Designing tool for MC34063A DC-DC converter - Page 1
Forum section: electronics / projects

author: truhlik_fredy
author_rank: Regular Contributor
timestamp: March 30, 2011, 07:19:10 pm
content: I tried to search forum if it's already here and still I'm not 100% sure if it's somewhere posted, but I will post it anyway. I looked back on couple older EEVBLOG episodes and one of them was DC-DC tutorial and it started me thinking, there must be some tool already to make easier for you design the 34063, so I started searching and found this:http://www.nomad.ee/micros/mc34063a/Perhaps somebody will find it handy.

author: Simon
author_rank: Unknown
timestamp: March 30, 2011, 08:59:35 pm
content: interesting, but I'd not rely 100% on it - useful for making comparisons though. You still have to bear in mind the chip limits. For example it lets me put in a 16V in and a 14V out but lets me set a frequency of 10 KHz. As we know this is not possible due to the constraints of the on/off times based on Ct. The higher the on time (or rather the lower the off time) the smaller Ct must be pushing up the minimum frequency, in my case 100KHz just does it

author: truhlik_fredy
author_rank: Regular Contributor
timestamp: March 30, 2011, 11:58:09 pm
content: It's just simple javascript. The upside is that you can easily have off-line version from it and it looks like simple enough that could run even on old PDAs.Code:tontoff=(vout+vf)/(vin-vsat-vout);sumtontoff=1/fmin;toff=sumtontoff/(tontoff+1);ton=sumtontoff-toff;// calculate componentsct=(4.0*0.00001*ton)*1000000000000;ipk=2*iout;if (ipk*1000>1500)alert("Switch peak current "+Math.floor(ipk*1000)+"mA exceeds 1500mA limit!");rsc=0.3/ipk;lmin=(((vin-vsat-vout)/ipk)*ton)*1000000;co=((ipk*sumtontoff)/(8*vripple))*1000000;document.forms["input"].elements["result"].value="Ct="+Math.round(ct)+" pF\n"+"Ipk="+Math.round(ipk*1000)+" mA\n"+"Rsc="+Math.round(rsc*1000)/1000+" Ohm\n"+"Lmin="+Math.round(lmin)+" uH\n"+"Co="+Math.round(co)+" uF\n"+"R1="+r1+"k R2="+r2+"k ("+Math.round(avo*100.0)/100.0+"V)";In the step down code is just current condition and rest is just math. But if you want and explain me more I could alter the code and add more checks.

author: Simon
author_rank: Unknown
timestamp: March 31, 2011, 06:02:10 am
content: yes that's interesting, well really you need to fully read and understand the datasheet including graphs taking note of all limitations. Adding options for an external switch trnasistor would be nice too, like a tick box to say your using an external transistor so that it dosen't flag a warning over 1.5A and you can put in your own saturated voltage figure for the transistor, that way the results will be more acurate and true

author: FxDev
author_rank: Regular Contributor
timestamp: April 03, 2011, 01:51:24 pm
content: 3-4 days ago I tested MC34063A for my Grid Connected DC/AC inverter. I don't like this shit! Its datasheet says I can take 1.5A but I didnt. Of course its efficiency is good but here the results.Test circuit elements: L=220uH, Co=2200uFResult ("verim" means effc., "yük" means load)But then I tested LM2576-5V! It gives what i want.Test circuit elements: L=150uH, Co=2200uFAnd the result:

author: Simon
author_rank: Unknown
timestamp: April 03, 2011, 04:27:53 pm
content: 1.5A is the peak voltage the internal transistor can take, usually this is twice the amperage you are working with. I'd not use that chip with an external switch for more than 500mA. Sure at low wattages you may not get good efficiency

author: Zero999
author_rank: Super Contributor
timestamp: April 03, 2011, 04:52:21 pm
content: Quote from: Simon on April 03, 2011, 04:27:53 pmCorrected.

author: Simon
author_rank: Unknown
timestamp: April 03, 2011, 05:02:13 pm
content: oops, yea I'm feeling a bit lousy this afternoon