as some may know i have been designing a product that has a lot of customisation options.
i require a 5 output switching mosfet or the best small mosfets that can handle 1A @ 3.4-5V and switch effectively at high speed(.20s+), im also trying to minimalize the EMI.
I have a few to test with
1E32AA FQP30N06L
3B18AR FQP50N06
and a random one i pulled form misc electronics
MC 7815CT RXX 750 G
Hi,
What do you think a "MC 7815CT RXX 750 G" is?
That is a 5Volt Linear regulator, so it will not help you switching LEDS.
If you aim to control the MOSFETs with the Arduino output you will need "logic level" MOSFETs.
What Arduino are you using.
Can you post the spec/data of the MOSFETs you have chosen?
Thanks.. Tom.. 
High amp LEDs usually require constant current LED drivers, not mosfets.
What sort of LEDs are we talking about.
Leo..
DC forward voltage (VF):
White: 3.0V-3.4V
Red: 1.8V-2.4V
Green: 3.0V-3.4V
Yellow: 1.8V-2.4V
Blue: 3.0V-3.4V
Forward Current: 700mA /LED CHIP
Most of us already know Vf of LED colours.
700mA is a little over 2watt per LED, so we're talking 3watt LEDs.
Are you going to use single LEDs, powered from 5volt.
Or strings of LEDs, powered from 12volt or 24volt (like in your previous threads).
Leo..
which ever is most efficient, its a 12VDC power source. either i can run them as 3-4V in parallel or run them as 12-14v in series.
im assuming in each id have to have a different regulating circuit to maintain constant current and another to provise a constant power source even when a vehicle 12v fluctuates between 12-14.5v
im assuming in each id have to have a different regulating circuit to maintain constant current and another to provise a constant power source even when a vehicle 12v fluctuates between 12-14.5v
LEDs require a constant-current source and the voltage "falls into place". The constant-current supply needs to supply sufficient voltage (and power) but otherwise it should "just work". For rexample, [u]this 12W, 700mA power supply[/u] will happily drive one 3W LED, or four 3W LEDs in series, supplying a constant 700mA.
which ever is most efficient, its a 12VDC power source. either i can run them as 3-4V in parallel or run them as 12-14v in series.
If you are powering multiple LEDs from the same driver/power supply, they MUST be in series because that's the only way to insure the current is the same through all LEDs.
But of course, if you are using RGB LEDs you can't wire them in series because there are only 4 wires for 3 LEDs.
But of course, if you are using RGB LEDs you can't wire them in series because there are only 4 wires for 3 LEDs.
This doesnt make any sense to me. if im wiring them in series they could just go into each other no?
i have 9 leds so lets say 3X3 so if i get a 2.1A X 12V CC power supply i could do that? would just have to push 700mA x3 and 3.4v x3 no?
they are not common anode or common cathode
If you are using single 3watt LEDs on a star base on a 12volt supply, then it's best to use three of them in series.
A mosfet switch + current limiting resistor can be used, but the resistor will get hot and LED brightness could vary.
Better to use a switching constant current LED driver.
No mosfet needed, and you can PWM these modules with an Arduino.
Those modules could produce some EMI, but so could a mosfet/resistor.
A metal enclosure and/or ferrite beads might be needed.
Cross that bridge when you get there.
Leo..
okay so im just going to roughly look at what ill need.
9 leds in total, each one is a 5 color led, ive mentioned this before in other topics long ago,
i need to be able to address each set of 9 leds to work as a single "led module"
it will have an 12-14VDC in for power will need to regulate that i presume, then a driver for 5 colour modulation form the MC. outputting to the 3x3, 700mA leds.
questions
need to get a move on and get this prototyped so i can start to trail and error, but i dont know where to start XD
cminke:
9 leds in total, each one is a 5 color led
What LEDS are you talking about ?
Post a link or a part number or something.
Without knowing what they are, everyone just has to randomly guess what sort of circuit you'll need.
Yours,
TonyWilk
cminke:
i require a 5 output switching mosfet or the best small mosfets that can handle 1A @ 3.4-5V and switch effectively at high speed(.20s+),
Firstly there is no "best" unless you define exactly how important each requirement/desired property is
relative to all the others, and there are lots of things that might be important:
static losses (ie maximum on-resistance)
dynamic losses (ie switching speed)
max power dissipation
package size,
max supply voltage
gate drive voltage (logic level, 3.3V or 5V, etc)
price...
"0.20s+" - how is this high speed? "<= 100ns" is a speed specification. No MOSFET is too slow to switch LEDs, they all switch sub-microsecond if the gate is driven suitable
Anyway if you want to minimize EMI you don't want high speed at all, you want to deliberately slow the switching, which is going to be a compromise with dynamic switching losses...
Don't forget about constant current linear regulators - they provide constant current regulator and are simpler to build (if you're making your own board) - just the chip, a decoupling cap, and a resistor to set current (AMC7140 - up to 800mA, with a pin you can PWM to dim it, so you don't need external mosfet), though they have the power efficiency of a resistor, ie, the extra voltage is dissipated as heat.
The dirt cheap AMC7135's work for 350mA LEDs (fixed current), and you can switch the low side with a MOSFET just fine. You can even use them to drive 12v LEDs this way by using a zener diode and resistor to generate the ~5v operating voltage (you can't drop that much voltage across them, though).
You can use resistors with 1 and 3 watt leds, but you need fairly beefy resistors, because you need to drop a couple of volts through them to keep the current from fluctuating too much with temperature (since LED Vf drops as they get hotter).
Switchers, as noted above, provide highest efficiency and great current regulation, but are more expensive and require more design effort to build your own (though modules are available from the usual cheapo chinese sources)
As for MOSFETs, there are a lot of stunningly capable MOSFETs in SOT-23 for currents up to a few amps (mfg specs cap out around 6A for logic level FETs in SOT-23, though you never want to use a part right at the top edge of it's spec). For larger loads, I default IRF3708 - works with 3.3v logic, and handles tens of amps with low Rds(on).
Awesome guys lots of good information. Keep it comming and I'll keep feeding back!
So I could use a sot-23 style fet with 3*700mA(2.1A) no problem!
Any recommendations. It's going to be locic level I believe.
Should i have a singular cc regulator or have one for each led bank?
I'm looking at microcontroller options as well each module will have its own to receive information from a master, retain memory, comunicate with other modules and control the fets/switching controller.
My master controller is going to be based off the Arduino 101/Intel curie. If you have other recommendations let me know !
