Discussion in 'Math' started by 1213brett, Feb 9, 2015.

1. 1213brett Thread Starter New Member

Feb 1, 2015
13
0
I'm trying to find out if my mosfet needs a heat sink. my load draw 1.20 A and im triggering the mosfet with ardino pin 7 5V

P= current squared * RDS
1.20 A * .16 Ohms squared = .2302

TJmax - Tambient / ROJA
150 - 25 / 62 = 2.02

2.02 is larger then .2302 so I need a heat sink

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Last edited: Feb 9, 2015
2. ScottWang Moderator

Aug 23, 2012
5,429
854
You can choosing some other mosfets has lower Rds then it could reducing the power consumption.

3. Magician New Member

Aug 18, 2014
13
6
No, you don't. MOSFET is o'k up to 2W w/o heatsink, and it's needs to dissipate 0.23W. Are you using PWM? Losses may be more in case PWM

4. 1213brett Thread Starter New Member

Feb 1, 2015
13
0
No I'm not. And thank you!

5. WBahn Moderator

Mar 31, 2012
20,057
5,651
Note that
150 - 25 / 62 = 149.60

Remember order of operations!

If you mean (150 - 25) / 62, then say so.

Pmax = (TJmax - Tambient)/ROJA = (150 °C - 25 °C)/(62 °C/W) = 2.02 W

Pactual = I²·Rds = (1.2 A)²·(0.16 Ω) = 0.23 W

Since Pactual < Pmax, no heat sink needed.

6. uwed Member

Mar 16, 2015
64
17
Rds=0.16 ohm is usually normalized (room temperature). If you operate at Tj=150°C we would have Rds=2.2*0.16=0.35ohm (see Fig.4 in the datasheet).