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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Hello, i have project that need to have two picomotor controllers. Basically what that is is capacitor, where slope speed on rising/falling edge dictates step direction Here is how it looks like (amplitude is around 130V, and power consumption at maximum 2kHz step speed is around 8W) Ideally i want to make circuit with two logic signal, step and direction, and toggling step i get high speed slope on rising or falling edge. But because i am not that smart, i think i will use MCU with DAC, that will generate 0-1V signal that is needed to turn motor one step , and use LTC6090 to boost DAC output to 130Vpeak (140V max on this op-amp). But i need more current than LTC6090 can provide, and i don't know much about analog amplifiers, could i use push-pull emitter follower? I found circuit like this, but it's for dual power supply, i only have 0-130V System must be compact, no to-247, only SMD parts
Or maybe some one knows better way to do what i want to do ?
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Not sure about pico-motor brand drive tolerances, but it does look like a rather crude ramp drive.
I'd try a 130v regulated source, and use a switched divider to float the ground given the low power dissipation. Thus, the piezoelectric element gets roughly the same ramp generated across the leads and each step can be fine tuned to match element characteristics.
In this case 6 outputs may generate the waveform for Clockwise: 10v (0.05ms), 20v(0.05ms), 80v(0.02ms), 100v(0.03ms), 110v(0.06ms), and 115v(0.10ms).
I'd wager the motor operates reliably under 4 output states...
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
No to 247? Fair enough, many of the things that used only to be available in that are also available in SMD like DPAK
If the motors are high capacitance input and fairly constant, I'd be inclined to ditch all of the low voltage control stuff, and just go straight to logically switched current sources driving the motors directly. Use a high current source for the fast edges, and a low current source for the ramped edges. There are all sorts of ways to make switchable, controlled level current sources. Simply using a FET and driving its gate to a Vgs may be a bit too crude (or may be OK, try the simple stuff first), servoing current in a source resistor would certainly be more accurate. A bipolar current source with 1v across an emitter resistor, feeding into a FET cascode to get the output voltage would be yet another way to do it.
I'm kind of assuming that the kink in the ramp at 100v is more an artifact of how they were doing it, rather than a vital part of the motor direction choice mechanism, so a choice of fast and slow would be all that's required. Using the controllable current source I've drawn, logic could switch the opamp +ve input to one of several voltages, using a DAC as crude as a resistor to ground, and a couple of different value resistors to logic outputs from your controller. That's the easier groundy side. You would need to use a PFET on the +ve rail, and some way of getting the signal up there, perhaps a second current source on the ground simply driving a resistor to +ve rail. Too many options, so little lunchtime.
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Picomotor driver
