Mosfet & Motors

[Bizzy]

Mosfet Drivers

Good afternoon
Could anyone also explain what a mosfet driver circuit is and why it works?
thanks
Bizzy

[Bizzy]

PWM mosfet motor controller

Good morning,
I have been working with mosfets and 555 circuits with much sucess.
However previously I been running the motors on the same voltage as the 555 circuit. But lately I have been trying to run larger voltage motors using a 555 circuit and mosfets, unfortunately in several cases my mosfets over heat and burn out.
Attached are some of the circuits I have tried and I was wondering if someone could tell me what I am doing wrong or perhaps recommend a beeter circuit to run a 12 volt motor from a 5 volt 555 circuit.
Much thanks
Bizzy

[citfta]

Hi Bizzy,

Go back to post number 11 in this thread. There I posted a motor control using a mosfet. The input can be your output from the 555. Instead of the FOD3120 I would use the FOD3180 as it has a lower voltage lockout voltage. The lockout voltage is a circuit in the chip that keeps the output turned off if the supply voltage gets too low. The purpose of that circuit is to prevent the mosfet from turning on part of the way caused by too low of a voltage to the gate. I believe from looking at your drawings that is your problem. You are not turning on the mosfet all the way and that is causing your overheating problem.

The mosfet gate driver chip also turns on and off the mosfet faster which also helps to keep the mosfet from overheating. A mosfet or any transistor will heat up if it is only turned on part of the way and you try to control a large load with it. You want the mosfet all the way on or all the way off.

Carroll

[Bizzy]

Hi Bizzy,

Go back to post number 11 in this thread. There I posted a motor control using a mosfet. The input can be your output from the 555. Instead of the FOD3120 I would use the FOD3180 as it has a lower voltage lockout voltage. The lockout voltage is a circuit in the chip that keeps the output turned off if the supply voltage gets too low. The purpose of that circuit is to prevent the mosfet from turning on part of the way caused by too low of a voltage to the gate. I believe from looking at your drawings that is your problem. You are not turning on the mosfet all the way and that is causing your overheating problem.

The mosfet gate driver chip also turns on and off the mosfet faster which also helps to keep the mosfet from overheating. A mosfet or any transistor will heat up if it is only turned on part of the way and you try to control a large load with it. You want the mosfet all the way on or all the way off.

Carroll

Hi Caroll
Thank you once again for your advise
Bizzy

[Bizzy]

Hi Bizzy,

Go back to post number 11 in this thread. There I posted a motor control using a mosfet. The input can be your output from the 555. Instead of the FOD3120 I would use the FOD3180 as it has a lower voltage lockout voltage. The lockout voltage is a circuit in the chip that keeps the output turned off if the supply voltage gets too low. The purpose of that circuit is to prevent the mosfet from turning on part of the way caused by too low of a voltage to the gate. I believe from looking at your drawings that is your problem. You are not turning on the mosfet all the way and that is causing your overheating problem.

The mosfet gate driver chip also turns on and off the mosfet faster which also helps to keep the mosfet from overheating. A mosfet or any transistor will heat up if it is only turned on part of the way and you try to control a large load with it. You want the mosfet all the way on or all the way off.

Carroll

Hi Caroll
Now that I have been working with 555 chips I can ask intellegent questions(although I freely admit I am NO expert like you and Bit )
In looking intellengently at your circuit I have a few questions. The drawing on the chip left the numbers a little off is the 1k resistor on the 2 pin? and the ground on the 3 pin?
I am using a small battery for running the 555 chip and a larger 12 volt battery running the motor so my other question is should the ground of both batteries be connected? If so then if I understand this correctly the 2 pin with the 1k resistor would go to the positive of the smaller battery and the 12-48 volts+ would go to the positive of the 12 volt battery with both negitives connected for power return?
Does that sound right to you?
thanks again
Bizzy

[citfta]

Hi Bizzy,

The output of your 555 goes to pin 2 through the 1 k resistor. The ground on pin 3 is the return back to the same negative as the negative of the 555. The negatives of the 555 supply and the 12 - 48 volts or so do not need to be tied together. That is what makes this a nice way to control things, you can keep your supplies isolated from each other.

I'm glad you are learning about the 555 chip. It is a really neat chip that can be used to do a lot of different things. There is also a version of the chip that will run on up to 25 volts I think. I would have to look it up but I am sure it is over 20 volts. I guess you are using the cmos version because it is the regular version that will handle the higher voltage if I remember correctly.

It is a shame that so many of the people on this forum won't take the time to try and learn more about how to do things the right way. As you know there are some on here that just want to rant about how much more they know than anyone else when it is obvious they don't really know anything. I have learned so much from some of the real gurus on here and have tried to share some of what I have learned but there are only a handful of you that seem to really want to learn. Oh well enough of that I guess.

Later, Carroll

[Bizzy]

Hi Bizzy,

The output of your 555 goes to pin 2 through the 1 k resistor. The ground on pin 3 is the return back to the same negative as the negative of the 555. The negatives of the 555 supply and the 12 - 48 volts or so do not need to be tied together. That is what makes this a nice way to control things, you can keep your supplies isolated from each other.

