I try to power a high power lamp through a MOSFET driver. Does anyone know a breakout board with a MOSFET driver capable of passing through that much power. As far as I know above 1A there is usually the need to have a heat sink. In case of a maximum current of 6.25A the heat sink has to be massive I guess. Has anyone driven such a load already and has a hint w.r.t. breakout board and heat sink.
Is your lamp an incandescent or LED lamp? Are you just wanting off/on control, or light intensity control as well?
It is about the Rds_on, the resistance when the mosfet is turned on.
Adafruit has this logic level mosfet: https://www.adafruit.com/product/355.
Suppose you drive the gate with a 5V Arduino board and the current is 6.25A and it is at room temperature.
Then Rds_on is 10 mΩ and the mosfet has to dissipate 62.5 mW.
If you want to control the intensity as @Paul_KD7HB wrote, then the switching of the PWM signal can make it hotter. That mosfet from Adafruit has a capacitance of the gate of 1nF.
@Paul_KD7HB It’s a Incandescent lamp. I want to dimm it. Cause it’s a halogen lamp the minimal current required to get it started is quite high (between 2.5 and 3 amps).
I’ve attached a heat sink on top of the mosfets of my current breakout board. My current power supply is limited to 5 amps but dimming is working. RIght now the rds_on seems to be ok. Could break the rds_on after some time?
In that case, all the power you are NOT sending to the lamp must be dissipated by the mosfet and the heat sink.
Not completely open mosfet will be hot, PWM is opening it completely so it is applied 62.5 mW calculation, changing PWM pulses width will dim the lamp.
You need to appreciate the implications of this:
I can add a little more to that.
The Arduino output pin should be current limited with a resistor, because a PWM into a capacitor is not nice. The resistor with the internal gate-capacitance becomes a RC filter, that slows down the slope of the signal, so the mosfet will spend more time between on and off.
The disadvantage of a mosfet is that when it is heating it up, it heats up more.
Suppose the temperature rises to 125°C. Then the Rds_on is no longer 10mΩ but 15mΩ, so it heats up more.
I’m using the datasheet of the IRLB8721PbF that Adafruit has. Many other mosfets have a higher Rds_on.
Have you dimmed the load using the PWM using a little value, let's say 1%? In my setup the MOSFET driver + too little heat sink is overheating as soon as I dimm the load a lot. In this case a lot of energy is converted in heat.
This circuit has no option to regulate width of the PWM pulses.
You are using mosfet as a regulated resistor, to dim 150W load by 50 % you have 75W on load and 75W on mostet which is 50% open.
PWM is switching on/off mosfet 99.5%, total time = 50% on and 50% off, so you hawe only 62.5 mW converted to heat for 50 % of the time.
You need PWM program with regulated pulse width or
plus 1k resistor on gate