For an ideal diode, no current at all passes when the voltage is less than zero: the diode completely prevents reverse current flow. If we hook up a diode in a simple circuit with a variable voltage source and a current-limiting resistor, we can measure the current I through the diode when a given voltage V is applied across it. Surface mount versions of diodes tend to follow the same labeling convention, where the cathode end is marked with a broad stripe. The schematic symbol is a triangle pointing towards a bar, where the current flows in the same direction, towards the barred (striped) end. In a perfectly ideal diode, current flows in one direction only, from the anode (positive side) to the cathode (negative side) which is marked with the stripe. And, while there are many different types of diodes– see here for a long list –we’re going to focus on so-called “normal” semiconductor diodes, most commonly constructed with a p-n silicon junction.ĭiodes usually come in glass or plastic cylindrical packages, marked with a stripe on one side to indicate polarity. To understand how Zener diodes are different from other diodes, let’s first review the properties of regular diodes. In what follows, we’ll show you how (and when) to use a Zener, for applications including simple reference voltages, clamping signals to specific voltage ranges, and easing the load on a voltage regulator.īackground: Semiconductor diodes, real and ideal And while that sounds a bit esoteric, they’re actually among the handiest components ever to cross an engineer’s bench, providing great solutions to a number of common needs in circuit design. Zener diodes are a special type of semiconductor diode– devices that allow current to flow in one direction only –that also allow current to flow in the opposite direction, but only when exposed to enough voltage.
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