MC34063: One of the most common PWM (pulse-width modulation) controllers, plus a brief introduction to how DC-DC converters work.

A while ago, I published a review showing how to build a PWM regulator using a KR142EN5A. I also mentioned one of the most common and probably cheapest controllers for DC-DC converters: the MC34063.
Today, I'll try to add to that earlier review.

This chip is generally considered obsolete, but it's still deservedly popular, mainly because it's so cheap. I still use it from time to time in various DIY projects.
That's why I decided to buy a hundred of these chips. They cost me $4; the same seller now has them for $3.70 per hundred, which works out to just 3.7 cents apiece.
You can find them even cheaper, but I ordered these along with some other parts (see my reviews of a lithium battery charger and a current regulator for a flashlight). There was also a fourth component I ordered from the same seller, but I'll cover that another time.

Well, I've probably gone on long enough, so let's get to the review.
A quick warning: there will be lots of photos.
It all arrived in little bags, wrapped in bubble wrap. Quite a pile :)


The chips themselves are neatly packed in a resealable bag, with a label bearing the part number stuck to it. It's handwritten, but I don't think you'll have any trouble making it out.


These chips are made by different manufacturers and carry different markings.
MC34063
KA34063
UCC34063
And so on.
As you can see, only the first letters change; the numbers stay the same, so it's usually just called the 34063.
I got the MC34063 version.


Here's a photo next to an identical chip from another manufacturer.
The one under review has noticeably clearer markings.


I don't know what else I could review, so I'll move on to the second, more informative part of the review.
DC-DC converters are used in many places. These days, it's probably hard to find an electronic device that doesn't contain one.

There are three basic converter topologies. They're all described in the datasheet for the 34063, as well as in the application note and another description.
None of the circuits described here provide galvanic isolation. Also, if you look closely at all three circuits, you'll notice that they're very similar and differ only in the positions of three components: the inductor, diode, and power switch.

First, the most common one.
Step-down, or buck PWM converter.
It's used when you need to reduce the voltage while achieving the highest possible efficiency.
The input voltage is always higher than the output voltage, usually by at least 2–3 V. The greater the difference, the better (within reason).
At the same time, the input current is lower than the output current.
This topology is often used on motherboards. The converters there are usually multiphase and use synchronous rectification, but the basic principle is still the same: step-down.

In this circuit, the inductor stores energy while the switch is on. When the switch turns off, the voltage across the inductor (due to self-induction) charges the output capacitor.


The next circuit is used a little less often than the first one.
It is often found in power banks, where it converts the battery voltage of 3–4.2 V into a regulated 5 V.
This circuit can also produce more than 5 V, but keep in mind that the greater the difference in voltage, the harder the converter has to work.
This solution also has one not-so-pleasant drawback: the output cannot be turned off “in software.” In other words, the battery is always connected to the output through a diode. Also, in the event of a short circuit, the current is limited only by the internal resistance of the load and the battery.
To protect against this, either fuses or an additional power switch are used.

As in the previous case, energy first builds up in the inductor while the power switch is on. When the switch turns off, the current in the inductor reverses direction and, added to the battery voltage, flows to the output through the diode.
The output voltage of this circuit cannot be lower than the input voltage minus the voltage drop across the diode.
The input current is higher than the output current (sometimes significantly).


The third topology is used fairly rarely, but it would be wrong not to cover it.
This circuit produces an output voltage with the opposite polarity to the input.
It is called an inverting converter.
In principle, this circuit can step the voltage up or down relative to the input, but because of its topology, it is more often used only when the output voltage is greater than or equal to the input voltage.
One advantage of this topology is that the output voltage can be switched off by turning off the power switch. The first topology can do this too.
As in the previous circuits, energy is stored in the inductor, then delivered to the load through a reverse-biased diode when the power switch turns off.


When I was planning this review, I wasn't sure what would make a good example.
I could have built a step-down converter for PoE or a step-up converter to power an LED, but somehow neither idea seemed interesting, and both sounded pretty boring.
Then, a few days ago, a friend called and asked me to help him solve a little problem.
He needed a regulated output voltage, regardless of whether the input voltage was higher or lower than the output.
In other words, he needed a step-up/step-down converter.
The topology used by these converters is called SEPIC (Single-ended primary-inductor converter).
Here are a couple more good documents on this topology. 1, 2.
The circuit for this type of converter is noticeably more complex and includes an additional capacitor and inductor.



Now that I have a digital oscilloscope, I decided to capture some waveforms.

Of course, this is just a toy; the converter's power output is laughably low, though it is useful.



Related links.
7–14 V / 9 V, 0.5 A step-up/step-down DC-DC converter
MC34063 SEPIC
LED current regulator using the MC34063 IC
MC34063A description and connection diagram.
MC34063 DC-DC calculator

PCB file, schematic, datasheet. — link.

So, that's how this spontaneous mini-review of the IC turned out.

Summary.
These ICs are perfectly decent and worked for me, especially at this price.

I hope this review is useful. If you have any ideas for improvements, I'd be glad to hear them.
I'm sure I made a mistake somewhere, since I wrote this without notes, so please don't be too hard on me if you spot any errors.