My question came out of surprise that my circuiit was even mentioned at all as it was not being discussed as far as I'm aware. Anyway I designed this circuit for a 24V system and motor loads of around 6A which is also why I used complementary output stages as it led to a very compact design at the time.
Your circuit was listed as an example in the requirement spec at the top of this thread. I just wanted to express concerns over that design in case the design was taken up by someone who didn't completely understand what they were doing.
High-side N channel drive:
Now I stumped by your remark that the just because the charge pump is referenced off the high-side-source voltage (as they are) that it isn't a problem. In stall conditions and also if motor direction is reversed instantly (sink to source) the Nch source's "source" will be at close to 0V or even negative which means that if you are using a high-side drive voltage of 34V in a 24V system then the gate-source will see 34V or more and yet the gate-source will normally breakdown at 20V. So this juncture needs to be protected adequately or else the destruction is sudden and catastrophic.
No, the charge pump is referenced to the source-terminal of the high-side N-Channel MOSFET, not the power source. That way, the gate drive tracks 10V (or whatever the low supply voltage is) above the source of the high-side MOSFET, no matter what happens. So, in a stall, the high-side gate drive is still 10V, even though, it's driven by a charge pump. See the IRS2184 datasheet for the topology I'm talking about.
Your circuit was listed as an example in the requirement spec at the top of this thread. I just wanted to express concerns over that design in case the design was taken up by someone who didn't completely understand what they were doing.
No, the charge pump is referenced to the source-terminal of the high-side N-Channel MOSFET, not the power source. That way, the gate drive tracks 10V (or whatever the low supply voltage is) above the source of the high-side MOSFET, no matter what happens. So, in a stall, the high-side gate drive is still 10V, even though, it's driven by a charge pump. See the IRS2184 datasheet for the topology I'm talking about.
Oh okay, but references are references and not final designs I hope as many factors need to be taken into consideration. Regarding the high-side supply I see what you are saying but wouldn't it need to track the source pin rapidly?
That's why the cap sits right on the source pin directly. It's charged by the bottom-side MOSFET and a diode on the low cycle. If you're driving a stepper, and need holding torque without moving, you'll still be chopping the drive to limit the current, so it'll still get charged plenty often.
I'm familiar with using boot caps when chopper driving steppers but I wasn't thinking of steppers but of driving DC motors which is what the driver was designed for. Bootstrap caps are useless unless you chop the output with enough on/off time to be useful but DC motors often need to run flat out.
Nice find! However the downside of that chip is that it requires a 12 volt supply in addition to the H-bridge power supply. But I must say, it caught my interest. Thanks for sharing.
I'm familiar with using boot caps when chopper driving steppers but I wasn't thinking of steppers but of driving DC motors which is what the driver was designed for. Bootstrap caps are useless unless you chop the output with enough on/off time to be useful but DC motors often need to run flat out.
Looking at the datasheet for the DRV8412, mentioned by ErNa, it also uses bootstrap caps, even though it's designed to run regular brushed motors as well. It looks like it supports running at up to 99% duty cycle, recommending a .1u boot cap for frequencies from 10Khz to 500Khz.
@idbruce, Looks like the L6208 has an internal 10V regulator used to create the supply voltage. In a system where you have multiple drivers, it seems like a waste to have the LDO built into the same chip when you may want a global switching regulator. Since all high-side gate drivers share one bootstrap cap, the gate drivers also need to limit gate current in the cases Peter Jakacki listed:
Regarding high-side n chanel drivers there is one great problem (of many) in that the gate is rather sensitive to fault conditions where the high side nch source appears to be grounded or even worse at a negative potential. With a gate breakdown of around 20 volts this means instant and cataclysmic destruction unless the gate source is properly clamped. Motors are mischievous things.
That results in yet more driver dissipation and a more complex design. So it costs even more than the TI design, despite having lower current handling.
That results in yet more driver dissipation and a more complex design. So it costs even more than the TI design, despite having lower current handling.
Point well taken. Should this controller actually develop, it will be interesting to see the final design. I just wonder how many different voltages and/or power supplys will be required. As mentioned in several of my other posts, dealing with multiple power supplies can be a pain.
I now see the Power Conversion Circuits section requires a 5 VDC switching regulator. I would hopefully assume this will be fed from the same power supply that will go to the motor drivers.
Personally I agree with some of the other posts pertaining to the motor drivers being daughter boards. I think they should just design a couple stepper drivers that can handle several voltages and currents, and which can then be added to the main controller board. In my opinion, the motor drivers are more important than the purpose of the whole project. Compare the stepper driver market to the RepRap market. By tying the motor drivers to a board with a specific purpose, you lose a lot of potential customers, but on the other hand, you may gain a large share of a smaller market.
