FEC VF40CM Diode Tester

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 also 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.

VF40CM 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

• VF The 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”.
• SURGE SURGE 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.
• DVF This 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.
• THETA This 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.
• TR This 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