enchance dc motor driver circuit.

hi all,
below is my driver circuit for controlling motor. the pin1 of optocoupler or 4n25 is connected with my arduino( the arduino giving pwm signal to the optocoupler). the circuit works fine and motor is rotating but not at full speed eventhough i set arduino(microcontroller) to "255" value which the maximum speed". I believe the current is not enough to run the motor at full speed and the motor supply i use is 9V. the motor i m using is motor from a helicopter toy. I could not determine the rated current because i bought the toy helicopter itself thus there is no datasheet on the motor. So member i would to know how can enhance this circuit ? Moreover during hardware implementation, for optocoupler base terminal i didnt connect to ground because when i connected to ground the circuit wont works. Besides that, If i change 4n25 to 4n35, what will happen? TQ**broken link removed**

I don't see an attached file or image? This could be because I am at work.

Ron

Duplicate Post, Please ignore

Why is the base of the photo-transistor grounded?

The 1K gate resistor looks too low to me. The 330Ω in series with the photo-emitter will limit the current to (5-0.5-1.5)/330 = 9mA. The Current Transfer Ratio for the 4N25 can be as low as 10%, meaning that the current through the gate resistor would be about 1mA, which would only make 1V at the gate; hardly enough to turn on the NFET.

The PIC pin can source ~20mA, so cut the 330Ω to 150Ω. Raise the gate resistor from 1K to 3.3K.

Even at that, it is still a crummy gate driver.
A proper gate driver for this FET should source/sink ~250mA in order to switch it on/off fast. Even with the changes suggested above, your are driving the gate with ~few mA. It might work if the PWM rate is slow enough (100Hz)