I will be using driving N-channel Mosfets with 5v PWM to switch 24v 2A(per channel) LED strips. I will use four per strip (RGBW) and have 6 strips, totalling 24 Mosfets on the PCB.
I am looking at using the FAIRCHILD SEMICONDUCTOR FDD8878
- Transistor Polarity N Channel
- Continuous Drain Current Id 40A
- Drain Source Voltage Vds 30V
- On Resistance Rds(on) 0.011ohm
- Rds(on) Test Voltage Vgs 10V
- Threshold Voltage Vgs 1.2V
- Power Dissipation Pd 40W
- Transistor Case Style TO-252AA
- No. of Pins 3
- Operating Temperature Max 175°C
I have calculated the temperature rise to be 6°C
I x I x R = W
2 x 2 x 0.015 = 0.06W
Junction-to-Ambient thermal resistance = 100°C/W
0.06 x 100 = 6°C
Would this be a good choice Mosfet? Reliability and cool running without heat sinks is my main concern.
For comparison a SOT-23 Mosfet I was looking at:
- Transistor Polarity N Channel
- Continuous Drain Current Id 5.8A
- Drain Source Voltage Vds 30V
- On Resistance Rds(on) 0.03ohm
- Rds(on) Test Voltage Vgs 10V
- Threshold Voltage Vgs 1.2V
- Power Dissipation Pd 2.1W
- Transistor Case Style SOT-23
- No. of Pins 3
- Operating Temperature Max 150°C
The temperature rise for this would be: 14.4°C
2 x 2 x 0.036 = 0.144W
0.144 * 100 = 14.4°C
This would save a lot of space on the PCB, but I would be concerned that it wouldn't dissipate the heat adequately.