I'm glad you are learning about the 555 chip. It is a really neat chip that can be used to do a lot of different things. There is also a version of the chip that will run on up to 25 volts I think. I would have to look it up but I am sure it is over 20 volts. I guess you are using the cmos version because it is the regular version that will handle the higher voltage if I remember correctly.

It is a shame that so many of the people on this forum won't take the time to try and learn more about how to do things the right way. As you know there are some on here that just want to rant about how much more they know than anyone else when it is obvious they don't really know anything. I have learned so much from some of the real gurus on here and have tried to share some of what I have learned but there are only a handful of you that seem to really want to learn. Oh well enough of that I guess.

Later, Carroll

Hi Caroll
Forigive me for repeating becuase I just want to make sure I have it correctly
The smaller battery positive is connected to the 1k resistor and then the 2 pin whereas the 3 pin gets connected to the negative of the same smaller battery to where the 2 pin s connected to its positive? and no mutual grounding between the larger and smaller bateeries?
That would isolate the two batteries from each other and allow the higher voltage to remain in the motor circuit. Wow that will be great. AND EXACTLY WHAT I AM LOOKING FOR

As far as the rest of your comment... I am old enough to know that I dont know everything and not too proud to admit it and learn.
Let me know if I am on the right track.


Thanks again
Bizzy

[citfta]

Hi Bizzy,

Pin 2 is the signal input of the gate driver chip. This chip does not need a power connection. Pin 2 and the 1 k resistor get connected to the output of the 555 chip. I believe that is pin 3 of the 555 chip. The smaller battery positive only gets connected to the supply pin of the 555 chip. If you connected pin 2 of the gate driver chip to the smaller battery positive then the mosfet would be on all the time because you would have the input to the mosfet gate driver chip on all the time. And yes there is no mutual grounding between the two different supplies. If this is still not clear let me know and I'll try to draw it out for you.

Later, Carroll

[Bizzy]

Hi Bizzy,

Pin 2 is the signal input of the gate driver chip. This chip does not need a power connection. Pin 2 and the 1 k resistor get connected to the output of the 555 chip. I believe that is pin 3 of the 555 chip. The smaller battery positive only gets connected to the supply pin of the 555 chip. If you connected pin 2 of the gate driver chip to the smaller battery positive then the mosfet would be on all the time because you would have the input to the mosfet gate driver chip on all the time. And yes there is no mutual grounding between the two different supplies. If this is still not clear let me know and I'll try to draw it out for you.

Later, Carroll

Hi Caroll
I am still a little fuzzy about where the smaller battery is connected to the chip so if you could send a diagram that would be a great help.
But again with no mutual ground I feel this is the circuit I have been looking for.
Thanks again
Bizzy

[citfta]

Hi Bizzy,

The smaller battery does not get connected to the chip. The only power connection for the chip is from the higher voltage side. This connection is to pin 8 with the protection resistor and zener so it can be run on higher voltages. The 555 output and a common ground for the 555 and the gate driver chip are the only connections on the input side of the chip. I have added the 555 chip to the earlier drawing. Depending on the mosfet you are using you may have to lower the value of the 2.2 k resistor. I would start with a value of 1 k for what you are doing. If you are driving a high current mosfet that value may even need to be as low as 2 ohms. If you have to go that low you will need to make sure the zener is rated for 5 watts. Hope this helps.

Carroll

[Bizzy]

Hi Bizzy,

The smaller battery does not get connected to the chip. The only power connection for the chip is from the higher voltage side. This connection is to pin 8 with the protection resistor and zener so it can be run on higher voltages. The 555 output and a common ground for the 555 and the gate driver chip are the only connections on the input side of the chip. I have added the 555 chip to the earlier drawing. Depending on the mosfet you are using you may have to lower the value of the 2.2 k resistor. I would start with a value of 1 k for what you are doing. If you are driving a high current mosfet that value may even need to be as low as 2 ohms. If you have to go that low you will need to make sure the zener is rated for 5 watts. Hope this helps.

Carroll

Hi caroll
Ok I think I understand better now. I didnt realize the the gate driver chip and the 555 were seperate components. That was my misunderstanding of the schematic. I dont understand it completely yet but atleast I know what direction i need to go in.
I am sure I'll be back with more questions once i get the gate driver chip.
Thanks Again
Bizzy

[Bizzy]

Snubber circuits

Good morning
I want to install an RC snubber circuit to prevent arcing across a switch.
I have read of several versions and am uncertain which is correct so I thought I would ask you folks.
Should the snubber cicuit be in parrallel to the switch or the motor or both?
Or is any one of these ok?
Let me know.
thanks
Bizzy

[yingxuy]

MOSFET driver chip provides faster opening and closing than you can use the resistance. Transistors on a chip, or the ground terminal of the supply-side output pins. Resistance helps to let go of the gate voltage MOSFET, a faster close.

[Bizzy]

Watson Machine

Good morning
Everyone,
I apologize that I have not been on line lately, The stress at my job has increased by 1,000% plus I am trying to get back into the jail (as a CO)

Any way I wanted to let you know I am still working on my Watson machine and think I made a break through in switching that allows me to run a DC motor directly from an alternator without effecting the alternator itself. I hope to post my video soon.

Bizzy