Electronic Basics #9: Diodes & Bridge Rectifiers

diodes are everywhere just take a look in any power supply you own the old linear power supplies have them four of those to be exact and the newer switching power supply still have them consumer electronics consist of them as well here's a small SMD diode on the banana pie but why are those diodes so important and how do we use them we will find it out let's take a look at DC Circuit's first where current only flows one way like this LED blink circuit i connect +5 volts to the upper terminal and ground to the other now everything works fine but if you have a little bit too much of something or one of those ridiculous power plugs where you can easily screw up the polarity it can happen that you connect your power the other way around and your circuit will not like that and probably get destroyed a diode can prevent that if we connect +5 volts to the anode of the diode and the cathode to the upper terminal then we can power our circuit like normal and see that everything works fine but if we reverse the polarity again we can see that no current will flow because a diode is only conductive when positive voltage is applied to the anode and ground to the cathode but now diode is perfect when we take a look in the datasheet of this one n400 7 we can see that there is a voltage drop across the diode which is determined by the current draw which means that we apply five volts at the circuit input here but our main useful circuit only gets four point three five volts that is something you have to keep in mind when designing the circuit and that also means that we generate wasted power with the diode in this case only 4.5 five milli watts but still thirteen percent of the used power but when our loads draws a lot of current things can get hot and you have to upgrade this one amp diode to a bigger one or an even bigger one or a massive one since diodes let current flow only one way it is great to convert AC to DC and we are not talking about a rock band or something here I'm using a 220 volts to 50 volts transformer to work safely with mains power you can see the sine wave on the oscilloscope but wait it says twenty five point six volts max voltage I bought it as 15 those values are always given as RMS values or root mean square values you can calculate those mathematically but for the sake of simplicity you can divide the next voltage by the square root of two only for sine wave though but that is still 18 volts yeah but only when there is no load attached if I draw some current the voltage collapses and will eventually reach 15 volts RMS okay let's put our diode in serious and yes let is DC horrible bumpy DC but still only positive voltage we could use this to build our own TC power supply I just added a capacitor and voila perfect DC but when we draw just a bit of current we can see that it gets bumpy again it really sucks that those negative waves are gone because the cap can only be charged with the positive ones and then it gets discharged until the next wave comes I wish there would be another wave to charge it up sooner but wait we can do this the schematic for bridge rectifier looks like this which is correct but I think if I draw it like this it is easier to explain firstly pluses here and negative is here of course current wants to flow from positive to negative and it can only flow through the anode of a diode to the cathode so for this polarity current choose this way now we change the polarity on the input and try to complete the current circuit again and there it is and did you notice that no matter how the polarity of the input is the output current flows only one way that is the whole trick this way we turned our negative sine wave into a positive and we can build more useful power supplies I think this is enough for the first introduction to diodes but keep in mind that there are plenty more types to talk about I hope you like this video as always you can support my videos by like and sharing them stay creative and I will see you next time

Channel: GreatScott!

Views: 348,288

Rating: 4.9647489 out of 5

Keywords: Electronics (Field Of Study), Rectifier, Diode Bridge, Diode, bridge rectifier, general purpose diode, DC, direct current, AC, alternating current, greatscott!, DSO, oscilloscope, digital, mains power, sine wave, transformer, 1N4007, 1N400, linear power supply, switching power supply

Id: 46WSCihjoRI

Length: 5min 10sec (310 seconds)

Published: Fri Sep 26 2014

Reddit Comments

[u/trollingxchromosomes]

This video is concise, understandable and educational. I like you.

[u/Sharp6]

Just this weekend, I was thinking about ordering a bridge rectifier or trying to 'build' one with diodes (I'm trying to get 5v DC from my 6v AC dynamo). Thanks to your clear video, I will try to make one myself!

[u/AnathemaFan]

It's also just what I need because I want to build one. How apposite, thanks!

[u/saimis]

now i know how diode bridge works not only what it does. thanks!

[u/[deleted]]

What is the average education level of people in this sub? Because this is 100 level EE class info.

[u/gnu_bag]

Good, concise explanations. Keep it up!

[u/kacxdak]

I have a test on this on Thursday. Thank god for reddit