I just realized that I have to use some sort of a flip flop as two inputs will basically be one for pules and the other for direction. I think that will make things easier.
Hi Kal,
It would probably be best at this stage to do a bit of system engineering, as opposed to detailed design, just so I can get a clear idea of your objectives. Could you let me know, at a high level, what you would like the system to do, and what the application is?.
Just a few details which need to be specified/resolved:
(1) What type of motor will be used. What voltage and maximum current?
(2) In your last schematic you show, NTE2395 as a NMOSFET which is correct, but you show IFRZ44N as a PMOSFET, but it is also an NMOSFET in fact. In view of this, could you let me know what MOSFETs you are planning on using?
(3) Could you let me know what the output of the microcontroller is; presumably the micro will drive the two optocouplers.
Cheers
spec
You're right again.
This is all an exercise in motion control via a PLC. I will be controlling a motor (I will add another motor later) that for now will turn and provide feed back via encoders.. I will control the speed and direction and that's about it, itwill not do anything special nor will it be connected to any load at this time. But I would like the board/drive to be as reliable as possible.
1-Motor is 24VDC- 3Amps
2-The P-Channel MOSFET Iwill be using is IRF9540N
3-The outputs are 24Vdc one for direction so it will be either 0 or 24Vdc and the other will be pulses of a frequency that I have yet to determine.
Cheers
Kal
My pleasure kal- hope the circuit works OKThanks so much spec. I will learn a lot putting it together and looking forward to it.
That is the best way- divide and conquer.You know something spec, as much as I would like the circuit to work I'm excited to learn from it. I've already bee shopping and will be playing with the optos first and to get a handle on how they work and then after the smoke subsides there will be lots of questions
Hi spec, I put together on a bread board the opto section of the schematic and used LEDs on the Opto's output emitter along with the 5k6 resistor to test it out and it passed with flying colors. they worked just as they are illustrated on the schematic.
1-Mosfets: The absolute maximums of gate voltage is just that, maximums but the designed voltage should be determined by Rds On voltage? So for my N-Channel NTE2395 of +-20V maximum has an Rds-On of .028 Ohms @ Vgs of 10V+ and Id of 31Amps (is that amperage correct?). So how did we determine that 12V is best for this circuit?
Does the MOSFET conduct current between drain and source at different voltage levels?
There's a "Note 5" beside the Rds-On rating that states : "Pulse width <= 300<=s; duty cycle 2%.".
I intend to supply pulse in the range 20-60 Khz with 50% duty cycle. What's that going to do to the MOSFET?
2-Resistors: I understand the resistors in the schematic to be of two functions, voltage dividers and current limiters.
There are different resistors at the bases of same transistor type with the same specification. Why would one have a 10K and the other [2K2]
The BC546 has an absolute maximum of 100mA and Hfe of 110-800. I think you used and number of 300 for a typical Hfe
Q33 and Q31 will be turned on at the same time with 24V+ signal and they have a 10K and 5K6 resistors respectively. The moment both transistors are turned on the resistors will have a current path to ground through Base-Emitter which will form a parallel circuit for the resistors with effective resistance being 3590Ohms @ 24V+ there will be a 6.6mA the base. 6.6x300= 2Amps. BUT the 270Ohm resistor will limit that collector current to a reasonable 18mA. How much current will be flowing through the Base-Emitter of the same transistor, the same 6.6mA, 2A or 18mA?
Is any of that correct or am I just hallucinating
I also wired the MOSFET part and as usual used LEDs for now to test it out and wasn't quite sure why the addition of the transistors on your second schematic why [not] connect the opto section to the first schematic or is there an advantage to second?
**broken link removed**Hi kal,
(4) U1 and U2 emitters, with correction of (1) above, now connect to 0V via 5K6 resistors. This means that CLOCK and ACLOCK output voltage levels are indeterminate:
(4.1) With a worst case current transfer ratio 4N25, the emitter current could be as low as 200uA, so CLOCK and ACLOCK could be as low as 200uA * 5K6 Ohms = 1.12V
(4'2) From the data sheet, a fantastically good 4N25, would have a potential emitter current of infinity (nonsense of course). The emitter current would be limited to 24V/5K6 Ohms= 4.29mA and the VCE of the ORT will be 0V. In this case CLOCK and ACLOCK outputs will be 24V. Also, the ORT will be operating outside the conditions specified by the data sheet.
HI spec,
Thanks for your great feedback. The circuit is not complete as I was only playing with the PLC input to change one input to be directional but I will be using the rest of your circuit as you designed it so I didn't add it in my schematic. Just being lazy. Basically the output half the optos is going to be exactly as in your schematic so the the labels Clock and Anti-clock will connect to R23 and R24 on your schematic.
Some software provides an already built in "motion control device" that includes a direction output in addition to the pulse output and I pass parameters to that device to control the output. Another motion control device will put out only a pulse and I have to write my own code to control the output direction. I would like to work with both types to take advantage of the built in code.
Cheers
Kal
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