A Zener Diode with No Resistor? It Overheats

A Zener diode is connected in reverse on purpose. Near its Zener voltage, a small rise in voltage makes the reverse current increase a lot, and that's what limits how high the output can go. It's built to work in the breakdown region, within set current and power limits. Don't connect a Zener by itself directly across the power supply. A stiff supply above its Zener voltage can force a huge current, and the part overheats. So a resistor goes between the supply and the output to limit the current. In the video, the band end (cathode) goes to the output and the other end to 0V. With a 9V supply and a 390Ω resistor, and assuming the output stays at 5.1V, the resistor has 3.9V across it and about 10mA flows. With no other load, all of that goes through the Zener. If a load draws 3mA, roughly 7mA goes through the Zener. This is a simple calculation to show the idea. If the load draws too much current, the Zener doesn't get enough, and the output voltage can drop. The labeled voltage is specified at a set test current, and in practice it varies with current, temperature and part tolerance. Use a current limiting resistor, and check the current and heat too. #zenerdiode #diode #electronics #electronicsbasics #insideembedded