Diode for DC motors
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Posts: 46,084
DC Motor FET protection
Diode should be placed across DC motor and should be
forward biased by the current through the motor as a
result of the FET turning off. When the FET is on, the
DIODE is REVERSE biased and flows no current.
Diode PIV should be higher than the +vdc used on the
motor, so if your using 12 vdc to power the motor a 100
PIV (peak inverse voltage) is fine.
+vdc
Motor
N-FET
Gnd
| |
|
Diode|<|----|
With the diode being forward biased by the motor during
FET off time the power is dissipated across the motor
and the least amount of power is dropped across the
diode. Do not use a Zener in reverse bias as you will
drop too much power across the Zener.
www.digikey.com
Digikey part number HER302DICT-ND for example, others
are listed and the catalog page can be printed.
Is a 3 amp nominal forward current, 200 amp surge, 1
volt forward drop, 50 nanosecond reverse recovery time.
Only 0.65 cents each.
I would highly recommend using PWMpal to obtain a
stable uniform PWM pulse to send to the FET. You can
use a buss driver chip to drive the FET input if it is
a logic level FET. Place one 100 ohm resistor between
each buss driver and the common connection to the FET
gate. Use a 47K to ground on the gate input. By using a
buss driver chip to drive the FET now also have an
enable pin which can be used to enable or disable the
FET PWM signal.
Sincerely,
Ron Anderson
>
> Message: 1
> Date: Thu, 1 Jul 2004 17:40:30 EDT
> From: jcwale@a...
> Subject: Re: Using FETS on DC motors
>
> Can you suggest a "high speed recovery diode" to be
used with a MOSFET
> driving a motor (and source)?
>
>
> >No where in the previous messages did I see anyone
> >mention the need for a high speed recovery diode
across
> >the DC motor.
>
Diode should be placed across DC motor and should be
forward biased by the current through the motor as a
result of the FET turning off. When the FET is on, the
DIODE is REVERSE biased and flows no current.
Diode PIV should be higher than the +vdc used on the
motor, so if your using 12 vdc to power the motor a 100
PIV (peak inverse voltage) is fine.
+vdc
Motor
N-FET
Gnd
| |
|
Diode|<|----|
With the diode being forward biased by the motor during
FET off time the power is dissipated across the motor
and the least amount of power is dropped across the
diode. Do not use a Zener in reverse bias as you will
drop too much power across the Zener.
www.digikey.com
Digikey part number HER302DICT-ND for example, others
are listed and the catalog page can be printed.
Is a 3 amp nominal forward current, 200 amp surge, 1
volt forward drop, 50 nanosecond reverse recovery time.
Only 0.65 cents each.
I would highly recommend using PWMpal to obtain a
stable uniform PWM pulse to send to the FET. You can
use a buss driver chip to drive the FET input if it is
a logic level FET. Place one 100 ohm resistor between
each buss driver and the common connection to the FET
gate. Use a 47K to ground on the gate input. By using a
buss driver chip to drive the FET now also have an
enable pin which can be used to enable or disable the
FET PWM signal.
Sincerely,
Ron Anderson
>
> Message: 1
> Date: Thu, 1 Jul 2004 17:40:30 EDT
> From: jcwale@a...
> Subject: Re: Using FETS on DC motors
>
> Can you suggest a "high speed recovery diode" to be
used with a MOSFET
> driving a motor (and source)?
>
>
> >No where in the previous messages did I see anyone
> >mention the need for a high speed recovery diode
across
> >the DC motor.
>