Transistor to drive a DC motor

[barf_soft]

ORKA
I found it
the correct circuit is the image that i attachad

see it

Tank all

 

[hameeds01]

ORKA
I found it
the correct circuit is the image that i attachad

see it

Tank all

is it working now??

 

[barf_soft]

I am sorry.
I make mistake.
It is worked well by changing the frequency of
motor
& i changed the program
to the following code

void main() {
TRISB=0;
while(1){
PORTB=0XFF;
Delay_us(800);
PORTB=0;
Delay_ms(2);
}

}

and it work well without diod
It is wonderfull
just changing the frequence period

the following code work WRONG
void main() {
TRISB=0;
while(1){
PORTB=0XFF;
Delay_ms(10);
PORTB=0;
Delay_ms(200);
}

}

Tanks hameeds01 for your reply

Added after 3 minutes:

It work well because of correct frequence
I dont know what is happened when the frequence
changed
any one know???

 

[barf_soft]

I found it!!!
the key is that we must use capacitor
parallely with dc motor
and IT WORK WITH EVERY FREQUENCE
I use 100uF capacitor paralelly with dc motor
and it work without nead of diod!!!
tanks All

 

[Audioguru]

Most transistors including the BD135 need a base current that is 1/10th the collector current for them to saturate well. Your base current is only about 4.9mA but the motor needs 690mA to start. With a collector current of 690mA then the BD135 needs a base current of 69mA which is much higher than the max 25mA allowed from a PIC and much higher than your 4.9mA. Use a darlington transistor.

 

[barf_soft]

First I must tell that the current for dc motor in direct use in 5V is 100mA and the hfe for BD135 in 100mA is ~ 55
100 /55 ~= 1.8 mA
and the Ic can supply this current and no nead for darlington
Ib*hfe=Ic
Ib base current
Ic collector current

Added after 2 minutes:

and the PIC can supply 1.8 mA

 

[Audioguru]

First I must tell that the current for dc motor in direct use in 5V is 100mA

Its starting current is much higher because it is stalled and is just the resistance of its windings.

and the hfe for BD135 in 100mA is ~ 55

hFE is used for a linear transistor that has plenty of Vce. When it is saturated it is spec'd with a base current that is 1/10th its collector current. Look at the datasheet for any transistor to see this.

 

[barf_soft]

OK
You are right
But when the transistor start to round
It is current is 50mA

Added after 6 minutes:

but it is not in saturation condition
and it is in hfe condition
I think
what is your opponion?

 

[Audioguru]

If your motor runs at 100mA then it might start at 500mA. Simply measure its resistance then use Ohm's Law to calculate its starting current.

The transistor must be saturated for it to be a switch. Then its base current must be 1/10th the collector current or some transistors will not drive the motor properly and those transistors will over-heat.

 

[hameeds01]

y don't u use Darlington pair transistor like TIP 120 ??

 

[barf_soft]

Your are right
the resistance is 3.6 ohms
5/3.6=1.38Amper
but the bd135 is not heated and it is cold
Tank you Audioguru

 

[Audioguru]

y don't u use Darlington pair transistor like TIP 120 ??

A darlington has 1.5V voltage loss and his supply is only 5V.
A logic-level Mosfet should be used.