In this video I'll give you four essential tips for when you are using Zener diodes- get the best from them in your circuits and don't fall foul of any issues. Often the circuits are based around the shunt regulator and I'll use this as the basis for these tips.
First: remember they need to be current limited - don't just place them across a supply, they need a series resistor to limit the current. It's easy to calculate the value of the resistor needed. It's simply the input voltage minus regulated voltage divided by the current through the resistor.
Second: You need to run enough current through the diodes to get them to breakdown. If you don't run enough current though them then they won't give you the voltage they need. Often this is called IZT. The value is often about 7 mA for the standard low current types, so often about 10 mA is great. But check on the datasheet for your particular diode what the minimum current is. If you don't run enough through them they wont breakdown and give a regulated output. Also remember to leave enough margin so that when the load draws more, there's still enough to keep the diode operating as you want.
Thirdly: don't run too much current through the design. Make sure you keep it well within its rating. The power can be calculated by simply taking the maximum current the diode will pass and multiplying it by the voltage. Many small diodes have maximum power dissipation levels of 4 or 500mW, and small surface mount ones less. If you can run it at a maximum of, say 60%, then this will help the reliability
Finally: To get the best temperature coefficient if possible use diodes with voltages around 5 to 5.5 volts. There are two breakdown mechanisms in these diodes. Zener breakdown occurs below about 5 to 5.5 volts and above about 5 volts impact ionisation progressively dominates. As these two mechanisms have opposite temperature coefficients, selecting a diode with a voltage of between 5 and 5.5 volts gives the most stable temperature performance.
More information so you can understand about Zener reference voltage diodes and their uses in electronic circuit designs can be found at: www.electronics-notes.com/art...
Information about the theory of operation and breakdown mechanisms:
www.electronics-notes.com/art...
Information about linear voltage regulators including some Zener diode circuits: www.electronics-notes.com/art...
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15 апр 2024
