[measure a voltage across of a dc motor]

hello,i am trying to measure a square wave(pwm) with amplitude 3V, so when i try to measure it with a multimeter across my motor,should i watch the next:

Vmultimeter=3*sqrt(duty cyle)

is it correct? because sometimes i am watching more than 3V on my multimeter across the motor about 3.7V but i think that it shouldn´t be higher than 3V.
i think that it can be caused about the inductance of the motor but i try to put a zener diode of 3V at the output of the AO but the problem is still happening.

somebody could help me with that? the Vcc=6V and the multimeter is set between the output of the power operational amplifier and ground

thanks

http://imageshack.us/photo/my-images/401/dudaq.jpg/

[pwm to control a dc motor]

if suply voltage is 5V and my duty cycle is 60%,the average voltage across my motor is 5*0.6=3V(max allowed)

so if i have the duty cyle 60% as i said ,why i can´t give a supply voltage higher than 3.5V,i want until 5V,
my motor won´t read more than 3V with supply=5 because my duty cycle is 60%

[pwm to control a dc motor]

http://imageshack.us/photo/my-images/705/sinttulo2mn.jpg/

i tried this circuit but with a transistor BD135 not a 2n2222A
and when i tried to supply the 555 with more than 3.5V,the motor consumes more than its maximum current allowed 0.3A
why is this happenin ?because my duty cycle is 60%(to get 3V across the motor)not 5V as i had with 100%duty cycle

[pwm to control a dc motor]

dc range

i don´t know if it takes the average or rms,which is the different?
the formula V=Vpeak*sqrt(duty) is with rms or average?

and i tried with a transistor BD135 but when the supply voltage for the circuit is higher than 3.5V the motor consumes its maximum current o.3V,why?

[pwm to control a dc motor]

the motor must be which i said you, i am gonna change the transistor to a BD135,which can have 1.5A at its colector
should it works?
and one question more:
when i check the voltages with my multimeter,i see the effective voltage ?
so to calculate the peak voltage the equation is :
Veff=Vpeak*duty cycle    or Veff=Vpeak*sqrt(duty cycle)

[pwm to control a dc motor]

MY MOTOR no load has 0.3A
and max efficient has1.05A
motor works between 1.5V and 3V max

in the datasheet of transistor 2n2222A:

0.8A max colector ,but we never have this value because we don´t have load(no gearbox) on the motor,so the max current will be 0.3A,YES?so it won´t be a problem?

and i saw too that total dissipation for 2n2222a is 0.5W at Tamb<25ºC and 1.8W at Tcase<25ºC,
so when we have the worst case P=V*I=3*0.3=0.9W, are we in the range,yes?

[pwm to control a dc motor]

and one question more

when the transistor is on cut-off which voltage is watching the motor,7V ? because the voltage maxium for my motor is 3V.
or it won´t affect because the motor doesn´t recieve energy?

[pwm to control a dc motor]

i tried it too, with that current but the same problem and when i try to see if the transistor is on saturation with the oscilloscope i see the next signal:

http://imageshack.us/photo/my-images/821/imageniqb.jpg/

[pwm to control a dc motor]

hello,i am trying to control a dc motor (1.5-3) with a transistor 2n2222a, at the 555output i have (supply voltage-1)=7-1=6V and the circuit is attached

my transistor has gain=40 and the maximum load of y motor will be 0.3A,so i need at my base a current at least I=0.3/40=7.5mA to get saturation, and the resistir at the base must be 6/7.5=800 maximum to get this, so i use a resistor=270ohm, all this is correct?

but the problem is that when i make the circuit, the transistor get so hot, why am i having this problem? how could i solve this problem?
pd: the diode on parallel with my motor is in correct way!

could somebody help me with this, i am really loss alot time with this but i don´t get a solution

thanks