Why the MC34063A is used so much to power microcontrollers?

Thread Starter

dbagnis

Joined Dec 15, 2021
1
This issue has worried me for a long time. I don't understand why the MC34063A is used in motor scooters, wheelchairs, hoverboards, etc. to power sensors and digital parts. Why not use linear regulators? Is it due to the electrical noise of the Brushless motors?
 

Papabravo

Joined Feb 24, 2006
18,778
Linear regulators are inefficient and may dissipate large amounts of power if the difference between the input and output voltage is more than a couple of volts.
 

InTheSky

Joined Sep 28, 2018
2
As said above, heat and power dissipation/loss are the chief reasons to opt for a switching power supply. The mc34063 may not be the most efficient on the block but its cheap, easily available everywhere, highly configurable as a buck/boost/inverting controller and with a switching freq of 100khz max, easily "quietened" by a front-end filter.
 

DickCappels

Joined Aug 21, 2008
8,804
To add to that: ...and by their very nature there is no reason to worry about transient response beyond assuring that the output capacitor is large enough. It is ok for the loop to oscillate - that's how it works!
 

Ian0

Joined Aug 7, 2020
5,481
Each to his own. I can’t understand it myself, I think it belongs in the same “consigned to history” bin as the 741. It’s just rehashed 78S40, with a slow lossy output stage and a noisy control loop. There are so many good little switched mode ICs out there. Let the 78S40 (and its offspring) rest in peace.
 
Last edited:

atferrari

Joined Jan 6, 2004
4,630
After reading the detailed note of application that came with it and the 78S40 IIRC, I started to dream building a switcher just for the pleasure of making some experience but reading comments as above discouraged me every time.

No more modern gem comes with such a complete guide to attempt at least once.

The Timex Sinclair 268 of such a short life, came with one 78S40.
 

mikewax

Joined Apr 11, 2016
184
the scooters i've seen have a switcher with one bootstrap output to provide voltage to drive the Nfets and one intermediate voltage output that goes to a 7805 or an 1117 to power the brain and sensors. battery voltage is higher than the maximum input voltage of a 7805
 

GetDeviceInfo

Joined Jun 7, 2009
2,100
This issue has worried me for a long time. I don't understand why the MC34063A is used in motor scooters, wheelchairs, hoverboards, etc. to power sensors and digital parts. Why not use linear regulators? Is it due to the electrical noise of the Brushless motors?
you indicate battery operated devices. Efficiency becomes a higher priority and switching wins.
 

MrAl

Joined Jun 17, 2014
9,148
This issue has worried me for a long time. I don't understand why the MC34063A is used in motor scooters, wheelchairs, hoverboards, etc. to power sensors and digital parts. Why not use linear regulators? Is it due to the electrical noise of the Brushless motors?
Hello there,

Already a lot of good posts before mine so i may repeat something already mentioned but i'll be brief.

First, there are a number of designs that are simply not changed because they have been working well in the past with no problems. Second, the chip is a low cost solution for a switching converter. Third, the circuit is quite simple and offers some overload protection without the hassle of adding extra circuitry.
So there are three or four pro's right there.

The reason for NOT using a linear has already been mentioned, but just to be clear, there are some applications where a linear regulator is actually more efficient than a switcher, but only when the input and output voltage are nearly the same already. Thus in most cases a switching power supply is the choice.

Now as mentioned by Ian already, there are drawbacks to using this chip in a general purpose switching regulator circuit. First, it is an older device and so it is not designed for high efficiency and small component footprint as more modern chips would be. In fact, if you do a few calculations you will find that the inductor required to keep the output ripple current and voltage to within some limit, it will always require a larger inductor than circuits with more modern chips, and that is because the output frequency spectrum is all over the place, unlike constant frequency converter chips. In particular, the lower frequency components that appear at the output simply because of the method of regulation used by this chip. You will note howeve, that this doesnt affect motor drive circuits as much as actual power supplies that have to put out a clean output, so that is probably why they are used in motor control circuits you talked about. Might not even need an inductor for those applications, and thus the con of needed a larger than usual inductor becomes moot while all the pro's work in favor of the design.

So there you have it, the most important design considerations and how this chip fits in.
If i remember right, i think they were also used in floppy drives for computers.

Just to recap...
Pro's: proven reliable device, low cost, simple circuit, some overload protection, ok for motor drives.
Con's: wide output frequency spectrum means a larger inductor required for guaranteed smooth output applications.
 
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