Building a PWM circuit

[Joit]

Bizzy, A Mosfet works usual like a Capacitor, where the Gate is the one Plate. Usual you connect the Gate to the Positive Terminal over a Resistor to get a Potentialdifferent. But with the 555 Timer you get allready a Potential, even when you drive it with 9V, because this is the Voltage at the Timer Pin3. I assume that the Resistance in the Motor will lower your Inputpulse from 12V to your 9V Timer Voltage, and therefor you dont have anymore a Different at the Potential.
But i would still put a Potentiometer between Timer and the Gate, you may can manage it to lower the Input without big losses from Torque.

[Bizzy]

Bizzy, A Mosfet works usual like a Capacitor, where the Gate is the one Plate. Usual you connect the Gate to the Positive Terminal over a Resistor to get a Potentialdifferent. But with the 555 Timer you get allready a Potential, even when you drive it with 9V, because this is the Voltage at the Timer Pin3. I assume that the Resistance in the Motor will lower your Inputpulse from 12V to your 9V Timer Voltage, and therefor you dont have anymore a Different at the Potential.
But i would still put a Potentiometer between Timer and the Gate, you may can manage it to lower the Input without big losses from Torque.

Hi Joit
I do have a potentimeter I can use between the 3 Pin and the Gate. Will that affect the timing of the pulse as well? If so that would be much easier than swicth capacitors to do so. But Yes I will try that this weekend.
Thanks
Bizzy

[Joit]

Hi,
It will not affect the Frequency because its a Squarewave what you got at Pin 3.
But the Time how long the Mosfet will be on, and i have found, that the Mosfet eats more Energy with to high Gate current.
When it would be a Triangle Wave at the Gate, you could Control the On Time from the Mosfet also, because its like you cut from the Top down at the Gate Signal. That will change the Duty Cicle, On Time even.
You can see it at this Circuit
Circuit Simulator Applet

And you see there too, that your Frequency varies a little bit, when you change with the Resistor the Duty Cycle.
Below in the Window are 2 Scopes, the left one is Monitoring the Output at Pin3, the right one the Mosfet itself.
You can see it, when you move your Mouse into the Scope window there, and look on the Circuit, which Element get light Blue.
Also you are leading Plus over the Resistor at Pin7 (Dis) into Minus, what may is not the best Solution, because it directly Discharge to Minus. I will try to make another one, where you can adjust the Frequency a bit better.
But my Problem at the 555 Timer is still, that when you change one Resistance, that any Values changes, like changing the Pulsewidth affects the Frequency.
But having different Pots in the Tinker Box is not a bad Idea, even the Wire Potentiometer are more handy because they are more solid when there run more then 2 Watts over it.

[Bizzy]

Hi,
It will not affect the Frequency because its a Squarewave what you got at Pin 3.
But the Time how long the Mosfet will be on, and i have found, that the Mosfet eats more Energy with to high Gate current.
When it would be a Triangle Wave at the Gate, you could Control the On Time from the Mosfet also, because its like you cut from the Top down at the Gate Signal. That will change the Duty Cicle, On Time even.
You can see it at this Circuit
Circuit Simulator Applet

And you see there too, that your Frequency varies a little bit, when you change with the Resistor the Duty Cycle.
Below in the Window are 2 Scopes, the left one is Monitoring the Output at Pin3, the right one the Mosfet itself.
You can see it, when you move your Mouse into the Scope window there, and look on the Circuit, which Element get light Blue.
Also you are leading Plus over the Resistor at Pin7 (Dis) into Minus, what may is not the best Solution, because it directly Discharge to Minus. I will try to make another one, where you can adjust the Frequency a bit better.
But my Problem at the 555 Timer is still, that when you change one Resistance, that any Values changes, like changing the Pulsewidth affects the Frequency.
But having different Pots in the Tinker Box is not a bad Idea, even the Wire Potentiometer are more handy because they are more solid when there run more then 2 Watts over it.

Hi Joit
Last evening I placed a potentometer at the gate of my mosfet and you were right, this willcome in very usefull in fine tuning the power flowing into the motor.

Thanks
Bizzy

[Farmhand]

Hi mbrownn, I recommend using either a SG3525 or SG3524 PWM chip, I use a
SG3524 to drive my Tesla coil at over 400 Khz, and I use a SG3525 to drive
my transformer. The SG3525 chip is the better chip but has a slightly lower
max frequency, it can however drive a mosfet directly with no extra driver circuitry,
not even a resistor.
Where as the SG3524 needs a turn off sharpener to work the same.

