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Voltage curves on PC (LM413D)

2017-07-07 21:22  
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The circuit uses a programmablecurrentsource to force increasing discretecurrentvalues and samples thevoltageat the IOUTterminal at each step. A classic curve tracer continuously sweeps avoltagewhile measuring the sourcedcurrent. The possible operations are a singlevoltagemeasurement, a single forced-currentoutput, or a sweep ofcurrentsteps lasting 2.8 msec each and avoltagemeasurement at each step.Trace voltage current curves Voltage curves on PCThe components in Figure 1 provide operation as low as 3V and low power consumption (low quiescentcurrent). The supervisory circuit, IC1, monitors thevoltagefrom the LPT1 port. If you press momentary switch SW1, theoutputcurrentresets to 1 μA. IC2 through IC5, Q1, Q2, and associated resistors R1 through R9 form acurrent-outputD/A converter. Servoamplifier IC3 sets Q1 ‘s collectorcurrent. For the highestcurrent(1 mA), all the resistors connect in parallel (2.048V/2.16 kΩ).Shift register IC4 and open-drain inverter IC5 select which of the
resistors to connect via program control. IC5′s on-resistance is lower
than 40Ω. IC6 and IC7 performvoltagemeasurements (the ADC block). The serialoutput
of IC6, D0, connects to the parallel port at S6. IC6′s clock input
provides timing control. To be safe, operate this curve tracer with
unpowered components.The macros in the downloadable listing contain the basic interface features for changing thecurrent-outputvalues and measuring thevoltageinput. Also, software-calibration coefficients within the code minimizevoltage-measurement gain and offset errors. The user-form references these spreadsheet values.?