MOSFET for Art & Design - Page 1
Forum section: electronics / projects

author: unknowndomain
author_rank: Regular Contributor
timestamp: June 13, 2018, 10:21:18 pm
content: I work in a design school in London, where we support students with electronics and coding projects, and we used to buy the Arduino TinkerKit MOSFET modules for about £6, these were great because they were really robust for students.Unfortunately Arduino won't open source the product and won't manufacture any more either, leaving anyone who bought the TinkerKit products up the creek without a paddle, however luckily we just use these modules without the rest of their system using some normal M-F jumper wires.Anyways, I wanted to look at designing an alternative module myself that we could open source, the only similar items I've found are basically a breakout board, and this is a bit more than that...It has:Power LEDLED for status3.3v/5v InputPins for power in and out, rather than just the negative and sourceReverse input protectionI am going to start working on this myself, but would love some input and ideas before I start, even part suggestions for reasonable quality, cheap MOSFETs etc...I am currently aiming for up to 30V/5A as we don't carry power supplies more beefy than that and will probably look to put a barrel jack rather than screw terminals as we use these with 2.1x5.5mm jacks anyway, so may as well be PCB mounted.Anyway thoughts appreciated...

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2018, 10:26:03 pm
content: It sounds simple enough that you could just reverse engineer one of the existing devices and build more of them?

author: unknowndomain
author_rank: Regular Contributor
timestamp: June 13, 2018, 10:32:04 pm
content: I started doing this a while back, I realised the main things going on here are:1. Power LED: LED + current limiting resistor calculated for good illumination as 3.3V or 5V2. Output LED: LED + current limiting resistor3. Reverse polarity diode4. Back EMF diode5. A couple of capacitors presumably for decoupling?6. IRFS3806 transistorBut I can't figure out what the SMD DIL package is, I don't have the part number to hand but nothing came up doing some googling.

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2018, 10:34:11 pm
content: I would expect it to be a mosfet gate driver, but if you draw up a schematic of the board it should be reasonably apparent what the mystery part is doing.

author: unknowndomain
author_rank: Regular Contributor
timestamp: June 13, 2018, 10:36:22 pm
content: I'll get on that tomorrow.I my knowlge around MOSFETs is a bit weak, I'll do some looking up about what a gate driver is and does, that should help.

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2018, 10:47:54 pm
content: A gate driver drives the gate, duh.On a more serious note, in a nutshell the gate of a mosfet is capacitive so if you need fast switching like for PWM, you need to be able to drive it fairly hard to charge and discharge the capacitance quickly. It also typically has to be driven to a voltage higher than 5V to saturate the mosfet, so many gate drivers incorporate logic level translation.It's possible that the IC is something else, perhaps current sensing, but again with a schematic it will be easier to guess what it is.

author: unknowndomain
author_rank: Regular Contributor
timestamp: June 13, 2018, 10:49:42 pm
content: CheekyI'll It's 23:49 here in London, will try and buzz out the connections tomorrow morning.

author: Leiothrix
author_rank: Regular Contributor
timestamp: June 13, 2018, 11:40:54 pm
content: Have you had a look at the various Chinese online shops? Here's one from banggood, I just searched for "arduino mosfet"https://www.banggood.com/10Pcs-DC-1-Channel-1-Route-IRF540-MOSFET-Switch-Module-For-Arduino-p-1204945.html?rmmds=search&cur_warehouse=CN

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 14, 2018, 01:28:45 am
content: Aren't there lots of reasonably cheap MOSFET modules out there for 3D printers?

author: unknowndomain
author_rank: Regular Contributor
timestamp: June 14, 2018, 01:21:26 pm
content: So I had a look at a couple of them and the newer ones are very similar, but the unknown component has changed (pin for pin match tho) this is an MV3581 low voltage rail to rail op amp.I've drawn it out here, does this look like it makes sense to folks?

author: madires
author_rank: Super Contributor
timestamp: June 14, 2018, 02:25:45 pm
content: A quick search reveals a IRF520 MOSFET and a LMV358 dual OPamp. Seems to be a quite simple circuit with one OPamp driving the MOSFET and the other one driving the LED. Driving the IRF520 with a V_GS of nearly 5V isn't ideal (10V would be much better) and they could have added a reverse input protection for +5V with a small p-channel MOSFET. The design is a bit disappointing. I'd replace the MOSFET with a logic level type or replace the LMV358 with a gate driver, and also add a p-channel MOSFET based reverse input protection for the 5V rail.