Hey everyone, first post here. I could use some help. I don't have much EE experience and have to build a Motor Controller.

I'm trying to use this circuit with the following changes. 5K Pot, 5 V supply, C1 = .22 uF, and a 36 V motor. I am not sure if the changes I made will allow the circuit to work. I am using a TLC555CP IC and a CSD19506KCS mosfet. If anyone can recommend a good circuit building softwware or place to look to find formulas for these things would be a great help as well.

 

That is going be too low for the pot I think.
I have used a simple one here
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
http://www.talkingelectronics.com/te_interactive_index.html

I found that 5khz freq was good for small motor control.
Also place a high speed BEMF diode across the motor.
Max.

 

Thanks for the reply. I already have that IC and Mosfet so I would like to use them. If I drop to a .022 uF capacitor that should bring me up to ~7 kHz. Other than it looks good? For R2 that should be selected to Vsupply/R2 is the input amperage of the motor correct?

 

No the current will depend on the width of the PWM pulse, load and rpm of the motor.
I see what you are getting at. At 5v-15v 10k is not going to be passing any appreciable current.
Max.

 

So how would I select R2? Is it necessary?

 

There are a few configurations for 555 PWM as you can see from the links I posted. I happen to use one of the others which works for me.
Most, the output pin 3 is driving the Mosfet.
Max.

 

The gate of the FET can be pulled low easily by the discharge pin of the 555, but due to the gate capacitance it may struggle to be pulled up quickly enough by R2 = 10k. The result could be overheating of the FET. Ideally you should have an active (low resistance) pull-up device instead of R2. As Max says, pin 3 of the 555 (an active pull-up) usually drives the FET gate.

 

It should be noted that somethings are different in the diagram, like the capacitors and the supply voltage to the mosfet. If I switch 3 and 7, it would work better? No other changes? Or just lower the resistance to in R2? And for the pot, it is an issue that the pot doesn't go close to zero ohms at zero position? The pot reads 360 ohms at zero and I'm worried that it will continue to try to turn the motor.

 

No other changes?

The FET you have is not a logic-level type, so will probably need about 10V for Vgs to turn the FET on fully; otherwise it could overheat. The 555 is a CMOS type with pin 3 rated to source about 20mA. For rapid switching of the FET a higher current is preferable, e.g. as provided by a NPN+PNP push-pull driver itself driven by pin 3.