Playing with the semiconductor curve tracer I did a quick test of potential candidates for diode cathode bias:
The popular HLMP-6000 is a superb LED with its low impedance. The SiC diodes have proved to be a great match with an impedance lower than 2Ω. Bias voltages will be around 0.7-0.8V for low currents. The classic Schottky SB540 has a very low impedance, but its forward voltage is so low that is not practical for diode cathode bias. What surprised me was to see the 1N4007 to be a good match. The impedance is higher than the LEDs or SiCs, but good enough. The green LED on the opposite extent has a significant dynamic resistance over 10Ω.
Interesting to see that a minimum of 2mA should be run through with small signals to ensure the diode operates in the linear region. The higher the better. An arrangement with an extra source of diode current (e.g. LND150 or DN2540 CCS shunting current to the diode) can be used when dealing with lower cathode currents due to the valve being used.
Further tests are required….
Hello Ale, have been playing with the C3D02060 a lot with great success. I found a pile of C4D0212s on the shelf and have been wondering about them and which other SiC might work for bias as well. Might you have tested or considered any others?
Hey Chuck. I played with a few and settled with the C3D02060 as sounded best for me. Most of the SiC HV parts sound very well in my opinion. You just need to experiment and listen. Would be great to hear further feedback and exploration around this topic. I’m struggling with time to test many of the things I want!
Hope summer is going ok in France. Take care!
Ale