Would like some advice about my motor speed control circuit.

[Eric357]

Hello, So I'm am looking for some pointers on my motor speed control circuit that I have put together. I am using a 556 timer IC, but only one side. Any questions just ask. Thanks in advance.

 

[Minder]

Generally a Mosfet is used now to drive the motor.
M.

 

[Eric357]

What is the difference with the mosfet?

 

[duke37]

A npn transistor will need up to 1V to pass the current required, this means that several watts will be dissipated.
A mosfet can be turned on to give a very low resistance so that the dissipation is very low and I doubt if you will need a heat sink. You have 12V which is plenty to turn the fet fully on.

 

[Eric357]

Ok, I have a IRF510, would it work? The motor that I am using should only draw 1.5A @12v. But with the setup now the motor draws 2.1A (roughly)@11v. Here are the motor specs and P/N.

 

[Alec_t]

I have a IRF510, would it work?

Should be fine.

 

[Eric357]

Ok, thanks, gonna give it a try and see what happens. Any suggestions for a use of the other part of the 556 IC?

 

[Minder]

The 555 is only 8 pin.
The IRF520 has half the on resistance if you haven't picked it up yet.
M.

 

[Eric357]

Ok, thank you, but I don't have one, will have to check how much difference between the IRF510 & the IRF520.

 

[Eric357]

Ok, so I replaced the TIP31 with the IRF510 and the 33ohm resistor with a 220ohm resistor to the gate of the IRF510. Was impressed at how much better the circuit is working. Would use a 555 timer but only have a cosmos timer and haven't quite figured out how to make it work.

 

[duke37]

A cmos 555 will use little power and will be able to drive a fet which needs negligible gate current.

 

[Bluejets]

Is the 220R really necessary? Any Gate R for that matter.
Normally I'd just put maybe a 1K to ground.

 

[Eric357]

Ok, will have to try the cosmos timer. As for the 220R at the gate of the IRF510 is in place to keep the mosfet safe. I can't really afford to damage any of my parts. Bluejets, you mentioned putting a 1kR to ground, but from where?

 

[duke37]

Gate resistor.
I have never used a gate resistor and had no trouble. I understand that the purpose is the same as the reason for a grid stopper. The fet can act as an oscillator with the gate capacitance as part of the oscillating circuit and the resistor will damp this.
There will be no current into the fet proper but the gate capacitance needs to be charged and discharged. Obviously, the higher the frequency, the more current is required.

 

[Eric357]

Well had no luck with the cosmos timer, I think it is a bad IC, will have to get another one. Anyway I have one more Regular 555 timer IC and two 556 timer IC's left. I am using a 556 timer IC at the moment and have the extra timer on the IC that I would like to use as a voltage multiplier to run my motor at 18V but still be able to control the speed of my motor. Is it even possible? Thanks in advance for the help and input. I have no real knowledge about electronic's but I am learning by doing, and people like y'all help me be able to DO. Thank you

 

[AnalogKid]

As for the 220R at the gate of the IRF510 is in place to keep the mosfet safe.

A MOSFET is fundamentally different from a bipolar transistor in many ways. One of them is that it does not need external current limiting at its gate to prevent overcurrent damage. A series gate resistor can reduce high frequency noise generation in some switching power supply circuits, but does nothing to "keep the MOSFET safe." Since you are driving the gate with a totem pole output stage (the gate never is floating), you can eliminate the gate series resistor.

ak