Can anybody point me in the right direction on how to select the correct flyback diode for a small dc motor <1A (or any DC motor for that matter)? I've been searching and searching on several forums and am getting conflicting answers. Some say that the 1N4xxx type are fine as long as the voltage rating is at least 10x the motor voltage and at least the same current rating as the motor. Some say that a Schottky Diode must be used because of the fast recovery times needed with PWM like this one:
Also, how will a diode in parallel, like a counter emf diode, affect the voltage going to the motor? Does it reduce the voltage by ~.7V?
Also, how will a diode in parallel, like a counter emf diode, affect the voltage going to the motor? Does it reduce the voltage by ~.7V?
Since the diode is reverse biased, there will be no current flow.
Thanks Runaway Pancake,
Do I understand correctly that while the motor is in operation that there will be no voltage drop on the diode that is in parallel then?
That is correct.
When you stop driving the motor, the motor will try to keep the current flow going briefly, often with a nice voltage spike. The diode gives that current someplace to go.
From Wikipedia:
When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components.
TeslaIaint:
Thanks Runaway Pancake,
Do I understand correctly that while the motor is in operation that there will be no voltage drop on the diode that is in parallel then?
A diode in parallel with a motor experiences the same voltage as the motor. perhaps your question really asked "what current is taken by a diode wired in parallel with a motor" The answer is "zero" since the diode is reverse biased whilst the motor is being driven. Note however that, if you have a reversing circuit on your motor (by simply switching motor polarity), you will need to ensure the diode is switched also since it must remain reverse biased dependant upon the polarity applied to the motor.
Thanks all. That part of my question is answered.
Can anybody point me in the right direction on how to select the correct flyback diode for a small dc motor <1A (or any DC motor for that matter)? I've been searching and searching on several forums and am getting conflicting answers. Some say that the 1N4xxx type are fine as long as the voltage rating is at least 10x the motor voltage and at least the same current rating as the motor. Some say that a Schottky Diode must be used because of the fast recovery times needed with PWM like this one:
No need to agonise.
The diode's PIV should be greater (2X or so) than the motor voltage.
Get a rectifier diode, as opposed to a small-signal diode.
Schottkys are better at this, but 1N4**...** will suffice.
thanks again, Pancake. I'll use the Schottky Diodes first when my order arrives. Apparently the motor driver carrier has some internal flyback diodes, but I'd rather be safe than sorry. This is a prototype for a much larger project anyway where I'll be using larger motors, current, voltage, and of course higher value components. I'd like to get the programming and circuitry method down so I don't burn up the expensive stuff when it's time.