Very neat! Please show us the complementary circuit, using a PNP mosfet. Then, we would be able to configure an H Bridge Driver for Stepper Motors. That should have a great amount of interest.
The best way would be just to add the p-channel MOSFET on the top-side of what is already there. Then you have a half H-bridge. Easy peasy. Just one extra part. TBH I have only used H-bridges to drive BDC motors for direction control. For steppers I've always used uni-polar motors to make the drive circuitry (and code) a lot simpler. (I'm lazy..)
The secret it to switch the MOSFET as quickly and fully as you can. Thant's what the adjustment was all about. You need to have it fully on or fully off as much as you can and avoid Vgs anywhere near the threshold voltage.
I was calculating the proper value for the collector resistor for the opto-isolator transistor. You want it low enough to fully turn on the MOSFET quickly enough and hard enough to provide as close as possible to full "on" time, quickly enough to limit dissipation in the MOSFET and also limit the current through the collector of the opto-isolator transistor so as not to cause it any damage. Hope that explains it!
I wonder if leaving the solder mask off of the thermal radiating area of copper noticeably improves the thermal radiation. That would make an interesting experiment. Got some sandpaper?
I'm not sure it would, but I don't think the improvement/impairment would substantial .. either way. Here's why. First, the solder mask is very, very thin so it's not much of an insulator. Second, the red color of the solder mask would make a better radiator (black and blue would be even better) than the shiny tinned copper. So, in essence, one will tend to cancel the other out. Maybe worth a try, but I'd probably make a specific set of boards with and without solder mask over the copper pours and a circuit designed to make a controlled amount of dissipation. I'll ad it to my list of possible future projects. More of a physics thing than electronics but intriguing for that reason alone.
@@uni-byte, I think of electronics as the aspect of physics that it is, and I love physics. As a kid I grew up playing with magnets, magnifying lenses, rubber bands, pulleys and string, rockets, candles, whatever did stuff. RF was my holy grail. It was magic. I traded my bicycle for a 2-transistor radio when I was about 10. I figured I got the best of the deal.
Awesome video! I'm going to explore the alternative pulsing scheme for an application where i use a couple of those power wheels modules (DC motor + nylon gearbox) to position an arm angle and rotate a base which i spray paint items with. i need slow speed / good torque. i used a mechanical relay oscillator to achieve fixed high torque pulses , but had no way to control speed . this will be a better control. one question - do you use a fly back shottky diode here? Also is it possible to modify to have the motor contacts shorted during off time in order to kill any momentum thus providing even more "servo-like" control over the motor in ultra-low RPM application ? (basically kind of simulating a servo with a brushed DC motor)
There are two diodes in use in tis video. One is in the MOSFET itself and I have another across the terminals of the motor. I had the 2nd diode there for another project that had long wires supplying the motor and did not want the back EMF traveling all the way to the controller and acting like an antenna. For the 2nd question, for the most part that function is fulfilled by the diodes between on pulses when the motor is being driven. To add a brake function when the motor is stopped you would need a separate circuit that placed a MOSFET or transistor across the motor to short it out and make it difficult to turn. You would have to ensure it was not activated while the motor was being powered. That said, the back-EMF diode does a great job of putting on the brakes all by itself.
@@uni-byte this is great , thanks for the reply. A brake in either motor direction is important so i'm going to play around but definitely will employ your 817 driver circuit . i can live with coding in long/safe dead times as it's only for brief operation at very low freq. That "minimum pulse length" to just get a little movement of the motor is the key concept you've taught me. I'll probably crank the voltage up high to keep that pulse length shortest. ie 12 v motor fed with ~19v laptop brick.
Fascinating demo, never seen pulse position before. This is something I will remember .....cheers !!
Cheers Andymouse!
Very neat! Please show us the complementary circuit, using a PNP mosfet. Then, we would be able to configure an H Bridge Driver for Stepper Motors. That should have a great amount of interest.
