First circuit not working - boost converter - Page 1
Forum section: electronics / beginners

author: de_light
author_rank: Regular Contributor
timestamp: January 14, 2021, 01:26:38 pm
content: Trying to get my first circuit working. I've tried to design a simple boost converter based around the MC34063A IC. I don't really have a use for this - it is just a 'proof of concept' and wanting to try something to get working on veroboard.Problem is: it doesn't work.I can input a voltage into the circuit and all I get out of it is roughly what I put in, barring a small voltage drop due to about 200 Ohms resistance (Say I put 10VDC in, I get about 9.64VDC out).I've tried to follow the example schematic on the MC34064A datasheet, page 5, for a boost converter but clearly doing something wrong.https://www.onsemi.com/pub/Collateral/MC34063A-D.PDFI'm using a 250kOhm potentiometer as I don't have anything close to a 47k resistor in my box - I understand that you can use it as a rheostat by just connecting the wiper and another pin, so that is what I have tried to do.Please forgive the cackhanded soldering, as I said, first time at this!

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 14, 2021, 01:58:14 pm
content: Quote from: de_light on January 14, 2021, 01:26:38 pmno you are not. you are using gigantic 230mH inductor, maybe thats too much, in example is using 170uH. please observe and study formulas in page 11.. i think switching freq for MC34064A cant be too low, ymmv.

author: de_light
author_rank: Regular Contributor
timestamp: January 14, 2021, 03:03:59 pm
content: Thanks for your reply. It was all I had lying around.Could you explain to me, as a beginner, why the circuit might not work if the inductor is too large? As in, why no switching action at all is happening?

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 14, 2021, 03:28:00 pm
content: big inductor will have slow current rise, when switch on stage is timed out, there is not enough current to reach set boosted voltage, and then smps controller will detect this very slow rising up at output voltage it may think a heavy load on the output and shut itself down for protection, this happened at least to other smps IC that i used. havent fail a MC34064A though to such condition, but it could be what has happened to you. i cant explain it any better or with academic and formulas, i just talk out of some experience. my suggestion is reduce the inductance and follow the example to the values, when it works, slowly increase the value(s), you should see some difference in switching behaviour (frequency, duty cycle etc) until it fails again. ymmv.edit: and using trimpot on feedback voltage is quite not advisable, output ripple will be less optimized. if you dont have good reason as to why you use it (adjustable output is one reason) just use fixed value resistor, ymmv.

author: de_light
author_rank: Regular Contributor
timestamp: January 15, 2021, 12:45:34 am
content: My apologies. I pulled the inductor and measured it with a component tester - it is actually 220uH.So that's that out of the equation!Reworked schematic:

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 15, 2021, 05:48:14 am
content: what is Vcc, what is set Vload? what is set R3? make sure no short at bottom side of the board, i can see some solder blob.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 15, 2021, 08:03:47 am
content: Suggestions:1. Start over.2. Redraw the schematic to make it easier to layout physically on the perfboard. Power input on the left, positive power rail on top, negative (ground) rail on bottom, output (load) connection on the right, chip in the middle, etc. Try to make your physical layout with as few crossovers as possible to eliminate possible shorts. This starts with careful layout on paper following the general guidelines above. (or dreaming while trying to fall asleep...) It's not really possible to tell from your photos whether or not you have circuit errors, shorts, cold solder joints, etc. A better layout would help in this regard, as well as making it easier actually to build the thing.3. Use a socket for the chip. This will eliminate the possibility of burning the chip while practicing soldering. And other reasons too-- you will eventually want to swap a questionable chip for a known good one and sockets make this job a heck of a lot easier.4. If you don't have exact or close values for resistors or capacitors, you can build up the desired values using parallel-series combos of other values. Don't just grab a trimpot until you have a working circuit with a fixed value resistance.5. For this kind of work use tin-lead solder, not lead-free.6. For fine uninsulated wire connections, strip some stranded hookup wire and use individual strands. Got an old PC power supply you can scavenge for wire? For insulated wire connections you can slip tubes of stripped insulation back over the little individual strands. It's a lot easier than using enamel coated magnet wire.BTW it looks to me that one of your resistors is burned.Good luck! (Don't feel bad, you should see some of my first builds. No--wait--- you shouldn't.....)For example look at the way this schematic is drawn. It's the same basic circuit, but drawn according to the conventions I outlined above. It has no crossover wiring and if this layout is followed on the perfboard no shorts will be possible. Also the chip pins are shown in the natural order as they appear on the actual chip, not all mixed around to make some autorouting possible. Believe me, this makes it much easier to build and troubleshoot, as opposed to trying to use a schematic where, say, pins 3 and 8 are drawn next to each other and pins 1 and 2 are on opposite sides of the drawing.https://i.pinimg.com/originals/3f/8a/38/3f8a38b64a60ec86512da83afa9238e0.png

author: ledtester
author_rank: Super Contributor
timestamp: January 15, 2021, 09:01:15 am
content: This article suggests you can get a circuit working on a breadboard:http://www.learningaboutelectronics.com/Articles/Switch-mode-power-supply-circuit-with-an-MC34063.phpMight be worth trying just to see if you can get it to somewhat work.And this thread suggests that breadboarding a buck converter (with some care) is very doable:https://www.eevblog.com/forum/projects/mc34063-help/

author: ledtester
author_rank: Super Contributor
timestamp: January 15, 2021, 09:37:03 am
content: Just to test your MC34063, you might try this test circuit:https://www.eevblog.com/forum/beginners/why-does-mc34063-switch-behave-so/msg3413386/#msg3413386

author: de_light
author_rank: Regular Contributor
timestamp: January 18, 2021, 11:19:34 am
content: Just like to say thanks. I have managed to get this working to convert 2.5VDC to 5V regulated. I started from scratch and recalculated all my values.I think my values used or my wiring in the initial build were completely wrong - it seemed like the MC34063 never 'turned on'. Now all good - huge success for me even with this tiny project - something I have wanted to do for ages!