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controlling voltage is higher than required operation voltage

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Vraj

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i have 5v pwm output as controlling voltage of 3.3 v motor!
i also have to use driver for higher current.
i am confused!
which transistor should i use?
will inductor or capacitor require?
 

possible.
What is the current spec of the motor?
 

Hi,

If you limit the RMS current then you should be safe from overheating.
If you limit the average voltage then you should be safe from too high RPM.
(for a full bridge driver: limiting the duty cycle to 66% should be safe. 5V x 66% = 3.3V)

Klaus
 

Hmm, my motor's current rating is 0.8 amps.

- - - Updated - - -

And what about the driving circuit? I have learned that p channel transistor is good for fast switching but, will it invert the duty cycle ?
 

Hi,

For a motor RPM control I recommend to use a half bridge.
Then duty cycle to RPM is about constant.

Look at motor driver IC manufacturers or distributors for motor driver ICs or half bridge.

Klaus
 
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    Vraj

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ok, but why there is two transistors?
can't work with 1 only?
 

Hi,

A single transistor will work. But expect low torque. --> RPM is not very constant with varying load.
With ohmic loads this is not the problem, but the motor is partely inductive.

Klaus
 

Hi,

if they were not inverted, then both MOSFETs are ON at the same time --> causing short circuit.

Look for a - ready to buy - motor driver, they usually are more rugged because of internal protection functions and they are easy to use.
I don´t recomend to build one with discrete parts.
Building a discrete one often takes more time, is not cheaper, causes more trouble.

Klaus
 

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