variable zener

LLIJ variable zener One of the problems encountered in developing circuits is the selection of correct values for various compo- nents. Often trial-and-error is used to find the most suitable value for a particular circuit. There is, however, one major problem with this method of selecting values; most people who build electronic circuits as a hobby do not have vast quantities of com- ponents to cover all the various 3...25 V 500 mW 7-88 values which might be needed. And, of course, there is always Murphys law to consider: you always have every value of component possible P1 — except the one that you need. So, 250k R3 having been "bitten" (not literally) once again by Murphy, we came up 557B with a design for a "zener diode" with Ti variable zener voltage. Compared to "normai" zener diodes, Ri is some- 82 what higher (20 ... 50 S2), the maxi- 5478 mum load lower and the temperature coefficient less ideal (about — 2 mV/ °C/0.6 V). The circuit is, however, quite straightforward...