Adjustable Zener Diode

A Zener diode is the simplest known type of voltage limiter (Figure 1) As soon as the voltage exceeds the rated voltage of the Zener diode, a current can flow through the diode to limit the voltage. This is exactly the right answer for many protection circuit applications.However, if it is necessary to limit a signal to a certain voltage in a control circuit, Zener diodes do not provide an adequate solution. They are only available with fixed values, which are also subject to a tolerance range. What we are looking for is thus an ‘adjustable’ Zener diode. Such a component would be useful in a heating controller with a preheat temperature limiting, for example, or in a battery charger to provide current limiting.