The best way would be just to add the p-channel MOSFET on the top-side of what is already there. Then you have a half H-bridge. Easy peasy. Just one extra part. TBH I have only used H-bridges to drive BDC motors for direction control. For steppers I've always used uni-polar motors to make the drive circuitry (and code) a lot simpler. (I'm lazy..)
Nice module! Good explanation.
Many thanks!
I had never heard of pulse position modulation before.
So it’s like variable frequency drive.
Yes it is. And the sound it makes is far more interesting (sci-fi like) than plain old PWM!
It is surprising that mosfet remains that cool with so little heat sinking.
The secret it to switch the MOSFET as quickly and fully as you can. Thant's what the adjustment was all about. You need to have it fully on or fully off as much as you can and avoid Vgs anywhere near the threshold voltage.
Interesting video. At 7:20 I didn't understand your method how to calculate the Rds(on).
I was calculating the proper value for the collector resistor for the opto-isolator transistor. You want it low enough to fully turn on the MOSFET quickly enough and hard enough to provide as close as possible to full "on" time, quickly enough to limit dissipation in the MOSFET and also limit the current through the collector of the opto-isolator transistor so as not to cause it any damage. Hope that explains it!
Thanks for clarification.
I wonder if leaving the solder mask off of the thermal radiating area of copper noticeably improves the thermal radiation. That would make an interesting experiment. Got some sandpaper?
I'm not sure it would, but I don't think the improvement/impairment would substantial .. either way. Here's why. First, the solder mask is very, very thin so it's not much of an insulator. Second, the red color of the solder mask would make a better radiator (black and blue would be even better) than the shiny tinned copper. So, in essence, one will tend to cancel the other out. Maybe worth a try, but I'd probably make a specific set of boards with and without solder mask over the copper pours and a circuit designed to make a controlled amount of dissipation. I'll ad it to my list of possible future projects. More of a physics thing than electronics but intriguing for that reason alone.
@@uni-byte, I think of electronics as the aspect of physics that it is, and I love physics. As a kid I grew up playing with magnets, magnifying lenses, rubber bands, pulleys and string, rockets, candles, whatever did stuff. RF was my holy grail. It was magic. I traded my bicycle for a 2-transistor radio when I was about 10. I figured I got the best of the deal.
@@johnwest7993 Yeah, physics is the root science. That's what I my primary degree in.
Awesome video! I'm going to explore the alternative pulsing scheme for an application where i use a couple of those power wheels modules (DC motor + nylon gearbox) to position an arm angle and rotate a base which i spray paint items with. i need slow speed / good torque. i used a mechanical relay oscillator to achieve fixed high torque pulses , but had no way to control speed . this will be a better control.
one question - do you use a fly back shottky diode here? Also is it possible to modify to have the motor contacts shorted during off time in order to kill any momentum thus providing even more "servo-like" control over the motor in ultra-low RPM application ? (basically kind of simulating a servo with a brushed DC motor)
There are two diodes in use in tis video. One is in the MOSFET itself and I have another across the terminals of the motor. I had the 2nd diode there for another project that had long wires supplying the motor and did not want the back EMF traveling all the way to the controller and acting like an antenna. For the 2nd question, for the most part that function is fulfilled by the diodes between on pulses when the motor is being driven. To add a brake function when the motor is stopped you would need a separate circuit that placed a MOSFET or transistor across the motor to short it out and make it difficult to turn. You would have to ensure it was not activated while the motor was being powered. That said, the back-EMF diode does a great job of putting on the brakes all by itself.
@@uni-byte this is great , thanks for the reply. A brake in either motor direction is important so i'm going to play around but definitely will employ your 817 driver circuit . i can live with coding in long/safe dead times as it's only for brief operation at very low freq. That "minimum pulse length" to just get a little movement of the motor is the key concept you've taught me. I'll probably crank the voltage up high to keep that pulse length shortest. ie 12 v motor fed with ~19v laptop brick.
@@GannDolph Glad I could help. Let us know how it turns out!