This is the stepper driver used on my RepRap derived machine: http://www.pololu.com/catalog/product/1182 The controller board connects to 4 of these.
There are details on this page about how it uses them: http://reprap.org/wiki/Sanguinololu In my machines case it's using 12v and 0.4A for the motor drive side (the 0.4A limit is adjustable on the pololu board).
They sells these boards for $12.95 including the pin headers needed to socket them. That goes down to $9.71 if you buy 100 units. Prior to seeing this thread (I skipped the other one because it wasn't clear that it was intended for RepRap like machine control), I had been planning to try and make a Prop based board that was very similar to the Sanguinololu. Although, I was planning to put all the MS1-3 pins on a shift register to allow for software configuring of the step fraction. I think it would only require 12-14 pins to handle 5 of these, assuming step/dir are connected directly, and the rest (enable, reset, sleep, and MSx) are on shift registers. I might still do this when I have some time, and give it to Ken/Jessica to see if they are interested in it for Parallax.
A co-worker of mine is Wayne of Wayne & Layne. He says the design of that controller is quite horrible, that the chip puts more heat down than up, and that the board is not designed with a large thermal pad to move heat around.
Looking further at stepper motors you can buy at Pololu, the largest one is 1200mA, and it says 4V. I suspect that 12V drive with current limiting will allow much faster operation. That does narrow things down a bit. Anyone know if being able to drive bigger steppers would be helpful?
Circuitsoft,
Looking at the pictures, it appears that the A4988 board has the thermal vias called for in the datasheet for the chip. In any case, mine and a great deal many of others have been working fine.
I keep forgetting to also link the RepRap RAMPS electronics stuff that supports 5 drivers: http://reprap.org/wiki/RAMPS1.4 It's setup as a shield for a Arduino Mega.
I have also considered a "shield" for the GG PPM as part of my idea.
I need to source a Prusa Reprap and would love to control it with a Propeller if possible (now or later). No point ordering the Ramps kit if the propeller version is close.
Tubular,
I currently have a RAMPS setup running on my eMaker Huxley (reprap based 3d printer), and am "learning" my way through doing an interface adapter between a Gadget Gangster Prop Platform USB and the RAMPS. Once I have that, I plan to work on code for the Prop that emulates the Repetier firmware that I am currently using on the Arduino Mega 2560 with the RAMPS 1.4. Repetier is a spinoff of the Sprinter firmware. Anyway, It's slow going, but I figured I'd let you know I what I was doing.
Thanks Roy. Good to know what you and others are doing. Until now I haven't followed closely any of the 3d printing in any detail, now suddenly find myself with a budget and need to get up to speed to get some parts in. As usual half of that is understanding the lingo, and tips/traps with the various designs out there.
This is a long term thing for us, though we do have an immediate application that would easily pay for the reprap if it works. I'm not really expecting brilliant results first up. Happy to go with a RAMPS 1.4 controller for now and adopt a propeller version as soon as anyone makes one available. Down the track may also be able to spare some co-operative development effort.
Right now, I'm building a dual H bridge with current monitoring and adjustable hardware chopping to play with characterizing a stepper motor to see if I can have the MCU detect when a step has been missed and current needs to increase. When done, I'll be designing my own RAMPS-like hardware.
I do plan to put an ATX PSU header on it, with an optional boost converter to draw enough off the 5V line to keep 12V steady.
Sounds good Circuitsoft. I think the propeller is a natural fit for CNC style applications, and there's plenty of scope for next generation controllers that can deal with mis-steps, cameras, autocalibrations, and improved HMI. Its going to be a fun ride.
FWIW I have two pcbs...
A Pololu compatible stepper driver pcb using the TSSOP A4982/A4984. If you use the Pololu make sure you get the A4988 version.
I have a carrier pcb for 4 of the above drivers (1.75" sq). It has a 1x14 SIL connector with the connections 5V, Gnd, P0..P11 (not all used) so it will connect easily to a prop pcb, or any other (atmega) easily.
I use a t/h resistor to set the current limit rather than a pot (large holes to make it easy to resolder). This makes it easy to set a known current limit.
In this case, the adjustable chopping is driven by a DUTY-mode counter and R/C filter. I did put a limiter in the design so I don't burn out the motor.
The motor in question is a Sanyo Denki 103H5208-1241 1.6Ω 1.8° NEMA17 motor. The person who gave it to me says it's what he's using in his RepRap, and that the speed limit on his is the speed that the filament hardens at, not how fast the motors can go. On that note, I see no reason to support >12V/4A on any motor drivers.
