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Syscomp Computer Controlled Instruments

CTR-201 Curve Tracer

Syscomp Electronic Design Limited

http:\\www.syscompdesign.com

Revision: 2.1

November 2017

Summary of Contents for CTR-201

Page 1: ...Syscomp Computer Controlled Instruments CTR 201 Curve Tracer Syscomp Electronic Design Limited http www syscompdesign com Revision 2 1 November 2017 ...

Page 2: ...eneral 2 Terminal Measurement 13 3 10 1 2 Terminal Measurement Voltage Mode 13 3 10 2 2 Terminal Measurement Current Mode 14 3 11 Small Signal Transistors 14 3 12 Solar Cells 14 3 13 Lambda Diode Negative Resistance Device 15 3 14 Vacuum Tube 15 4 How It Works 16 5 Calibration 21 6 Installing the Software 23 6 1 Packaged Executable 23 6 2 Source Code 23 6 2 1 Obtaining the Source Code 23 6 2 2 Ins...

Page 3: ...0 N Channel JFET 12 11 2 Terminal Measurement Voltage Mode 13 12 2 Terminal Measurement Current Mode 14 13 2N4401 NPN BJT 15 14 2N4403 PNP BJT 16 15 2N7000 N Channel MOSFET 17 16 Solar Cell 18 17 Lambda Diode 18 18 Lambda Diode 19 19 Vaccum Tube 19 20 Curve Tracer Block Diagram 20 21 Attaching to the Ground Point 21 22 Calibration Panel 22 23 BJT Comparison 28 24 48V Power Enable Disable 29 ii ...

Page 4: ...lts Across an LED it is 2 or 3 volts Figure 1b shows the VI characteristic of a 3 amp silicon power diode The curve tracer can also plot a family of VI Curves for NPN and PNP transistors MOSFETs JFETs and many other semiconductor devices Applications of a curve tracer include the following Education Viewing Device Characteristics A lab exercise to measure device characteristics such as the col lec...

Page 5: ...esign and troubleshooting it s often important to be able the exact behaviour of a given device For example the forward voltage of a silicon diode is often quoted a 0 6 volts A curve tracer shows that the forward voltage of an MR851 diode when conducting 1 amp of current is actually about 1 4 volts This would be important to know when designing a power supply1 2 The CTR 201 Curve Tracer Early exam...

Page 6: ...device under test Then as the current was increased in the device the voltage across the device decreased This was a useful approach to protect the device under test2 However it limited the measurement at the corner values of voltage and current You could measure the device at maximum voltage or current but not both at once The CTR 201 contains no dissipation limiting resistances and the current s...

Page 7: ...device under measurement Here we list the various functions on the control panel of the Curve Tracer These are the functions that apply to all measurements Menu Bar File Save Preset Saves the current control settings Load Preset Loads the previously saved control settings Menu Bar View Trace Smoothing Enable and disable dot connection algorithm that smooths the trace Disable to see the actual meas...

Page 8: ...firmware upgrades on startup Recommended to leave this enabled To upgrade the firmware an internet connection is required of the host computer Device Status Temperature Shows the internal temperature of the instrument USB Voltage Displays the voltage supplied by the USB connection Should be around 5 volts Input Voltage When taking a measurement shows the supply voltage from the AC adaptor Should b...

Page 9: ...ill read the values in these boxes Usually some experimentation is required to get the desired curve Curve Data This section of the control panel logs the measured values as they are completed The Save CSV function see above copies this data to a CSV file Measurement Cursors Figure 3 Cursors A left click in the plot area deposits a measurement point and shows the coordinates of that point A second...

Page 10: ...current source sink is available at the centre Blue terminal For the Diode measurement the software selects sourcing of current from that terminal The left Red terminal acts as a constant voltage source for return for the current 3 4 Zener Diode The zener diode should be measured using the Diode measurement configuration which is current controlled Figure 5 shows the characteristics of a 1N3022 ze...

Page 11: ... a Forward b Reverse Figure 5 1N3022 Zener Diode 8 ...

Page 12: ...rent of 1 ampere the transistor dissipation is 30 watts A small signal transistor might have a maximum power dissipation of 0 5 watts Consequently it s very easy to destroy a transistor by exceeding the power dissipation To prevent this While learning how to operate the curve tracer use a power transistor as the device The 2N3055 is a good choice since it is inexpensive readily available has a lar...

Page 13: ...IP32C and the results of that measurement are shown in figure 7 As mentioned in section 3 5 one must exercise caution not to destroy the PNP device under test by excessive current or power dissipation 3 7 N Channel MOSFET The control settings for an N Channel MOSFET IRF820 and the results of that measurement are shown in figure 8 Notice that the MOSFET drain current is essentially zero when the ga...

Page 14: ...JFET The control panel settings and a typical result are shown in figure 10 For the JFET the value of Idss drain current with zero gate source voltage is often of interest This can be obtain from the VI plot However to eliminate any possible voltage between gate and source it s useful to connect only the source and drain terminals to the curve tracer as in figure 10 The gate terminal is connected ...

