Troubleshooting a fan speed controller UPDATE

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,260
Yes, that looks like mine with the exception you're using pin 7. The reason why I thought it was correct to use pin 3 is because I thought (maybe in error) that using pin 7 would mean the clock pulse would go from zero (or near zero) to 50%. No???

I think I've looked at my diagram and figured it wouldn't work because at initial power on pin 3 would be at ground, and thus, the cap would never charge. I've been developing a PWM using a CD4011BCN. I think the drawing I've made would work the way I want it to. But so far all I've done is drawings. No materials have been committed to solder.
 

shortbus

Joined Sep 30, 2009
8,057
You still trying to use stuff you found? I started out doing that but through it all away because it never worked for what I was trying make.

Pin 7 has to do with discharging the internal cap in the 555 - https://www.dummies.com/programming...nics-components-how-the-555-timer-chip-works/

Pin #3 only sinks, it can never source to drive your gate you need a way to do both.

Look at the circuits Wendy has posted here on PWM. https://forum.allaboutcircuits.com/threads/submission-555-pwm-oscillator.24028/ There may be more by her.
 

MisterBill2

Joined Jan 23, 2018
7,322
The PWM circuit that worked very well use the second timer on a LM556, which is a dual 555, as a comparator Then a small transistor to drive a larger power transistor to drive a DC motor. It was more stable, and it held a constant frequency, and it was able to go from 0% to almost 100% in a quite linear control manner. Source or sink? All you need to do is look t the internal circuit of the 555 in a data book to clearly see which it is. You find that the discharge , pin 7, is an NPN to common, while the output has both source and sink transistors.
 

shortbus

Joined Sep 30, 2009
8,057
Since when? The datasheets show output voltage-drop curves sourcing up to 100mA.
I have been under that assumption for a long time, some one on a forum told me that years ago and I have assumed he was correct. Should have looked at a data sheet to see he was wrong.

When doing projects like this PWM, I just get one ready made from Ebay, can't make a PCB and buy the parts and build one for what they sell them for. Add my own mosfet for the volts needed and I'm good to go.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,260
Here's an update on this silly and slow to happen project:

I've ditched the idea of using the PWM module from the Toyota and opted to build a 555 circuit. It had troubles so I added a couple transistors, 2N3904 and 2N3906 and set them up as a buffer. The buffer is capable of firing the IGBT, which for some reason the 555 wouldn't. I don't know why it wouldn't have when it should have. But I have 100% control over the light bulb. I'm assuming it will likewise control the motor.

The test bench proves out a working unit when controlling a light bulb. Next test would be to control the actual fan itself. That is yet to come. As I said, this project is slow to happen, so don't look for a whole lot of updates on this. Nevertheless, this is what I built and (aside from substituting a light bulb for the motor) it works.

555 Blower Speed Control.png
 
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