step-up or boost with MC34063 - Page 1
Forum section: electronics / beginners

author: gbg
author_rank: Newbie
timestamp: February 23, 2019, 08:26:25 pm
content: How use MC34063 to boost a 3.7v/2200mAh battery to 12v or 9v and 700mA?Thanks

author: Ian.M
author_rank: Super Contributor
timestamp: February 23, 2019, 08:52:11 pm
content: Don't! Choose a different IC, designed specifically to boost from a single cell LiPO.700mA @ 12V is 8.4W, which will require more than 2.8A input current at the battery's end of discharge voltage, far more than a MC34063 can handle without an external switching transistor. Although the MC34063A can theoretically work down to 3V, its horribly inefficient at low voltages and wont provide enough gate drive to switch an external MOSFET effectively with under 4V supply. It also doesn't have any protection against over-discharging your battery.

author: ogden
author_rank: Super Contributor
timestamp: February 23, 2019, 08:56:40 pm
content: Quote from: gbg on February 23, 2019, 08:26:25 pmBy reading datasheet. First you have to understand how low power 200mA booster works, what defines it's output voltage (hint: Figure 9. Step−Up Converter). After you are familiar with IC, you may improve it with external switch (hint: Figure 10. External Current Boost Connections for IC Peak Greater than 1.5 A).

author: gbg
author_rank: Newbie
timestamp: February 23, 2019, 09:02:49 pm
content: Quote from: Ian.M on February 23, 2019, 08:52:11 pmis LM2577 good for me?

author: gbg
author_rank: Newbie
timestamp: February 23, 2019, 09:06:23 pm
content: Quote from: ogden on February 23, 2019, 08:56:40 pmis this work?https://cdn.instructables.com/FPM/CQPR/HV0KZ00Z/FPMCQPRHV0KZ00Z.LARGE.jpg

author: ogden
author_rank: Super Contributor
timestamp: February 23, 2019, 09:11:01 pm
content: Quote from: gbg on February 23, 2019, 09:06:23 pmDunno. I agree to @Ian.M that you shall not use MC34063 to boost 3.7v/2200mAh battery. I did miss to check battery/IC voltage ranges. As already mentioned - they do not match.

author: gbg
author_rank: Newbie
timestamp: February 23, 2019, 09:45:55 pm
content: Quote from: ogden on February 23, 2019, 09:11:01 pmOkBut how can i do?

author: ogden
author_rank: Super Contributor
timestamp: February 23, 2019, 09:54:53 pm
content: Quote from: gbg on February 23, 2019, 09:45:55 pmResearch, read manufacturer documentation. Try this for example:https://webench.ti.com/power-designer/switching-regulatorWhen you have something in mind - come back, ask question like "is this ok", not "how can I do".

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2019, 10:32:25 pm
content: Relevant:https://imgur.com/gallery/M1S0DbII don't have many numbers handy for battery operation, but MIC2619 comes to mind.Tim

author: Rick Law
author_rank: Super Contributor
timestamp: February 24, 2019, 01:49:52 am
content: Quote from: gbg on February 23, 2019, 09:02:49 pmRe: is LM2577 good for me?I have some emergence lights at 12V running on car battery. When used in "mobile" mode, I powered them with 12V from LM2577 (plus 18650 LiIon cell) instead of lugging a car battery around.Mine is at 700mA normal and super-bright tops at around 1.2A. Having used that for a few years, I would say it sure works but not efficient at all. Physics just gets in the way. I wont go into the detail that "power is proportional to square of the current" and all that. If you are interested in those details, post another reply here and we can dig into those nitty-griddy details.Here is the net-net. It would be optimistic to target 65% efficiency. Beside the efficiency issue, the high current draw results in high voltage drop. To boost 3.7V to get the same wattage as 12V@1A (Using 1A for easy math here), you would need 12/3.7 Amp = 3.24Amp.For 700mA, that is 3.24*0.7 =2.27Amp.For a single 18650, pushing out 2+ Amps would result in a rather high voltage drop rather quickly. The more the voltage drop, the more amperage it needs which of course worsen the problem more. Sooner than you can imagine, the 18650 drops to the 2.6V cut off. So the two problems in combination, the 3000mAH would have battery life that feels like a 1000mAH. You need to parallel a couple (or more) 18650 just to spread out the current draw to reduce the voltage drop.I still use those emergency lamps I put together with single 18650+boost. It gives me a better light spread than a single Cree T6+18650 and I prefer that good brightness-spread when cooking or washing up. For other tasks that narrow beam will do, I go with the single T6+1x18650. The boost (with heat sink) works and works well - but from an efficiency stand point, it is a looser.EDIT:I should add this: While I have used those boost for a long time, but time-ON is short. Each use is about 10-15 minutes to do cooking/washing. I don't want to leave the impression that I ran it "stay ON from full charge to full discharge" often. Heat as well as current draw are problems. So very quickly, I switch my my "regular" to "low" to extend the battery life. If you run it 700mA-ON-till-full-discharge, you may find it less acceptable than I do.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 24, 2019, 03:11:02 am
content: Quote from: gbg on February 23, 2019, 09:45:55 pmthere is no indication minimum voltage to the 34063 power pin, so i assume 3.7V is large enough. here's how (attached) from the datasheet...

