Using Zener Diodes (Part 1) - Voltage Regulator and Zener Theory

[Music] hello again and welcome to simply electronics today's video is about voltage regulation with Zener diodes if you take a look at the breadboard here you can see that I've got a Zener diode regulating to a voltage of five point one volts from a 12 volt input so this video will explain how you can create your own voltage regulator using just a Zener diode and a resistor using a Zener diode as a voltage regulator is the simplest and cheapest way to regulate voltage however they are pretty much the least efficient voltage regulation method so the practical uses of Zener diodes tend to be for lower current applications such as creating reference voltages or a low current supply to an IC before we get started go ahead and watch my previous video on the basics of Zener diodes so that you can get a better understanding of how a Zener diode differs from a normal diode now before we go ahead and get started on Zener diodes I want to talk about normal diodes normal diodes as we know will conduct in one direction but will not conduct when they are reversed biased so I've got a diode on this board with a resistor to limit the current through the circuit so my orange and white cable here is coming straight from this 12 volt power supply onto the board so the orange is positive and the white is negative so I'm going to go ahead and do is connect the orange cable to the positive side of the diode obviously there is a resistor before it to limit the current and then I'm going to connect the negative wire to the cathode of this diode this normal diode is now placed in the circuit in its forward biased direction with a resistor only to limit the current meaning that this diode will conduct current through this circuit if we measure the voltage across this diode we can observe that there is a voltage drop of 0.6 volts across it this is because the diode has a certain resistance in its forward biased direction and most styles will have a 0.6 to 0.75 waltz drop across them because of this internal resistance so I'm supplying 12 volts to this circuit so keep in mind that this voltage indicator is actually 0.4 volts out there is actually 12 volts going to the circuit not twelve point four but either way I have 0.6 volts across this diode and because of kirchoff's law which to put it simply basically states that all voltage drops in a circuit will always add up to the input voltage so we've got 0.6 volts dropped across this diode so we can expect that there will be 12 volts minus the 0.6 volts across this diode so we can expect that the voltage across this resistor will be the input voltage minus the 0.6 volt drop across the diode so let's check that out okay so the voltage across that resistor is pretty much eleven point four volts because 0.6 volts is being dropped across this diode and just to prove to you that there is current flowing through this circuit with the diode in this direction you can see on the multimeter I've connected it in series with the circuit and you can see that there is 55 milliamps flowing through the circuit with the diode in that direction so now let's reverse the direction of this diode and basically reverse bias it and then we'll observe what happens so let's go ahead now and measure the voltage across that diode again see if you can have a guess what the voltage will be across that diode when I measure it okay so let's measure it and see what the voltage is and there you go we've got 12 volts dropped across that diode and what this means is the voltage that we are supplying to the circuit that voltage is all being dropped across that diode so there will be no voltage dropped across anything else within this circuit so if I go ahead and measure the voltage across this resistor you can see there is zero volts to this resistor and this is because the voltage is getting to the diode but the diode because it is reverse biased is blocking any current from flowing past it so one thing to note is there is a limit to how much voltage a normal diode can drop before it breaks down and starts to conduct because we basically damage the diode and I think this one is about 600 volts if we put more than 600 volts across this diode it will break down and allow current to flow through even when it's reverse biased and that is known as the breakdown voltage of a diode now I don't have 600 volts that I can go and throw through this diode to demonstrate that but what I do have is a Zener diode and this is where things get very interesting Zener diodes are engineered to have a specific breakdown voltage so that when we reverse bias a Zener diode they will break down at a certain voltage and start to conduct and you will know this if you see my previous video on Zener diode so first of all I'm going to put this diode in a forward bias direction meaning it will allow current to flow through this circuit no matter what the voltage is so let's go ahead and measure the voltage across that and we can see there it's dropping about zero point seven nine volts so this Zener