pwm 7.2v motor
Hi there,
As I said at the top, I am still learning so please bear with me.
I have taken out the opto coupler for now and are testing just with a BC337 transistor but it does not work as I think it should. The 18.1 V gets generated from a max622 voltage pump from 7.1 V which generates VCC + 11V.
The BC337 I have has a Hef of 338. So the maximum allowed current through the transistor would be
I = V/R * Hfe = ((5-0.7)V/0.019A) * 338 = 6.6A
This is way above what the 150R resistor would allow.
I = V/R = (18.1 - .7)/(10K + 150R) = 120mA
According to my calculation now the current through the transistor would be
I= V/R = (18.1-.7)/(10K + 150R) = 1.7mA
But if I measure at the emitter of the transistor I should get
V=17.3 * (10k/(10k + 150r) = 17.044V
if the transistor is driven to saturation.
Well, My PWM signal is perfect just after the 220R resistor and measures about 4.2V at the base of the transistor.
But when I measure at the transistor's emitter I find that I get more or less the same voltage as at the base of the transistor. I still see the PWM signal but it levels out at about 4.2 - 4.4 Volt. Why do I not get an 17V PWM signal?
I am a self taught person so if I am not doing things right please let me know. What must I do to drive a MOSFET in this configuration?
Regards
Nic