Electronics Forum

by **Naabish** » Thu May 16, 2013 5:28 pm

Well I have this circuit

[url=http://aijaa.com/DRBZie][img]http://i6.aijaa.com/t/00013/12225335.t.jpg[/img][/url]

And problem is that , the transistor doesnt do anything ( Q1) when I measured it with oscilloscope the the transistor doest do anything
PIC16F877A give PWM pulse from pin CCP1 to Q2 and same pulse is in R1 and R2 ?!

Question
- Should Q2 change pulses in R1 and R2?
- Should I put resistor before Q2?
- Why Q1 Doesnt change pulse?

Hope u guys understand my bad english but anyway
This is fan controller and take ideas from this

'http://www.electronics-lab.com/projects/motor_light/019/Schematic.png

by **pebe** » Fri May 17, 2013 10:16 am

Q2 has the output taken from the emitter, so no phase change takes place.
Q1 will invert the pulse, but you need a load fitted to the terminals.
Until you fit the load, you will only measure 0V at Q1 collector.

by **Naabish** » Fri May 17, 2013 1:00 pm

[quote="pebe"]Q2 has the output taken from the emitter, so no phase change takes place.
Q1 will invert the pulse, but you need a load fitted to the terminals.
Until you fit the load, you will only measure 0V at Q1 collector.[/quote]

Well do you have any idea , how I should fix this :shock:

Do i have to add something components before Q1 or Q2?

by **pebe** » Sat May 18, 2013 7:36 am

Connect a lamp, a motor, or any value resistor between the points marked + and - on the circuit.

by **Naabish** » Sat May 18, 2013 8:23 am

I had connect the Pc fan between + and - but fan speed doesnt change when I change PWM output from PIC16F877A.

by **pebe** » Sat May 18, 2013 10:46 am

But does the fan run?
If not, what is the voltage on Q1 collector?
Is there a 'scope waveform on Q1 collector? If so, what is the peak-peak voltage?

by **Naabish** » Sat May 18, 2013 3:36 pm

Fan didnt run , thats why I asking what problem my circuit have.
Hmm I think Q1 collector take 5 voltage but not sure because I didnt measure it by voltmeter yet :/
but when I measured it Q1 collector by oscilloscope it show Square wave , which its same
as PIC16F877A ccp1 output and Q2 collector input.

btw is Q2 doing right , does it have to change pwm output or not?

by **pebe** » Sun May 19, 2013 7:14 am

OK. Try this.

Remove wire between Q2 base and the PIC, and connect Q2 base to +5V.
Does the motor now run at full speed?
If not, measure the DC voltages at these points.

1. Q2 Base,
2. Q2 Emitter
3. Q2 Collector
4. Q1 Base
5. Q1 collector