I have been using the MC34063A whenever I need a SMPS, but I've heard that they are old and inefficint. I've noticed that they can't put out too much current without heating up and starting to smell a bit (starts to smell at 500 ma even though it's rated at 750 ma). Because of this, I've decided to get some new SMPS ICs. I just wanted to know what adjustable SMPS ICs people suggest as a replacement. Thanks.

 

There's nothing horribly bad or inefficient about the MC34063A. Heat and smell are subjective. The important thing is that you don't exceed the maximum junction temperature allowed for the chip.

Any current/heat issues with that regulator are typically addressed by using an external pass transistor; properly heatsinked.

 

Also, a self-made heat sink can be attached to the chip. This will reduce the heating of the chip.

 

Hello,

What package version of the MC34063 are you using?



You could use some stick-on heatsinks as @Bordodynov suggested.
Here are some examples of them on ebay:
https://www.ebay.com/itm/8-Pieces-C...m=122442944882&_trksid=p2045573.c100507.m3226

Bertus

 

What diode(s) are you using?

That IC is a an old design based on an even older Fairchild part. It will be somewhat less efficient than new designs with integrated switches because it uses a bipolar transistor instead of a FET.

Its mode of regulation is very different from most switcher controllers. It is a "hysteritic" controller that regulates the ripple voltage on the filter capacitor. This relieves the need for careful analysis of the loop frequency response and design of frequency compensation for an error amp.

 

its just a simple BJT integrated switcher never meant to be for large currents and has been along for quite a while

LM2596 has better efficiency XL4005 is MOSFET I think.
For these normally youd use a decent flyback diode (a fast rectifier or a schottky).
You need modern capacitors too old parts may have quite high ESR.

The Motorola IC I think has fixed pulse ratio, BJT as mentioned, and the frequency can be off a bit what it should be, as well I saw it doesnt have much of an effect. And yes the part gets hot more sooner than you expect. Youd need superiour parts and still would see limited efficiency.

So normally only use this for small current otherwise the LM2596 or XL4005

Its a science on its own and theres ICs such as TL494 (also quite old) giving you far more options but also you need quite a few components. Most recent ICs have efficiencies above 90% and use small inductivity as well high frequency but it comes with a set of problems, you need parts capable of handling a MHz or two or youd see the noise travelling on the wires and if theres something wrong they tend to just pop up and glow for a moment and that was it then.

 

I have the PDIP package. Apart from a zener diode going from pin 2 to ground (inductive spike protection I assume) I'm not using any diodes. I'm going off the schematics included in the datasheet. I guess I can try using an external transistor next time I have issues with the chip heating up.

 

Zener from pin 2 to ground? Inductive spike protection?

No. That diode is an integral part of the switcher circuit and must be a schottky or fast recovery pn junction diode.

 

I have the PDIP package. Apart from a zener diode going from pin 2 to ground (inductive spike protection I assume) I'm not using any diodes. I'm going off the schematics included in the datasheet. I guess I can try using an external transistor next time I have issues with the chip heating up.

Try the Viper series of chips,

http://www.st.com/en/power-management/viper.html?querycriteria=productId=SS1835

or the Uc3845 series of 8pin dil.

 

I have the PDIP package. Apart from a zener diode going from pin 2 to ground (inductive spike protection I assume) I'm not using any diodes. I'm going off the schematics included in the datasheet. I guess I can try using an external transistor next time I have issues with the chip heating up.

Looks like there is a problem, the IC doesnt use Zener diode.

 

*facepalm* Well aren't I a doof. Not sure why I thought the schottky was a zener. Thanks for pointing it out otherwise I probably wouldn't have noticed.