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2019, 09:34:32 am
content: The problem with 2.png at low input voltages is the internal and external transistors form a Darlington pair and its Vce_sat at several amps Ic will be about a volt, which will push the already less than spectacular efficiency even lower, I estimate to around 50%. The resulting increase in input current, depressing Vbatt, to attempt to maintain 700mA @ 12V out, may even push it past the point where its efficiency decreases fast enough with decreasing Vin and its output voltage collapses.If you are forced to use a MC34063 for this application, you *NEED* a 2S series LiPO battery to maintain an adequate input voltage and reduce the current, and also a low Vgs threshold MOSFET for the external switching transistor to minimise the losses there.

author: Refrigerator
author_rank: Super Contributor
timestamp: February 24, 2019, 10:06:50 am
content: You don't necessarily have to use an IC. Some time ago I designed a two transistor boost converter to boost specifically from a single cell lithium battery.R2 is not needed and to increase the voltage you just change out the zener diode. I've used this circuit to boost from 5.5V all the way to 400V (with suitable mosfets of course), including 9V and 12V.The limit of my design is about 17W so you should be able to get at least 1A at 12V with efficiency of at least 85%, the circuit idles at about 50mA (with an output LED)Also note that the circuit does not have a low voltage cutoff so make sure your lithium cell has a protection circuit.

author: gbg
author_rank: Newbie
timestamp: February 24, 2019, 05:21:12 pm
content: Quote from: Refrigerator on February 24, 2019, 10:06:50 amI have a low voltage cutoff (dw01a)What is amper of L1?I can not find BSZ0920NS.

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2019, 06:06:39 pm
content: Assuming Refrigerator's 85% efficiency figure is good, the average input current for 700mA @12V out would be 3.3A @3V - a reasonable cutoff voltage for a LiPO. The on time must be three times the off time as there's 3V across L1 during the on time and 9V the other way during the off time, so the average during the on time is 4.4A. The inductor current ramps up linearly during the on time (assuming Rds_on and R(L1) are insignificant compared to the inductance) so you need a peak current without saturation of double the average, so 8.8A. You'll need a bit of safety margin on top of that.That's really pushing the limits for a 2200mAH high discharge current LiPO without protection, so you'll need a lot of low ESR bulk decoupling capacitance at the boost circuit input to have any chance of avoiding tripping the battery protection.

author: gbg
author_rank: Newbie
timestamp: February 25, 2019, 06:16:03 am
content: I simulate this but don`t work

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2019, 01:38:49 pm
content: C1 330p, not 33p.FYI, if you're looking for an out-of-the-box solution that doesn't require adjustment, this is not it.There are more reliable, discrete circuits possible, but they require more components and/or coupled inductors, and even more adjustment to create, if not necessarily to fit to a given end use.Stick with commercial boost regulators and follow the application notes.Tim

author: gbg
author_rank: Newbie
timestamp: February 25, 2019, 04:59:00 pm
content: OPSI create new but not work

author: ogden
author_rank: Super Contributor
timestamp: February 25, 2019, 05:16:15 pm
content: Quote from: gbg on February 25, 2019, 04:59:00 pmThen drop it. If you can't run it in simulation using ideal components, then in real life it will not work for sure.

author: Refrigerator
author_rank: Super Contributor
timestamp: February 27, 2019, 04:54:22 pm
content: Quote from: gbg on February 24, 2019, 05:21:12 pmAny mosfet with a low enough Vgs should work, IRF44 will not work because Vgs is too high.I personally use mosfets from motherboards.Quote from: gbg on February 25, 2019, 04:59:00 pmI ran the simulation myself and sure enough it doesn't work with an IRLZ44N but any other switching mosfet does work.PS: the circuit originally used a 2N3904 but i modified this one to work with a 2n2222.Also if you don't have LTspice already, please get it because it's awesome (and free).