diode is dropping a slightly higher voltage than our normal diode but that's fine this is allowing current to flow through the circuit and it's dropping a certain voltage just like the normal diode we just used so this is dropping 0.8 volts across it allowing current to flow through the circuit and the only other component in the circuit is the resistor so the resistor should be dropping 12 volts minus 0.8 so we should have eleven point two volts across this resistor and there we go we've got our eleven point two volts across that resistor so the total voltage in this circuit is 12 volts so current is being allowed to flow through the Zener diode through the resistor and back to the power supply now let's have a look what happens when we turn this diode around and reverse bias it now I've turned the voltage down to ten point seven volts I have the multimeter connected in series with this circuit so that you can see the current measured in milliamps at this point now that diode is currently blocking any current from flowing through this circuit because it is reverse biased now watch what happens keep your eye on the multimeter display and the power supply display and watch what happens as I go above 12 volts you can see eleven point five 11.7 and above twelve volts and the diode starts to conduct current and that is the reverse breakdown voltage otherwise known as the Zener breakdown voltage of this Zener diode that Zener diode has a specific reverse breakdown voltage of 12 volts so it starts to conduct current as the power supplied to it goes above 12 volts and if we go back below 12 volts you can see no current is flowing through the circuit now let's take a look at something pretty cool about Zener diodes look at the voltage being supplied it's ten point seven volts although this voltmeter is slightly out so we're actually at ten point four volts but watch what happens when I increase the voltage keep your eyes on both of these displays I increase the voltage when our we're now at about 12 volts and watch when I increase the voltage we're going up towards 14 volts and all across the Zener diode we still have about eleven point seven volts so this Zener diode has started to regulate the voltage across it because we're supplying 14 volts and we're getting about eleven point eight because there is a percentage error with these Zener diode we're getting eleven point eight volts across it so where has that extra two point two volts gone well it's being dissipated by this resistor any voltage that that Zener diode doesn't want it shunted out to any other component in the circuit in this case we use the resistor to drop that additional voltage so if we have eleven point eight volts across this Zener we should have the remainder of that voltage across this resistor okay so let's measure the voltage across the resistor and you can see we've got approximately 1.8 volts across that resistor so the voltage being dropped across the Zener diode is roughly 12 volts and the voltage being dropped across this resistor is roughly 2 volts so that's what's happening the Zener diode regulates the voltage by sending any additional voltage to that resistor and let's take a look and swap this Zener diode out for a 5 point 1 volt Zener diode and take a look at the voltage across it there we go we've got five point one volts so the five point one volt Zener diode does exactly the same as a 12 volt Zener diode it regulates to its Zener break down voltage so the Zener diode is reverse-biased and it's dropping five point one volts so the resistor must be dropping the rest of that voltage so let's take our input voltage of 14 volts which is probably about thirteen point five the Zener diode is dropping five point one so the resistor must be dropping thirteen point five minus five point one volts so the resistor must be dropping around eight point four volts so let's measure the voltage across it and there we go then on eight point four volts so yeah that display is point five volts out and so that is how it works the Zener diode regulates the voltage across itself this is very much like a voltage divider circuit except the Zener diode essentially changes its own resistance to make sure that five point one volts is always dropped across it and this is the same for any Zener diode it will always regulate at its center breakdown voltage because the rest of the voltage is sent to the resistor and dropped by that resistor you

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Keywords: electronics, basics, current, electric, electron, flow, tutorial, how, to, energy, hobby, multimeter, power, circuit, volts, amps, watts, solder, iron, soldering, simple, simply, making, bigclive, big, clive, bigclivedotcom, diy, hack, How to use a zener diode, how to use zener diode, what is a zener diode, zener theory, zener diode theory, zener diode circuit, zener diode regulator, zener diode regulation, voltage drop, calculate voltage drop, reverse breakdown, zener voltage, zener breakdown

Id: E4IIiIhIYAg

Length: 11min 7sec (667 seconds)

Published: Sun Dec 11 2016