controlling voltage is higher than required operation voltage

[Vraj]

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?

 

[srizbf]

possible.
What is the current spec of the motor?

 

[KlausST]

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

 

[Vraj]

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 ?

 

[KlausST]

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

 

[Vraj]

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

 

[KlausST]

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

 

[Vraj]

Hmm,
So i will require npn and pnp transistor,
And why they are showing pwm and inverted pwm as input?
Do i require both inputs?
https://e2e.ti.com/cfs-file/__key/c...ponents-weblogfiles/00-00-00-07-88/1184.3.jpg

 

[KlausST]

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