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Ideally it would work with any load resistance as long as the supply voltage does not drop below the voltage required to ensure proper operation of the regulator. I do expect the output performance to change slightly over that load range. The difficult part of this design is that I need a...
I've had a chance to get back to this design and I tool FvM's advice and pass the total current of the circuit through the shunt resistor. I now have a design that seems to work fairly well except for some ringing in the leading edge of the output pulse. The previous solution for damping the...
The 680 ohm resistor is not a shunt resistor that is part of the design, it is the I/V conversion load resistor which will be outside the loop circuit and is not something I cannot control. It is only in the simulation because it represents the worst case real world load that the circuit is...
Yes. I do want a reasonably accurate (<= 5%) 4-20mA output waveform. That's why I used a voltage reference instead of a regulator. I'm guessing that is why you suggested putting the shunt resistor in line with the current loop so the total current used by the circuit is included in the...
They are different from the defaults. However, clicking the "Reset to Default Values" doesn't seem to make any difference. If your settings are different, please let me know and I will change mine so they are the same. I would feel better if we got the same results.
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Here it is. One thing I missed is that the loop current is no longer correct. The loop current now swings from ~5.6ma to ~19.9mA. I'm guessing there is a voltage drop caused by the resistors used to minimize the overshoot which is causing the loop current control voltage issue. I can...
Thanks for the help. I don't know why I didn't think of the diode. The only issue I have with the changes you made is the 5V regulator. I need the circuit to operate somewhere in the 4-4.5V range so a 5V regulator isn't going to work. I'll have to use a lower voltage or adjustable regulator...
That's why I embedded the subcircuit model for the transistor. All of the other models were stock LTSpice assemblies. That's why I didn't include them. I update my LTSpice regularly so maybe the LT models I used are new.
I'm attempting to design a 4-20mA loop powered pulse output circuit for a sensor. If you look at sample circuit1, I can easily produce a clean signal across the load resistor using a typical current shunt resistor, load transistor, and an op-amp to control the current through the transistor...
Which resistance makes the most sense to control, in series with the emitter resistor or in parallel with the collector resistor? What are the advantages and disadvantages of one over the other? Do you have a link to an example so that I can understand how this all fits together? The only...
How would you implement gain control in a simple transistor oscillator circuit? I'm familiar with AGC using op-amps but I'm not seeing how it could implemented in my sample circuit. I may actually need it. I optimized my circuit to yield a pretty clean oscillator signal. However, any changes...
Would the non-linear element need to be in the feedback path and if so where? If it all it would take is a diode to clean up this distortion, that would be ideal.
I'm assuming the 220 ohm resistor is to prevent the collector of the transistor from seeing an AC short across the output capacitor (5.6nF) that is tied to the supply return.
I will have to error on the side of too much gain because this circuit has to work over temperature and tolerate the differences in transistor operating specs. Operating on the razors edge is always dangerous. I like to avoid it whenever I can.
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