A small MOSFET Driver PCB: What do you think is required?

Cluso99

I accidentally posted this in the wrong forum. I have deleted it and reproduced it here.

I have the basics of a MOSFET driver I require for a project.

As with any design, I always try to think of what else it could be used for, and create options on the pcb for other such uses.



Here is what I have spec'd...

• Up to 25V 15A (limited by connectors/pcb)
• 4x Screw power connectors http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=8191K-ND
  • 2 Power input V+ and Gnd
  • 2 Power output V+ and V switched
• Small MOSFET N Channel ~30V 70A low Rdson
• Drive inputs via 2pin header (Drive, hi = on; and Gnd) by either
  • transistor input (series 2K2 input to base with 47K base to gnd)
  • optoisolator input (series resistor to led, then gnd)
• PCB may fit a Hammond 1551 box ??? Is this required?
• PCB could be as small as 1"x1" or 1.2"x1.2". Does it matter?
• Possibility to daisy-chain up to 4? (i.e passes unused inputs to next in chain)

One of the uses is to control a heated device.


I have proposed a poll to ask a few questions.

Cluso99

(copied from the thread I deleted)

agimuhing wrote: »

I chose dumb, the propeller can handle controlling motors while analyzing sensor data. If I wasn't using a micro as capable at multitasking as the prop I would choose intelligent to reduce processor load.

frank freedman

I would vote dumb for max flexibility. Feedback sensor? For xyz type of sensor. Just reduced the flexibility of the PCB to a small family of apps. I was tempted to vote multiple on one board, say multiples of two or four for totem pole or H-bridge drive circuits.

smbaker

I chose 'dumb' and 'multiple'. If you want a smart solution, you can always add an intermediate board between the prop and mosfets.

For screw terminals, I've really taken a liking to two-piece terminal blocks like this kind:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A98229-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A98427-ND

The ability to be able to unplug all of the loads at once I've found pretty handy, especially on boards with many connections (like a multiple-mosfet board).

JonnyMac

I tend to do a lot of LED lighting (props and displays in "Hollywood") and many high-power RGB LEDs are common-cathode only, hence I would suggest/like to see a high-side output. I'm working on my own board anyway, and that's the direction I'm taking. I'm also using a Microchip TC4427 between the Propeller and the MOSFET so that I can drive it at very high frequencies.

PJAllen

I accidentally posted this in the wrong forum. I have deleted it and reproduced it here.

You missed the mark this time, too.

kwinn

I wonder if it would be possible to design it as an H bridge driver in a manner that would also allow it to be used as a low side or high side driver. It would also be good to have it handle higher voltages ( 200V ? ) so it could be used with line powered equipment.

I know i'm asking for a lot, but hey, if you don't ask you never get.

Cluso99

All, thanks for the feedback so far.

Perhaps I should explain a little further...

I have a stepper driver pcb for my RepRap design using plug-in modules (I have an equivalent/compatible to the Pololu A4983/A4988 which I based on the A4982/A4984). Pcbs are in transit.

I now require driver modules for the Extruder and Heated-Bed (temperature control). They must be cheap in case of failure. Due to the high currents, it is not really feasible to make them the plug-in style like the stepper drivers. Therefore, the power in and out connectors must be on the "disposable pcb". I chose a relatively cheap connection that can use the crimp ring or "u" connectors - most people have these automotive crimps and the tool, or access to them. Currently the pcb design looks like 1"x1" or 1.2"x1.2" for a single MOSFET. Pcbs can be daisy-chained.

To minimise the heat dissipation on the pcb, I have chosen a reasonably-priced N channel MOSFET SOIC-8 sized with very low Rdson of ~3mohm. Now, to turn the MOSFET on fully, a prop will not achieve this directly without increased heat. So, I am using a dual NPN & PNP transistor with inbuilt biasing resistors in a tiny SOT23-6 package. I intend to also provide optional provision for an optoisolator as well. Switching will be via the ground leg.

Out of interest, my searches revealled very few P channel MOSFETs in TO220 t/hole packages. P channel MOSFETs currently have larger Rdson values, and a much more limited range.

For my quadcopter design, I will be producing an ESC equivalent to drive each BLDC motor. This will have 3 sets of N and P channel MOSFETs.

JonnyMac: Yes, the TC442x family are a nice set of drivers. Bit $ for my needs. A single NPN and P channel MOSFET would do a high side switcher quite efficiently.

Kwinn: Higher voltages use much larger package MOSFETs. I also wish to be careful in providing a pcb that could result in use of lethal voltages by the unwary.

Cluso99

I have had a rethink about using a P Channel MOSFET. Here is a potential circuit.

I think R3 should be at least 1K and R4 is probably not required.
The Mosfet most likely is a AOD403 http://www.aosmd.com/res/data_sheets/AOD403.pdf