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| LM723 Precision Logarithmic Scale Current Limitation |
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| iMo:
As a big fan of the LM723 vintage regulator here is a simulation which works, but has not been tested in hw yet. Feel free to test :) It is a "precision current limit" setting with logarithmic scale. It means the potentiometer's dial shows "decades" of max current limits (like 1mA-10mA-100mA-1A-10A on the dial). In below picture you may see the Load currents from 1mA to 10A measured by the log amplifier range from 220mV to 590mV at the comparator's input in pretty linear way. You may see below the simulation. I took my junkbox opamps, you may use better ones, of course. For simplicity the opamps are powered from the "bridge voltage", you may lower the voltage for the real opamps you want to use. Also mind the diode in the log amp has some tempco of -2mV/degC. The wiring requires a "Low-Side shunt" (not a problem I think). The Q2 and R7 simulate the internal LM723 current limiting transistor. The R2 should be connected to the LM723 CL pin (the base of the internal CL transistor). Still, in this version of simulation the current you limit includes the operating current of the LM723 as well (I've been using the internal LM723 Vref as the reference for the current limit comparator). |
| Wolfgang:
Hi, two comments: - You could try to use a temp-compensated log amp circuit - where is your loop compensation when in current mode ? This could be tricky because the loop is now very nonlinear Have fun Wolfgang |
| BravoV:
Subscribed, and thanks. :-+ |
| Rerouter:
Just redrawn to make it easier to read the schematic. |
| iMo:
--- Quote from: Rerouter on January 25, 2019, 10:39:37 am ---Just redrawn to make it easier to read the schematic. --- End quote --- Mind your "PSU" is the bridge/filter voltage (input to 723 reg), and your GND is the output terminal of the PSU. The 723' GND is wired to the GND. @Wolfgang: the dynamic parameters of the circuit have not been tested nor simulated. It waits on an adventurous enough reader to try it out :) |
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