Comments
No, the charge pump is referenced to the source-terminal of the high-side N-Channel MOSFET, not the power source. That way, the gate drive tracks 10V (or whatever the low supply voltage is) above the source of the high-side MOSFET, no matter what happens. So, in a stall, the high-side gate drive is still 10V, even though, it's driven by a charge pump. See the IRS2184 datasheet for the topology I'm talking about.
Oh okay, but references are references and not final designs I hope
Nice find! However the downside of that chip is that it requires a 12 volt supply in addition to the H-bridge power supply. But I must say, it caught my interest. Thanks for sharing.
Bruce
Please refer to http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002294.pdf
Bruce
Point well taken. Should this controller actually develop, it will be interesting to see the final design. I just wonder how many different voltages and/or power supplys will be required. As mentioned in several of my other posts, dealing with multiple power supplies can be a pain.
I now see the Power Conversion Circuits section requires a 5 VDC switching regulator. I would hopefully assume this will be fed from the same power supply that will go to the motor drivers.
Bruce
@RonP Can you chime in on voltage/current for the motors a RepRap usually uses?
Personally I agree with some of the other posts pertaining to the motor drivers being daughter boards. I think they should just design a couple stepper drivers that can handle several voltages and currents, and which can then be added to the main controller board. In my opinion, the motor drivers are more important than the purpose of the whole project. Compare the stepper driver market to the RepRap market. By tying the motor drivers to a board with a specific purpose, you lose a lot of potential customers, but on the other hand, you may gain a large share of a smaller market.
Bruce
There are details on this page about how it uses them: http://reprap.org/wiki/Sanguinololu In my machines case it's using 12v and 0.4A for the motor drive side (the 0.4A limit is adjustable on the pololu board).
They sells these boards for $12.95 including the pin headers needed to socket them. That goes down to $9.71 if you buy 100 units. Prior to seeing this thread (I skipped the other one because it wasn't clear that it was intended for RepRap like machine control), I had been planning to try and make a Prop based board that was very similar to the Sanguinololu. Although, I was planning to put all the MS1-3 pins on a shift register to allow for software configuring of the step fraction. I think it would only require 12-14 pins to handle 5 of these, assuming step/dir are connected directly, and the rest (enable, reset, sleep, and MSx) are on shift registers. I might still do this when I have some time, and give it to Ken/Jessica to see if they are interested in it for Parallax.
Looking at the pictures, it appears that the A4988 board has the thermal vias called for in the datasheet for the chip. In any case, mine and a great deal many of others have been working fine.
I keep forgetting to also link the RepRap RAMPS electronics stuff that supports 5 drivers: http://reprap.org/wiki/RAMPS1.4 It's setup as a shield for a Arduino Mega.
I have also considered a "shield" for the GG PPM as part of my idea.
I am running the same set up as Roy. Here is a link to the reprap wiki on steppers. Here is the Data sheet to the steppers I am using.
I haven't seen a need for larger than the NEMA 17 steppers in all my reading as far as reprap is concerned.
Ron
Any update on this?
I need to source a Prusa Reprap and would love to control it with a Propeller if possible (now or later). No point ordering the Ramps kit if the propeller version is close.
I currently have a RAMPS setup running on my eMaker Huxley (reprap based 3d printer), and am "learning" my way through doing an interface adapter between a Gadget Gangster Prop Platform USB and the RAMPS. Once I have that, I plan to work on code for the Prop that emulates the Repetier firmware that I am currently using on the Arduino Mega 2560 with the RAMPS 1.4. Repetier is a spinoff of the Sprinter firmware. Anyway, It's slow going, but I figured I'd let you know I what I was doing.
This is a long term thing for us, though we do have an immediate application that would easily pay for the reprap if it works. I'm not really expecting brilliant results first up. Happy to go with a RAMPS 1.4 controller for now and adopt a propeller version as soon as anyone makes one available. Down the track may also be able to spare some co-operative development effort.
I do plan to put an ATX PSU header on it, with an optional boost converter to draw enough off the 5V line to keep 12V steady.
A Pololu compatible stepper driver pcb using the TSSOP A4982/A4984. If you use the Pololu make sure you get the A4988 version.
I have a carrier pcb for 4 of the above drivers (1.75" sq). It has a 1x14 SIL connector with the connections 5V, Gnd, P0..P11 (not all used) so it will connect easily to a prop pcb, or any other (atmega) easily.
I use a t/h resistor to set the current limit rather than a pot (large holes to make it easy to resolder). This makes it easy to set a known current limit.
I have not had the time to assemble these yet.
The motor in question is a Sanyo Denki 103H5208-1241 1.6Ω 1.8° NEMA17 motor. The person who gave it to me says it's what he's using in his RepRap, and that the speed limit on his is the speed that the filament hardens at, not how fast the motors can go. On that note, I see no reason to support >12V/4A on any motor drivers.