Okay, today we are going to talk about a half wave rectifier circuit.
Now one of the first things we need to know before we jump into the half wave rectifier
circuit is what is the point of half.
Wow, that is quite the mouthful of a half wave rectifier circuit.
Now there are a couple of different ways that you can convert AC to DC.
And a half wave rectifier is a portion of one of the easiest ways to do that.
Now there's actually quite a few steps to get a good DC signal first usually transform
the AC line voltage to what you're typically going to need which is generally in the five
to 20-30 volt range, then you rectify it which is what we'll be talking about here.
Then you filter which will touch a little bit today and then finally you regulate it
which will do any future tutorial but we are going to be going over the rectification the
transforming and then a little bit of the filtering today.
So to start with we have the transformer here and the transformer is a Triad VPS24-5400.
This is vastly oversized for what we needed, but this is something that I have left over
from a project that I did a couple of years ago, this can actually do 130 volt-amps.
And we're only going to be using a little bit over a 10th of a watt.
So yeah, way oversized, but it's big enough that hopefully it's easy to see.
And then once we take the power and transform it down to a level that is a little bit more
reasonable.
In this case, we're taking it down to 12 volts RMS, it's going to be about 20 volts peak
to peak, we're going to run it through this diode, which is going to rectify and make
it so it is only a DC signal.
We're going to look at it on the oscilloscope a little bit, see what that looks like.
And then we're going to throw in some capacitors to act as filters.
So you can see how important these are.
And just for your information, this is a 15K resistor.
So that's the load that we have, which is going to make it so we don't have a huge amount
of power and as that load changes, the amount of capacitance you need to properly filter
something is also going to change going back to the transformer.
We have it set up here this is setup in parallel.
So we are going to have about 110 - 120 line voltage going in, and we're going to have
12 volts coming out, I don't want to spend the time to go into series versus parallel.
But if you are doing something with a transformer, look at the way it's set up and make sure
it's actually set up to give you the output voltage you want.
So now I'm going to turn on the telescope and I'm going to plug in the transformer and
we're going to see what it looks like and then we're going to throw those capacitors
in there, and we're gonna have a good time.
So let me do that.
Okay, so it's plugged in and the oscilloscope has been turned on.
Something that I want to point out really quick is now that this transformer has been
plugged in, and this is lines voltage, I have 110 - 120 volts right there AC.
So that's pretty dangerous.
If you are going to do this at home, be very, very careful.
If you're not comfortable, always have somebody with you take the proper precautions, cover
it up, do something like that.
I didn't want to cover this up because I wanted to show it off.
There is a reason I typically work with low voltage embedded systems versus this sort
of stuff.
That sort of stuff just makes me nervous.
I have a past history.
I'm not going to go into it right now.
But I do not like getting shocked and I highly recommend you don't do it either.
It's really unpleasant.
So we have about 20 volts coming off of these two leads, and it's a fully AC signal.
But what I'm measuring here on the oscilloscope is actually what this load resistor is seeing,
I've connected to the output of the rectifying diode.
So as you look over here, you can see that the load is seeing no voltage, and then it's
seeing a peak, and then no voltage, and then it's going up to a peak.
Now, even though it's changing, it's not alternating direction because it never goes in the negative
direction.
So this already is technically a DC signal, because current is always flowing in one direction.
And that's because the diode is stopping the flow from coming back in the other direction.
So that's kind of the funny thing.
If you want to technically get a DC signal, we already have done that with one component,
and that is the diode because all of this is flowing in the same direction.
Now this isn't very useful if you have something that's zero volts and then goes up to 20 volts
and it oscillating, again, not oscillating, because it's always positive.
But it's doing that 60 times a second.
That's not really going to be consistent for whatever embedded system or device you're
trying to charge, whatever.
So we're going to have to do something with that in that is where the filtering comes
in.
So I have here a 4.7 microFarad and a 2200 microFarad capacitor.
These are both electrolytic and they're both rather large.
But I'm going to turn this off really quick.
Put in the small one and we're going to see how this changes.
Once we have a small capacitor in there.
Think I need to actually turn that off so long as I do this, right.
Don't put that in backwards.
Okay, now that we have the capacitor in here, you can see that the waveform looks significantly
different.
And right now since it doesn't ever come down, I need to change my trigger point.
So that it stops and gives me a good... there we go.
Now we have a good reading.
But you can see that we're still peaking at 20 volts, and then the capacitor is getting
charged.
And then the load is slowly decreasing the charge in that capacitor before the incoming
voltage increases, recharges the capacitor and then it drops off again, comes up in discharges.
So this is actually a perfect size to show what a small ripple looks like when you're
doing your rectifier circuit.
So this is still not ideal because since these are 10 volts per division, that is a five
volt drop 60 times a second.
So that's not fantastic.
But it shows still what the waveform looks like at a very visible level.
So now that we've done that with 4.7, let's do 2200 and that should go away completely.
So pull this out.
That is probably still charged.
Okay, now that I have the 2200 microFarad capacitor plugged in.
You can look over here at the oscilloscope and see almost no jitter whatsoever.
It's perfectly flat.
Again, it's a 15,000 ohm resistor in there.
So that's a pretty small load.
And that's a pretty big capacitor.
One of the drawbacks of having the capacitor this big is that it takes longer to charge
in the first place.
So there are other ways to make this smoother than just increasing the capacity is there
certain tricks, but this is pretty brute force.
Easy way to just make it so you don't have as much ripples, just putting in a bigger
capacitor.
Okay, as we're sitting here, you can see it's this high, but I'm going to just I'm going
to flat out, unplug this.
And you'll see how this low we dropped.
And so instead of before where we are getting kind of that up, down, down, it'll just slow
we drop showing exactly how much energy and how much power is being stored in this capacitor.
So let me unplug this really quick.
Now you can immediately see that it's starting to drop slow.
Slowly, slowly, but again at 10 volts per division that looks like it's dropping a half
volt to a volt per second.
But if we had done that with the, the 4.7 microFarad capacity, it would already be diminished.
I mean, we were dropping five volts in a 60 of a second.
So this is definitely holding much, much more.
So this is how a half wave rectifier works.
Again, it's super inefficient in regards to originally we had just the one way form and
then nothing one way form in the nothing.
And so you're losing half of your power right there, we can do a full wave rectifier, which
is a lot more effective, a lot more efficient and not a whole lot more complicated.
And that will give you much, much better results.
But we just wanted to go over the half wave rectifier to show you how you can use one
diode to get a DC signal.
So transform it, rectify it, filter it, later we'll talk about regulating it so you get
exactly the voltage you want all the time.
And that's going to be super exciting.
But that's all we have for today for the half wave rectifier circuit.
I hope you enjoyed this hope this practical demonstration of how simple it is and how
effective it is is helpful to you in some way.
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