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edited Nov 22, 2016 at 13:38

I have constant current source circuit as follow:

The mosfet chosen is: Fairchild Semiconductor FCH072N60F Fairchild Semiconductor FCH072N60F (Q1, Q2 are identical). Digikey link: http://www.digikey.com/product-detail/en/fairchild-semiconductor/FCH072N60F/FCH072N60F-ND/4022750

For anyone questioning the 500 Ohm gate resistance: I have to increase gate resistance to dampen mosfetMOSFET ringing (it gets pretty bad when Rg < 100).

My ultimate purpose is to generate a sinusoidal constant current (with Vpeak/2 DC offset) with this circuit. But for now, I use a 10V Vgs, 5A DC current for the sake of thermal analysis (input of the op amp is 5V DC). The phenomenon is the the MosfetMOSFET is much hotter than the series resistance (R26). I think this suggests that Rds of the mosfetMOSFET are higher than 1 Ohm, which is not possible because the datasheet states that Rds = 0.06 Ohm to 0.07 ohm when Vgs = 10V.

I guess that the gate resistance Rg has something to do with this but changing Rg didn't help.

I have constant current source circuit as follow:

The mosfet chosen is: Fairchild Semiconductor FCH072N60F (Q1, Q2 are identical). Digikey link: http://www.digikey.com/product-detail/en/fairchild-semiconductor/FCH072N60F/FCH072N60F-ND/4022750

For anyone questioning the 500 Ohm gate resistance: I have to increase gate resistance to dampen mosfet ringing (it gets pretty bad when Rg < 100).

My ultimate purpose is to generate a sinusoidal constant current (with Vpeak/2 DC offset) with this circuit. But for now, I use a 10V Vgs, 5A DC current for the sake of thermal analysis (input of the op amp is 5V DC). The phenomenon is the the Mosfet is much hotter than the series resistance (R26). I think this suggests that Rds of the mosfet are higher than 1 Ohm, which is not possible because the datasheet states that Rds = 0.06 Ohm to 0.07 ohm when Vgs = 10V.

I guess that the gate resistance Rg has something to do with this but changing Rg didn't help.

I have constant current source circuit as follow:

The mosfet chosen is: Fairchild Semiconductor FCH072N60F (Q1, Q2 are identical).

For anyone questioning the 500 Ohm gate resistance: I have to increase gate resistance to dampen MOSFET ringing (it gets pretty bad when Rg < 100).

My ultimate purpose is to generate a sinusoidal constant current (with Vpeak/2 DC offset) with this circuit. But for now, I use a 10V Vgs, 5A DC current for the sake of thermal analysis (input of the op amp is 5V DC). The phenomenon is the MOSFET is much hotter than the series resistance (R26). I think this suggests that Rds of the MOSFET are higher than 1 Ohm, which is not possible because the datasheet states that Rds = 0.06 Ohm to 0.07 ohm when Vgs = 10V.

I guess that the gate resistance Rg has something to do with this but changing Rg didn't help.

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asked Nov 22, 2016 at 9:47

HacLe

Mosfet based constant current source, and the mosfet gets too hot

I have constant current source circuit as follow:

The mosfet chosen is: Fairchild Semiconductor FCH072N60F (Q1, Q2 are identical). Digikey link: http://www.digikey.com/product-detail/en/fairchild-semiconductor/FCH072N60F/FCH072N60F-ND/4022750

For anyone questioning the 500 Ohm gate resistance: I have to increase gate resistance to dampen mosfet ringing (it gets pretty bad when Rg < 100).

My ultimate purpose is to generate a sinusoidal constant current (with Vpeak/2 DC offset) with this circuit. But for now, I use a 10V Vgs, 5A DC current for the sake of thermal analysis (input of the op amp is 5V DC). The phenomenon is the the Mosfet is much hotter than the series resistance (R26). I think this suggests that Rds of the mosfet are higher than 1 Ohm, which is not possible because the datasheet states that Rds = 0.06 Ohm to 0.07 ohm when Vgs = 10V.

I guess that the gate resistance Rg has something to do with this but changing Rg didn't help.

mosfet