Extra Measurements

DCA55‑equivalent and leakage measurements

Both run automatically after a saved identify (switches in Settings) or on demand from their card under the result.

DCA55‑equivalent (transistors)

The DCA75 tests hFE at about 5 mA collector current. The Peak DCA55 tests at Ic = 2.50 mA with Vce between 2 and 3 V (from Peak's DCA55 user guide) and subtracts leakage, so its figures are lower for many parts, especially germanium. Sightings reproduces those conditions with the curve tracer: it holds Vce at 2.5 V, servos the base current until Ic reaches 2.50 mA, and reports

• hFE (DCA55) = (Ic − leakage) / Ib at that point, with Ib and the measured Vce;
• Vbe at that point, and Vbe with about 4.5 mA forced into the base (an approximation of the DCA55's device‑dependent Vbe test);
• Ic leakage with the base open.

The DCA75's own figures are unchanged and shown alongside. Example: a 2N5088 read hFE 405 at 5 mA and 410 at 2.5 mA; an MP40A germanium PNP read 29 at 5 mA and 25 at 2.5 mA.

Reverse leakage (diodes and transistors)

The unit's normal current path floors at about 1 µA, far above silicon leakage. Sightings instead routes the junction's cathode through the unit's 470 kΩ gate resistor and reads the current from the voltage across it — the path the unit uses for base current — giving a few nA of resolution. A zero‑volt baseline is subtracted to cancel channel offset.

• Diodes: Ir at 5 V and 10 V.
• Transistors: Icbo, the collector–base junction with the emitter open, at 5 V and 10 V, shown next to the DCA75's own Iceo figure.

The DAC is servoed so the junction really sees the requested voltage; a leaky part drops volts across the 470 kΩ, and if the 12.5 V DAC ceiling is reached the card reports the voltage actually reached. Current can never exceed ~25 µA, so zeners and LEDs cannot be harmed.

Examples: a silicon diode read 5 nA at 5 V; a D9B germanium diode 2.9 µA at 5 V; an MP40A's Icbo 2.9 µA at 5 V against 31 µA of Iceo.

Both sets of figures are stored with the reading and appear in bin statistics, so a bin of germanium transistors can be sorted by leakage or DCA55 gain.