B
Bart
- Jan 1, 1970
- 0
Dear,
I have a question about paralleling hexfets.
I already searched a lot, but I did not find yet the rigth answer to
my question.
Let me explain what I want to do:
I created a circuit to drive four fans. (I want to regulate the fans
RPM) Explained in short it is as follows:
The gate of my FET is driven by a fan driver (MAX 6651), the source is
connected to ground and the drain is connected to the first wire of
the fan, the other wire of the fan is connected to 24V.
So by regulating the voltage at the gate, the 24V power voltage is
divided in 2 parts, one part is over the fet (Vds) the other part is
over the fan.
If I connect four fans to 1 fet (which is theoretical right) there is
a lot of heat dissipated in the hexfet. I measured temperatures of
130 °C. So I thougt to place four fets in parallel. Then the current
would divide into 4 equal parts and the dissipated heat in the fets
will decrease.
By measuring temperatures after placing them in parallel, the result
is as follows: One fet is getting very hot (120°C), 2 other fets
about 70°C and the fourth has 40°C. How is this possible?
I tried already several things. I tried with 2 fets. Then the first
ons has 100°C and the second 75°C. On the internet I found that you
have to place serial gate resistors (typical value = 100 ohm) when you
place fets in parallel. Also when I try this, the temperature does
not decrease.
Question: is there anyone who can tell me what I am doing wrong. I
would like to have a circuit by which the maximum temp is about 40 or
50 °C (instead of 120 °C). The number of fets doesn't matter.
Is it useful to place a serial source resistor?
If so, what is the typical value about that?
Please can anyone help me?
I have a question about paralleling hexfets.
I already searched a lot, but I did not find yet the rigth answer to
my question.
Let me explain what I want to do:
I created a circuit to drive four fans. (I want to regulate the fans
RPM) Explained in short it is as follows:
The gate of my FET is driven by a fan driver (MAX 6651), the source is
connected to ground and the drain is connected to the first wire of
the fan, the other wire of the fan is connected to 24V.
So by regulating the voltage at the gate, the 24V power voltage is
divided in 2 parts, one part is over the fet (Vds) the other part is
over the fan.
If I connect four fans to 1 fet (which is theoretical right) there is
a lot of heat dissipated in the hexfet. I measured temperatures of
130 °C. So I thougt to place four fets in parallel. Then the current
would divide into 4 equal parts and the dissipated heat in the fets
will decrease.
By measuring temperatures after placing them in parallel, the result
is as follows: One fet is getting very hot (120°C), 2 other fets
about 70°C and the fourth has 40°C. How is this possible?
I tried already several things. I tried with 2 fets. Then the first
ons has 100°C and the second 75°C. On the internet I found that you
have to place serial gate resistors (typical value = 100 ohm) when you
place fets in parallel. Also when I try this, the temperature does
not decrease.
Question: is there anyone who can tell me what I am doing wrong. I
would like to have a circuit by which the maximum temp is about 40 or
50 °C (instead of 120 °C). The number of fets doesn't matter.
Is it useful to place a serial source resistor?
If so, what is the typical value about that?
Please can anyone help me?