These can be used for motor control. I can share the circuits I have. But they
are hand drawn. Using schematic drawing programs on the computer gives me
a headache.

There is an application notes PDF for the SG3524 but I can't find it online at
the moment, I can upload it if it can't be found.

It is important to drive a mosfet all the way on as fast as possible and all the
way off as fast as possible to avoid heating the mosfet. I don't think driving a
mosfet with a triangle wave is a good idea. If the mosfet is not turned all the
way on with a 10 volt pulse it's "on" resistance will be higher than it should be.
Same as if it is turned on and off slowly. A very square 10 volt pulse is best,
but it can be a bit more.

SG3525 pdf, SG3525 description, SG3525 datasheets, SG3525 view ::: ALLDATASHEET :::

SG3524 pdf, SG3524 description, SG3524 datasheets, SG3524 view ::: ALLDATASHEET :::

Cheers

[mbrownn]

Hi mbrownn, I recommend using either a SG3525 or SG3524 PWM chip, I use a
SG3524 to drive my Tesla coil at over 400 Khz, and I use a SG3525 to drive
my transformer. The SG3525 chip is the better chip but has a slightly lower
max frequency, it can however drive a mosfet directly with no extra driver circuitry,
not even a resistor.
Where as the SG3524 needs a turn off sharpener to work the same.

These can be used for motor control. I can share the circuits I have. But they
are hand drawn. Using schematic drawing programs on the computer gives me
a headache.

There is an application notes PDF for the SG3524 but I can't find it online at
the moment, I can upload it if it can't be found.

It is important to drive a mosfet all the way on as fast as possible and all the
way off as fast as possible to avoid heating the mosfet. I don't think driving a
mosfet with a triangle wave is a good idea. If the mosfet is not turned all the
way on with a 10 volt pulse it's "on" resistance will be higher than it should be.
Same as if it is turned on and off slowly. A very square 10 volt pulse is best,
but it can be a bit more.

SG3525 pdf, SG3525 description, SG3525 datasheets, SG3525 view ::: ALLDATASHEET :::

SG3524 pdf, SG3524 description, SG3524 datasheets, SG3524 view ::: ALLDATASHEET :::

Cheers

Thanks Farmhand, I might know a thing or two but not about electronics This all helps

[Joit]

Bizzy here is another simple one, did cost me enough time, lol.
Circuit Simulator Applet
The Duty cycle there is about 50%, i didnt play around with, how to change that now.


You could replace your Potentiometer at the Base from the Mosfet with a Resistor, when you measure the Value at the Potentiometer. My Input Power at a Mosfet was sometimes above 1,5Ah, when i had no resistance there at the Gate. I could bring it back to 0,4-0,2 what was actually enough Power, what he did need to switch.
Well anything fine with a Mosfet, usually you should drive it with 12V at the Base that it switch fast.
But it is like a Car what can make black Stripes on the Street. Good to know, that it can, but its not allways neccesary, so far you dont have a High end application.

[Bizzy]

Bizzy here is another simple one, did cost me enough time, lol.
Circuit Simulator Applet
The Duty cycle there is about 50%, i didnt play around with, how to change that now.


You could replace your Potentiometer at the Base from the Mosfet with a Resistor, when you measure the Value at the Potentiometer. My Input Power at a Mosfet was sometimes above 1,5Ah, when i had no resistance there at the Gate. I could bring it back to 0,4-0,2 what was actually enough Power, what he did need to switch.
Well anything fine with a Mosfet, usually you should drive it with 12V at the Base that it switch fast.
But it is like a Car what can make black Stripes on the Street. Good to know, that it can, but its not allways neccesary, so far you dont have a High end application.

HBi Joit
Ok Now I think I understand it better after looking over your simulation.
After mis reading your previous post I was trying to alter the wrong resistor . But This should help quite a bit.
Thanks
Bizzy

[Joit]

I still hope it does work as the Simulator show it, because i am really not sure about it, lol. I did not trow it together for now. The Capacitor that i did use, i think, is replaceable with a lower Value ie 1 µf, what would change to a higher Frequency. I did only forget to change it.

[Bizzy]

I still hope it does work as the Simulator show it, because i am really not sure about it, lol. I did not trow it together for now. The Capacitor that i did use, i think, is replaceable with a lower Value ie 1 µf, what would change to a higher Frequency. I did only forget to change it.

Hi Joit
Hopefully some night this week I can try it out and I can report back.
I do know that the capictor can be replaced with anouther of higher uf and get a wider wave. However i think I am at the point where I need to also work with the resistors as well.
Thanks again
Bizzy