Arvo wrote:

crankyhobo wrote:

low voltage zeners produce no heat

Ahem, little nitpicking required

Of course zeners produce heat, in this circuit exactly like an ordinary resistor (or some diodes in serial). Heat output (power) can be calculated as P=U*I, where U is voltage drop and I is current.

For 5V and 80mA we get 5V*0.08A=0,4W.

There are zeners up to 50W (and probably more, I checked only 'local' online store) available, they're a bit expensive though.

Interesting, i got this idea from the wikipedia article on zener diodes, which says:

**Quote:**

In silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.

In a 5.6 V diode, the two effects occur together and their temperature coefficients neatly cancel each other out, thus the 5.6 V diode is the component of choice in temperature-critical applications.

Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients, but as higher voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode.

Sounds like i misinterpretted it.