Any ideas, best practices or suggestions for appliance of a MOSFET to prevent current

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Any ideas, best practices or suggestions for appliance of a MOSFET to prevent current drawn when APA102 leds are “off”?

Adafruit mentions some:

I’m using a Teensy or RFduino (so 3.3V), however I’ll use the 74HCT245 level shifter for Clock and Data. So I have some spare pins.

There a P and N variations. It seems that the N-type needs less circuitry around it. I draw at least 7A at a maximum.

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Hi,

That adafruit link is for “dumb” LED strips and so isn’t applicable to digital strips like APA102s.

You’ll need to use a P-channel MOSFET on the +5V line. If you get a logic-level MOSFET, you shouldn’t need any other components aside from perhaps a pull-up resistor on the gate of the FET to keep it turned off.

I don’t have a schematic handy, but the wiring would be: FET source goes to your +5V supply, FET drain to the +5V input of your strip, FET gate to your digital I/O pin. Pull the gate LOW to turn on the strip.

As for specific parts, I assume you want through-hole, not SMD. Try the NDP6030PL: https://www.fairchildsemi.com/datasheets/ND/NDB6030PL.pdf
If you want to look for others, search for “logic-level p-channel mosfet”. You want something with low on-resistance (aka “Rds(on)”), less than say 0.05 ohm. (e.g. at 7A and 0.05, your voltage drop is V = IR = 7*0.05 = 0.35V, not too bad)

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N channel on GND pin… a resistor on the gate in serie and another resistor to GND from the gate (to make sure it turns of)… Then your 3.3v will open the ground connection to your led’s.

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So as far as I understand the P mosfet is at the + side, so the ground is just normally connected to ground or not? @Tod_Kurt Why a P-channel is better?

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Hi @Kasper_Kamperman I have made a circuit with PNP MOSFET and a pushbutton. Startet a Wiki but I am not finished yet. If you use this logic IC everything works.

If you use another IC like SN74LS02N adjustments have to be made to the circuit.

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@Juergen_Bruegl Great explanation (my P v.s. N was answered as well). However I would like to use my Teensy/RFDuino to control the FET, so I think I won’t need that part of the circuit, or do I see it wrong?

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No, you don’t. Just a 2,2 - 10K Resistor between source and drain.
Make sure you are using a logic level PNP MOSFET as suggested in the wiki.
Haven’t tried it with Teensy (3.3V) - it should work because you are switching it ON by pulling the gate to ground.
Check whether the 3.3V are switching it completely off.

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@Juergen_Bruegl in the circuit the iRF7416PbF is mentioned as MOSFET but from the description it seems that you tried other mosfets is that right? Or did you test this one as well? It supports 7A, however there is no heatsink…

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The iRF7416PbF is a SO-8 type. For this you need a break-out board like this

Cost: 3$ + 2$ for the MOSFET
When you get a TO-220 like P-Channel MOSFET 20V 24A - low Vgs(th) - COM-12901 - SparkFun Electronics it is 2$ and you can put it directly on a strip board.
With 7A this guy won’t get hot and you need no heat sink. Attention: the metal lug on PNPs is +5V, don’t attach it to ground!

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I have been using an N-Channel on the negative side (DMN 3404L) with reliable results for small battery powered circuits using the APA 102C LEDs. This did not work for the WS2812 parts because you need to turn them on on the +side but so far it works on the APAs. I use ATtinys and put them to sleep at about .4ua and chose N-channels because I couldn’t figure out how to use P-channels and also keep the very low current sleep. I’d love to hear better ideas on this.

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@Daniel_Kaye you are pushin’ our luck - please take Adafruit’s advice seriously - it’s just like fighting gravity ;(
Maybe the small battery circuit save your sweet A…, because it has a high internal resistance.

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Finally I did a test with a Photon (3.3V output). I used this P-Channel Vishay mosfet: http://www.vishay.com/docs/67341/si4403cd.pdf

I noticed that 3.3V on the gate still doesn’t switch the power completely off (5V does). So that means I have to use a NPN transistor to switch between 5V and 0V isn’t it.

Any suggestions how I can select the right transistor? I’d like to put it later as SMD on a board.

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@Kasper_Kamperman select the right MOSFET like this one
http://www.digikey.com/product-search/en?mpart=FDS6575&vendor=261

more (look for 2.5V Gate drive) http://www.digikey.com/catalog/en/partgroup/p-channel-logic-level-gate-fets/16488?col=fet-feature&mpart=NDP6020P&vendor=261

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Thanks Juergen. I’ve found the FDS6576 with almost the same specs, but it’s a lot cheaper at Farnell then the FDS6575.

I’m curious if I can find that switching threshold without the special feature mention? I thought I had to look at the Gate Threshold Voltage, however those numbers are different than the mentioned 2.5V.
For example I’ve found the FDS6679AZ (https://www.fairchildsemi.com/datasheets/FD/FDS6679AZ.pdf), which mentions standard. How can I check in the datasheet if that fit’s my application?

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@Kasper_Kamperman you find it in the data sheet in Figure 2 (Drain Current vs. Gate Voltage). At 3.3V the line must cross your desired Amp rate.
The FDSS6679’ 3.3V line is not even on the chart. The FDS6575 does the 10A.

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I’m trying the FDS6576 now. However 3.3Volt is still seen as low. Only with 5V the mosfet switches off. So the result is the same as the Vishay I’ve tried before.

What would be the best solution then?

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are U sure? Do you have a resistor between gate and source (anything betw. 1K and 10K)?

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Yes, I have a 10K resistor between gate and source. So it’s completely off when I disconnected the Photon output. However connecting it to 3.3V it will be on. Connecting it to 0.0V as well (but that is supposed to happen).

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The data sheet says 2.5V …and on the part is
F P32DV
FDS
6576 ??
Did you solder it on a breakout?
U got a photo?