Page 15: ... a Control Settings b Result Figure 9 P Channel MOSFET a Control Settings b Result Figure 10 N Channel JFET 12 ...

Page 16: ... series The result is a device with approximately 1 4 volt threshold in one direction and a 2 1 volt threshold in the other direction This test is voltage driven Testing a constant voltage device such as a diode or zener can easily result in a measured current that exceeds the maximum current setting In that case a warning window will pop up Reduce the test voltage and then try the measurement aga...

Page 17: ...ices are packaged in a TO 92 package and are very limited in dissipation These settings and results will be useful in providing a starting point for setting the controls for other small signal devices 3 12 Solar Cells The 2 terminal VI curve control panel for measuring solar cells is shown in figure 16 a on page 18 The solar cell is connected with its positive terminal to the collector red termina...

Page 18: ...s to an ambiguous result A voltage source creates a load line that is vertical and changes its horizontal position This load line can intersect with the VI characteristic at one point only so the result is unambiguous Consequently the device should be driven by a constant voltage source while measuring the current In the CTR 201 that implies connecting it between the collector Red and emitter Blac...

Page 19: ... is not available to the outside world Measurements are performed between the three terminals The base current generator actually consists of two current sources Isource supplies current out the Base terminal Isink accepts current into the Base terminal At any given time only one of these sources is active The compliance of the current source is equal to the full voltage range of measurements abou...

Page 20: ...he Base terminal and the cathode to Collector terminal The base current source forces current through the diode The ammeter in the Collector circuit measures this current4 The voltage across the diode is equal to the base voltage reading minus the collector voltage reading Example PNP Transistor Measurement The PNP transistor is connected to the like named terminals on the curve tracer The emitter...

Page 21: ...a Diode collector emitter voltage moves over the range demanded by the software During the sweep the microprocessor captures the collector emitter voltage and collector current readings and sends them to the host The base current generator then steps to its next base current and the voltage sweep repeats 18 ...

Page 22: ... a Control Settings b Result Figure 18 Lambda Diode Figure 19 Vaccum Tube 19 ...

Page 23: ... to 1A step 200uA Collector Emitter Voltage Drive Vo 3 15V to 42V minimum step 9 5mV Emitter Voltage Measured 0 to 42 volts resolution 11mV Collector Voltage Drive Vo 3 15V to 42V minimum step 9 5mV Collector Current Measured Low Range 100nA to 1mA resolution 15nA 16 bit High Range 100uA to 1A resolution 15uA 16 bit Collector Voltage Measured 0 to 42 volts resolution 11mV r r r r r r r r r r r Fig...

Page 24: ...5 Calibration a Ground Point b Attaching to Ground Figure 21 Attaching to the Ground Point 21 ...

Page 25: ... straight line equation y Mx B The calibration procedure establishes the values of slope M and y offset B It does this by outputting an assumed value eg 10 volts The operator then enters the actual output voltage Doing this twice provides two equations in two unknowns so that the actual values of slope M and y offset B can be determined In general the values of slope will be fairly close to unity ...

Page 26: ...s but cannot take the existing code private Protection against Obsolescence Syscomp employees are subjected to an alien abduction and no longer avail able The executable installers are out of date or for whatever reason do not work Then if you can get the Tcl interpreter to run on your machine you can run the instrument source code The source code is written in the Tcl pronounced tickle language T...

Page 27: ...e 5 Select Browse This brings up a file selector dialogue 6 Now find the WISH84 icon on your desktop Right click on the WISH84 icon select Properties to determine the location of the WISH84 program 7 Copy that location into the previous Browse dialogue Now double clicking on any file with the tcl suffix will cause it to be executed by WISH 7 Commands Cautionary Note The CTR 201 Curve Tracer is des...

Page 28: ... bit value between 0 and 4096 eg S 404 see Note B set the upper base voltage eg B 348 12 bit value between 0 and 4096 Sets the source output current at the Base terminal See note b set lower base voltage eg b 0 12 bit value between 0 and 4096 Sets the sink output current at the Base terminal See note P base driver high current set point v set Base drive mode to voltage c set Base drive mode to cur...

Page 29: ...es Setting external voltages accurately relies on a y Mx B correction in the calibration memory Operating the calibration control panel and observing the message traffic we obtain the following messages for various outputs Collector Voltage 10V D 404 20V D 1451 40V D 3544 Emitter Voltage 10V S 404 20V S 1458 40V S 3565 Base Voltage 10V B 1090 20V B 1828 40V B 3304 Example h Set low current range f...

Page 30: ...rt and Import Data Compare Measurements Under the Data menu there are now three entries Export Curve Data to CSV This selection saves the measurement results to a CSV comma separated value file A CSV formatted file can be read by any text editor and imported into a spreadsheet or plotting program like gnuplot Load Reference Curve This selection loads and plots the data from a previously saved CSV ...

Page 31: ...This option was provided to a customer to minimize power dissipation in the device under test With this option selected the measurement of each point should be about 7 5ms long The curve may be a bit noisier as we are doing less averaging in the firmware 28 ...

Page 32: ...htb Figure 24 48V Power Enable Disable 29 ...

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