FEC VF40CM
The VF40CM is intended for testing VF, HALF CYCLE SURGE, and THERMAL RESPONSE/RESISTANCE on small and medium power diodes and rectifiers. It can also measure THERMAL RESPONSE/RESISTANCE on NPN and PNP bipolar transistors using an external user supplied VCB supply.
The VF40CM is also capable and is sometimes used to measure VZ of low voltage zener diodes up to the compliance voltage limit of the tester. 20V at 20A is possible.
The tester can be used alone, programmed by its built-in keypad and LCD display or it can be programmed remotely with a PC. We supply at no extra charge a very powerful software program (VFS2) for your PC that can produce many useful plots or datalog files. Also supplied is another program (STATS) that produces statistical reports using data captured by VFS2.
HARDWARE OVERVIEW
A programmable constant current power supply/pulse generator provides the forcing current pulses for all of the tests including the IM current for the Thermal tests.
A 14 bit Analog to Digital converter with a dual scale differential input amplifier reads the VF of the device under test
The tester is controlled by a micro-controller with our VF40CM firmware. It can remember your test setup if you wish in its non-volatile EEPROM. The VF40CM firmware is contained in a plug-in EPROM that can easily be changed if we add or change features in the future.
The VF40CM contains an interface that can communicate with diode handlers for production testing. In this case it is usually used with an optional external orienter to accommodate diodes presented with random orientation.
TESTS PERFORMED
VFThe VF readings are (as with all the other tests) displayed, passed on to the optional PC and compared to programmable test limits to produce go-nogo results or “bin sorting”.
SURGESURGE is similar to VF except that the current pulse is an 8.3ms half sinewave. The VF is sampled at the time of the peak current.
DVFThis Thermal test reports the delta VF before and after a “heating pulse” of current (IH) with a pulse width (TH). The current at which the delta VF is measured is a lower current (IM). A sampling delay (TMD) occurs after TH and before sampling of the “hot VF”. All of these parameters are programmable.
THETAThis Thermal test is the same as DVF but the results are reported as °C/Watt. In order to do this calculation, we ask you to enter a value for the “K Factor” in terms of mV/°C. In standard terms this is actually 1/K.
TRThis is THERMAL RESISTANCE and is the same as THETA except that it is done with a very long TH so that the junction temperature has time to reach equilibrium.
SCALES
The forcing current scales are 0- 40.00mA, 400.0mA, 4.000A, and 40.00A.
The voltage readout scales are 0-1.6383V and 0-24.574V
POWER SUPPLY DERATING
The tester supplies 5A for any pulse width.
At 8A the maximum TH is 50ms
At 20A the maximum TH is 25ms
At 40A the maximum TH is 10ms
ABOUT THE PC SOFTWARE
The software provided, VFS2 and STATS for use with an optional user supplied PC are DOS programs. They can be used with DOS or with WINDOWS any version up to WIN98. They are not recommended for WINDOWS XP, 2000 or VISTA.
FEC can supply a suitable PC at extra cost that runs a version of DOS called FreeDOS which is distributed free under GPL licensing.