The reason 6.2v is a magic number for zeners is this:
There are two modes of "Zener" diode operation. The first, the true Zener range works from about a volt to maybe ten volts or so, where it becomes insignificant. The second, more common range is the avalanche mode, which becomes increasingly important from around five volts plus. Most "zeners" are actually avalanche diodes.
The reason for the tempco stability is that the Zener effect has a positive tempco and the avalanche effect has a negative tempco. At around six volts, the effects cancel out. Neat, huh?
With both modes of operation contributing equally, the Zener has its lowest noise at this voltage.
Hope this helps,
Bob McIntyre
There are two modes of "Zener" diode operation. The first, the true Zener range works from about a volt to maybe ten volts or so, where it becomes insignificant. The second, more common range is the avalanche mode, which becomes increasingly important from around five volts plus. Most "zeners" are actually avalanche diodes.
The reason for the tempco stability is that the Zener effect has a positive tempco and the avalanche effect has a negative tempco. At around six volts, the effects cancel out. Neat, huh?
With both modes of operation contributing equally, the Zener has its lowest noise at this voltage.
Hope this helps,
Bob McIntyre