This video is about this component which is called a Zener diode and I built this circuit to help me investigate it. Here is my Zener diode symbol and as you can see it's a regular diode with a little tag on the edge and I've got a power supply not in the camera where I've got the positive here so current is going to go this way. This is forward biased. The name of this diode is bzx850c5b6 and the Z indicates that it's a Zener diode. Let's see what it does when we apply a voltage. I press play on my data logger. I'm increasing the voltage as you would expect not a lot is happening and then the current increases. This is acting like a regular diode. If I draw the graph we've just got on the screen there. It goes along here. It goes up like that. This voltage is around about 0.7. This is the voltage axis. This is the current axis and I was taking around about 400mA. So in forward biased the Zener diode acts exactly like a regular silicon diode. What I've done now is I've reversed my Zener diode. I've turned it around like that and the symbol on my diagram is now the other direction. So this diode is now reversed biased. I'm going to increase the voltage again and we'll see what happens and we would expect if it was a regular diode for nothing to happen. So let's have a look. So I'm increasing my voltage and I've already got to 1.5 volts and there's no current flowing. I keep going to 2 volts, 3 volts, 4 volts and when I get to 5 volts I'm going to be quite careful here. We see what happens is that the Zener diode starts to conduct. Now that's quite unusual because that means this diode is conducting backwards. If I were to draw my graph like I did before I would get almost the same shape as I had last time. This is again the voltage axis but this time the voltage that it's conducting at is much higher. In fact it's around about 5.6 volts and my current is a very similar value. Now I don't know if you can see but in the name of a Zener diode it has 5d6 which means 5.6 volts. So a Zener diode is a diode that conducts in reverse bias at a very specific voltage which is very useful. Finally we'll try and put all our information together onto one graph. So my Zener diode is now returned to its original orientation. I'm going to be looking at the forward bias part of the graph first. So I'll turn on my power supply and here we go. You see the current is moving along. The voltage is moving along the axis and then current starts to flow when the forward bias voltage gets to be about 0.7 volts. I'm turning the power supply back down again. Now rather than turning the diode round what I'm going to do is swap the connections on the power supply which the data level will interpret as being a negative voltage. So you see it's rescaled now. I'm going to increase the negative voltage. So I'm going back along the voltage axis. So I'm up to minus 1. Minus 1.5 and as you can see no current is flowing and if I keep going the graph will keep rescaling until I get to the point where it's going to start conducting in reverse bias and there it goes. So if we put that onto our own graph what we have is the forward bias section. We have the graph of a silicon diode which looks something like that and this here is labeled as 0.7 volts. I'm not under any obligation to use the same voltage scaling in that direction as I do in that direction. So I'm not going to in text but it's often done either. So I'm going to go along the axis here and then at the zen of voltage I get a nice sharp downward curve. This indicates that current starts flowing in reverse bias at in this case 5.6 volts and I'm going to label this as negative as on my data logger. So that's the full graph for the zen of diode.