eachother, I take it. (I still find it odd the datasheet doesn't specify). Or use nylon nut and bolt and thermal pads.

dl324

You can buy insulators.

https://www.jameco.com/z/06-202-TEN--Heat-Sink-Mount-Kit-For-TO-220-Components-10-packs-_34121.html

Paul__B

I still find it odd the datasheet doesn't specify
You are right!  The datasheet is missing that critical detail.  The tab is almost always the same as the middle pin on any TO-220 package; they are presumably punched in one piece.

Mind you, that datasheet is actually from 2001 (down near the bottom).  That really is a rather poor device for your application, you would be much better off using a modern part requiring no heatsink.  If it is a SMD part, just use these adapters:

The chip plus the adapter will be no bigger than the TO-220 itself.  You will have a vastly more compact assembly.  :smiley-cool:

magnethead494

#19
Jun 30, 2019, 02:32 am Last Edit: Jun 30, 2019, 03:53 am by magnethead494
You are right!  The datasheet is missing that critical detail.  The tab is almost always the same as the middle pin on any TO-220 package; they are presumably punched in one piece.

Mind you, that datasheet is actually from 2001 (down near the bottom).  That really is a rather poor device for your application, you would be much better off using a modern part requiring no heatsink.  If it is a SMD part, just use these adapters:

The chip plus the adapter will be no bigger than the TO-220 itself.  You will have a vastly more compact assembly.  :smiley-cool:

What would be a better P-channel Mosfet? I've only done a few pieces in SMD and none of them were exactly pretty; granted 3 pins on an 0.1 spacing is easier than 10 pins on a .0254 spacing.

Paul__B

Searching "P-channel logic level FET" ...

Well, this one would be an excellent choice but is in a "DPAK" format - small but somewhat easier than a SOT-23.

This old one would appear to be adequate, not logic level but since you are going to drive it with at least 10 V, it should switch your 2.5 Amps easily with no heatsink.

And it is in a TO-220 package.

(By all means, someone can check my reading of the datasheets.  :smiley-lol: )


magnethead494

Searching "P-channel logic level FET" ...

Well, this one would be an excellent choice but is in a "DPAK" format - small but somewhat easier than a SOT-23.

This old one would appear to be adequate, not logic level but since you are going to drive it with at least 10 V, it should switch your 2.5 Amps easily with no heatsink.

And it is in a TO-220 package.

(By all means, someone can check my reading of the datasheets.  :smiley-lol: )


I work 1 block from Mouser Headquarters, so I've been going through their website. I just don't know how to tell crap from, well, not crap...on top of limiting options by minimum voltage and current load.

magnethead494

So i'm about to start building this project.

Question: So using a ULN2803A as the low side driver to drive the FQP27P06 P-Channel QFET high side driver, what resistor do I need as a pull-up on the gate of the QFET? Just a 10K, or is there a specific value?

magnethead494

Also, is a series gate resistor necessary in this application? If so, what value would be best?

raschemmel

#24
Jul 22, 2019, 08:07 pm Last Edit: Jul 22, 2019, 08:11 pm by raschemmel
If it were me I would just go with a simple solution:

With the right heatsink

this P-channel Mosfet could handle the 7.5A Bank1 an Bank2 easily

Datasheet



Bank1 => Mosfet-1
Bank2 => Mosfet-2
Bank3 => Mosfet-3


Parts:
qty: 3 FQP27P06 mosfet
qty: 3 TO-220 heatsink


The mosfets are logic level so you can drive them directly with an arduino output.
You might want to add 1k series resistor on each gate and 10k resistor from gate to GND.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

larryd

10k should work nicely.

A series gate resistor is needed if the Arduino was driving a MOSFET, this limits the Arduino output current to a safe level.

The 2803 is much more resilient.

BTW
It is always best to provide a proposed schematic as they are worth a billion words.







No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

larryd

You are right!  The datasheet is missing that critical detail.  The tab is almost always the same as the middle pin on any TO-220 package; they are presumably punched in one piece.

Mind you, that datasheet is actually from 2001 (down near the bottom).  That really is a rather poor device for your application, you would be much better off using a modern part requiring no heatsink.  If it is a SMD part, just use these adapters:

The chip plus the adapter will be no bigger than the TO-220 itself.  You will have a vastly more compact assembly.  :smiley-cool:

I like that.

Can add to the list for one of a kind wiring.







No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

magnethead494

#27
Jul 22, 2019, 08:44 pm Last Edit: Jul 22, 2019, 08:50 pm by magnethead494
Here is my current shopping cart.

I work 1 block from Mouser, so I'm going to call it into Will Call in the morning and pick up during lunch

https://www.mouser.com/ProductDetail/512-FQP27P06

https://www.mouser.com/ProductDetail/511-ULN2803A

https://www.mouser.com/ProductDetail/571-1-2199298-6

https://www.mouser.com/ProductDetail/603-CFR-25JT-52-10K

https://www.mouser.com/ProductDetail/279-CFR50J100R

https://www.mouser.com/ProductDetail/474-DEV-11113

https://www.mouser.com/ProductDetail/374-T5994ST

https://www.mouser.com/ProductDetail/855-M20-9992046

https://www.mouser.com/ProductDetail/755-BA07CC0T

raschemmel

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

larryd

Here is my current shopping cart.

I work 1 block from Mouser, so I'm going to call it into Will Call in the morning and pick up during lunch

https://www.mouser.com/ProductDetail/512-FQP27P06

https://www.mouser.com/ProductDetail/511-ULN2803A

https://www.mouser.com/ProductDetail/571-1-2199298-6

https://www.mouser.com/ProductDetail/603-CFR-25JT-52-10K

https://www.mouser.com/ProductDetail/279-CFR50J100R

https://www.mouser.com/ProductDetail/474-DEV-11113

https://www.mouser.com/ProductDetail/374-T5994ST

https://www.mouser.com/ProductDetail/855-M20-9992046

https://www.mouser.com/ProductDetail/755-BA07CC0T
All this can be shown in a schematic  ;) .




No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

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