| Electronics > Projects, Designs, and Technical Stuff |
| Need help with bi directional constant current source (±100mA) |
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| iMo:
--- Quote from: Hero999 on November 17, 2018, 10:06:34 pm --- --- Quote from: imo on November 17, 2018, 10:30:37 am ---This gives you nice swing (here aprox 45Vpp) on the output. The Load is L1=3.5H with R6=5ohm in series (no idea what is the Resistance of your actuator). Current +/-102.4mA into the Load based on input (here 2.048Vpp sine w/ DC offset +1.024V). Not easy to simulate, however.. Mind it is a simulation only.. Needs some elaboration with R values and final components of choice.. You may add decoupling, output protection diodes, snubbers, etc. (you mess with inductive load) :) --- End quote --- That circuit doesn't give a voltage offset of 1.024V, but a current offset of 102.4mA. --- End quote --- Nope, it is not about an output offset, but DC offset of the input signal generator used in my simulation: --- Quote ---Current +/-102.4mA into the Load based on input (here 2.048Vpp sine w/ DC offset +1.024V). --- End quote --- The OP has got 2 sources at two inputs: 1. a constant +1.024V DC, and 2. the input from a DAC -> 0..+2.048V (=1.024 + 1.024*sin(x), in my simulation). Therefore my simulation follows his setup.. Of course, the simulation/implementation needs some tweaking, as I wrote above. The important point there is the working principle - the transfer function would be (based on my schematics): --- Quote ---R1/R3 = R5/R4 Iout = (Vs1-V1)/R8 * R5/R4 --- End quote --- or something like that :) |
| Zero999:
--- Quote from: duak on November 18, 2018, 03:24:28 am ---Hero, I'm not able to simulate yours (or anyone's) circuits. May I have you run some simulations on your circuits first with a square wave input and then secondly a repeating plus, zero, minus, zero (tri-level) waveform? The load voltage waveforms should be interesting, especially for the non-bridge designs. Thx & cheers, --- End quote --- What software did you use? A square wave, with a decent rise/fall time, will always cause clipping with an inductive load because a very high voltage will be required to achieve such a high di/dt. --- Quote from: imo on November 18, 2018, 08:32:40 am --- --- Quote from: Hero999 on November 17, 2018, 10:06:34 pm --- --- Quote from: imo on November 17, 2018, 10:30:37 am ---This gives you nice swing (here aprox 45Vpp) on the output. The Load is L1=3.5H with R6=5ohm in series (no idea what is the Resistance of your actuator). Current +/-102.4mA into the Load based on input (here 2.048Vpp sine w/ DC offset +1.024V). Not easy to simulate, however.. Mind it is a simulation only.. Needs some elaboration with R values and final components of choice.. You may add decoupling, output protection diodes, snubbers, etc. (you mess with inductive load) :) --- End quote --- That circuit doesn't give a voltage offset of 1.024V, but a current offset of 102.4mA. --- End quote --- Nope, it is not about an output offset, but DC offset of the input signal generator used in my simulation: --- Quote ---Current +/-102.4mA into the Load based on input (here 2.048Vpp sine w/ DC offset +1.024V). --- End quote --- The OP has got 2 sources at two inputs: 1. a constant 1.024V DC, and 2. the input from a DAC - 0..2.048V (=1.024 + 2.048*sin(x)). Therefore my simulation follows his setup.. --- End quote --- Oh I see what you mean, but the input is differential, so it really doesn't matter. Whether the negative input is set to 0V and the input swings from -1.024 to +1.024, or the negative input is set to +1.024V and the input swings from 0V to 2.048V, is immaterial. The output voltage will be the same and fortunately the DC bias voltages on the op-amp inputs will be within the common mode range. I'm surprised you missed the error I made when simulating your circuit: I set the input voltage too high. I think the signal generator on your circuit shows thevoltage swing, but LTSpice uses the peak voltage, so I set it to double what it should be, causing clipping. I did realise after I uploaded the attachment, but decided not to redo it, in the hope you'd notice. |
| iMo:
Fixed above: --- Quote ---The OP has got 2 sources at two inputs: 1. a constant +1.024V DC, and 2. the input from a DAC -> 0..+2.048V (=1.024 + 1.024*sin(x), in my simulation). Therefore my simulation follows his setup.. --- End quote --- OP - original poster, opamp - a device :) |
| iMo:
35y back I messed with a 5 pins chip called TDA2030 - a 14W/36V audio amplifier, basically a power opamp.. Here is the datasheet, pretty obsolete today, but may be there is something newer available today.. |
| iMo:
--- Quote from: duak on November 18, 2018, 03:24:28 am ---I'm not able to simulate yours (or anyone's) circuits. --- End quote --- I've just reinstalled my LTSpice to the latest and the Hero's .asc (double click on it) simulates.. |
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