in this video i'm going to talk about zenerdiodes, and how you can use them to protect your circuitsfrom sudden voltage spikes, and how you can use them as cheap voltage regulator. you caneven use them as part of an audio distortion circuit!let's get started. the first thing to know is that the circuitsymbol for zener diodes looks very similar
Triangular Solar Panels, to other diodesymbols. make sure you don't get them confused because they behave very differently, andthey are used for very different things!so what's special about zener diodes? well, with a regular diode current can flow in onlyone direction.
but zener diodes can actually allow currentto flow in both directions! this may sound confusing at firstbecause the whole point of a diode is to only allow forward current, but i promise you theyare useful. think of zeners like this. they are kind oflike two diodes in parallel, facing in opposite directions, eachwith different voltage drops. when you try push current in this direction through thezener diode, there's a forward voltage drop that is typicallyaround 1v. the diode won't even turn on and allowcurrent to flow unless you have at least 1 volt. when the zener is on in the forwarddirection, we say it
is "forward biased". but going the other way,there's a different voltage drop, called the zener voltage,or vz. in this example it's 3.3 volts. this zener diode will not allow current to flowin this direction until there is 3.3 volts across it. but, once thereis sufficient voltage, the current can flow in this direction,and you will get a constant voltage drop of 3.3 volts. since current is flowing backwards,we say the zener diode is "reverse biased". this propertyof having a predictable voltage drop is what makeszener diodes useful. if you set your circuit up just right, you can use zener diodes tolimit the voltage
that other devices receive.let's say you have a circuit that has a voltage input, and you are worried that youmight destroy it with too high a voltage. it could be a microcontrolleror an op amp that can only handle 3.3 volts on theinput, and sometimes the voltage reaches 10 volts, or even -10 volts! you can use the classic zener voltage clampingcircuit to solve this problem. it's just a resistor and azener diode in this arrangement. this circuit will "clamp" the voltage to a maximumof 3.3 volts and a minimum of -1 volt. let's see how it worksin real life.
i'm using my wave generator here to generatea triangle waveform that goes from -10 volts to + 10volts. for this example, the frequency doesn't matter.on the breadboard i have a 1k resistor and a 1n5226 3.3v zener diode. i'm feeding inthe -10 volt to +10 volt wave, and i am measuring the clampedoutput on my oscilloscope. over here when the input voltage is -10 volts,there's enough voltage to forward bias the zener diode.some current flows through the zener diode, and some flows from the output. the forwardvoltage drop is 1 volt, so it effectively clamps theoutput voltage to -1v. now, between -1 volt
and 3.3 voltsthings get interesting. there's not enough voltage to turn the zener diode on in eitherdirection. so it's like the zener diode doesn't even existin the circuit. current flows straight from the input, throughthe 1k resistor to the output. because of this, the input voltage and the output voltageare exactly the same.now when the input is above 3.3 volts we have enough voltage to fully reverse bias the zenerdiode. current flows through the zener in this direction,and some current also flows to the output. since thezener voltage drop is 3.3 volts, the output
voltage gets limited to 3.3 volts, and ourvoltage sensitive circuit is saved!for the musicians out there here's another example with an input sine wave that's between+ and - half a volt. the zener diode allows the signalto pass through relatively unchanged. now watch whathappens when we increase the amplitude of the input signal to 10 volts peak to peak.the output gets distorted! the top and bottom of the sinewave get clipped off and our output is swinging from -0.8volts to +2.6 volts. notice how that's different to the - 1 volt to +3.3 volts i was showingyou in the
previous example. that's because the exactvoltage drop across a zener diode will depend on theamount of current flowing through it. just the same as any other diode. anyways, thereare lots of different ways to use this technique, andif you search for diode distortion circuits you can find someexamples. so that was an example with a 3.3v zener diodebut you can get them with all kinds of zener voltages.now i want to show you an example with a 5.1v zener diode and how you can use it as a crudevoltage regulator.okay, so i've got my power supply set to
12 volts and on my breadboard i have itconnected to a 220 ohm resistor in series with a 1n5231 5.1 volt zener diode. this is enough to give you a low current, lowaccuracy 5 volt supply. i've got my electronic load connected so i can show you how the voltagechanges under load. with no load we've got 5.095 volts whichis what you would expect. if i increase the load to 20milliamps, the output drops to 4.954 volts. that's pretty good, and it would be enoughto power a microcontroller or some digital logic chips.but if we put a 30 milliamp load on it, all of a sudden we'vegot a significant voltage drop. and with a
50 milliamp load, it's completely useless.let's go back to a 20ma load and i want to show you how the input voltage also changesthings. on the right we've got my power supply's inputvoltage going into the zener diode regulator, and on the leftmy multimeter is showing you the supposedly regulated 5.1 volt output. if i change theinput from 12 volts to 16 volts, the output changes quitea bit. and going from 16 volts down to 8 volts, this regulatoris useless. you can partially solve the problem by choosinga different resistor value for the circuit, but in general,zener voltages change so much with current
and temperature that you should really beusing a linear regulator or a switch mode power supply foranything more than a few milliamps. alright, those are basics of zener diodes,and now you know how to use them to clamp voltages towhatever you want! just make sure that you don't use them for anything high powered. thank you for watching, and if you found thisvideo useful, consider supporting me on patreon - you'llget access to new videos 2 weeks sooner than everybody else!
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