Least Expensive Circuit to double voltage 5VDC @ 2A to 10VDC @ 1A - Page 1
Forum section: electronics / beginners

author: mribble
author_rank: Regular Contributor
timestamp: September 03, 2020, 05:35:14 pm
content: I understand the basic principle of PWM the DC voltage to and then using 2 stages of capacitors to double the voltage as explained here:https://www.electroschematics.com/555-voltage-doubler/However, I'm hoping the experts here can suggest a circuit that is lower cost since I am planning to make a few thousand PCBs with this on them. If there is some IC that lowers part count or some common components that experts would typically use for this I'd greatly appreciate any suggestions.Thanks for any help!

author: Ian.M
author_rank: Super Contributor
timestamp: September 03, 2020, 05:56:05 pm
content: QuoteCant be done, as its impossible to boost the voltage with 100% efficiency. If you had 5V @2.1A, or could settle for 10V @ 0.95A (i.e 95%) efficiency, it would be doable but hard. As the required efficiency drops it gets much easier and below about 80% becomes trivial, and there are more suitable boost converter ICs or boost converter controller ICs than you can shake a stick at.

author: mribble
author_rank: Regular Contributor
timestamp: September 03, 2020, 06:03:48 pm
content: Thanks for the feedback. I understand 100% efficiency is impossible I would be fine with 80%+ and happy with 90%+.I know there are thousands of boost converters on Mouser, but doing a parametric search there is hard because many require different external parts, which greatly impacts my most important factor which is price. I was hoping someone here could point me at a best practice for low cost voltage doubling in this voltage and current range.I'm not sensitive to a small amount of voltage ripple since that might be another question you folks ask.

author: ledtester
author_rank: Super Contributor
timestamp: September 03, 2020, 06:18:25 pm
content: QuoteOn Mouser you'll find those chips under the "switching voltage regulators" category:https://www.mouser.com/Search/Refine?N=10368713You will still need some external parts, though -- typically an inductor, a mosfet as diode as well as some passives. But a big advantage over the 555 design is that you'll get regulated output.This video goes over what a typical boost converter circuit will look like and what kind of performance you can expect:https://youtu.be/jYMGCLsytT4The XL6009 datasheet also shows what a typical circuit would look like for any of these switching voltage regulators:https://www.nikom.biz/pdf/XL6009.pdf

author: Clear as mud
author_rank: Regular Contributor
timestamp: September 03, 2020, 06:20:01 pm
content: I think the cheapest is the switched-capacitor voltage doubler, but it's efficiency will be lower than a comparable boost converter using actual inductors. Also, its actual voltage output will be somewhat lower than double the input voltage (and will not be regulated very well, as mentioned in another reply).If you want to get parts cost as low as possible, I believe you would want to use old-fashioned BJT transistors for switching, and design using discrete components. Using additional transistors if necessary, make an oscillator to drive the switching transistors.I have not actually done a design like this, but I've seen discrete transistors used inside cheap mass-produced switching supplies.

author: Ian.M
author_rank: Super Contributor
timestamp: September 03, 2020, 07:08:46 pm
content: Lets consider the theory from first principles:Neglecting losses, the inductor current builds up linearly storing energy in it for the on time which for a voltage doubling boost converter is ideally 66.7% of the period. It then cuts off and the inductor current decays linearly as it dumps that stored energy into the output capacitor. The peak current is therefore double the average current during the on time or off time and to deliver a continuous 1A out, with only 33.3% of the period to deliver the energy, means you've got to multiply by another factor of three to get the peak switch current then apply whatever fudge factor you need for losses and derating. You are therefore looking for apeak switch current capability in excess of 6A.(There are ways of fudging that, e.g. by not letting the current drop to zero before switching the inductor's swinging end to ground to dump more energy into it, but that reduces the effective energy storage of the inductor so what you gain on reduced peak current you typically loose on cost of magnetics and controller complexity.)Also note that switching frequency directly impacts the size and thus cost of the capacitors and inductors required, so within reason, the higher the better. An integral synchronous rectifier is only a moderate benefit because its only worth up to 5% better efficiency at your output voltage. They are far more important at lower voltages and higher currents as diode Vf*If become the dominant losses.Put in appropriate search criteria, sort by price, and you can work through from the low end viewing their datasheets and quickly rejecting those that obviously cant meet your requirements. I did a quick and dirty job on the limits and got about 60 candidates. It then took me no more than a minute to reject the first four based on the first page of their datasheet. Note whether they require an external diode for any you don't reject.I reckon, ignoring price, you'll be able to get it down to around ten or so in no more than an hour. Then take the lowest and highest frequency ones remaining, and work out the cost of the required inductor and capacitor properly. Download the search results as a spreadsheet, flag the ones that *CAN* do the job, and in another column, if they need a diode, and interpolate a cost for the passives vs frequency from the two extremes so you can calculate a total cost for each of the validated candidates. Pick the cheapest total cost and work out its passives cost, and diode cost if any in a separate column, use the figures to refine the cost vs frequency interpolation for the others, rinse and repeat till you've got the three cheapest candidates.IMHO there's about three hours work there to narrow it down. Further distributors with a decent parametric search with a download results option will be less work as you can use the reject list of parts that cant do the job you've accumulated so far to automatically eliminate them from the downloaded new results, and for anything in your qualified candidates list you only have to update the pricing and see if it shifts it into being a candidate for the cheapest three overall, so you only have to do the full costing exercise for any new candidates that cant immediately be ruled out on chip cost alone.Dropping back to 'Clear's suggestion of an entirely discrete design - well, without custom magnetics and a fairly complex control circuit, efficiency will *SUCK*, and its a major design exercise to even get over 80%. Evaluating and optimizing even a single candidate design properly is likely to cost more than you can afford spread over so few units in the production run. (I estimate, ballpark, around $0.75 per design per unit over 3K units, with a subject expert on hand, far more if you are learning on the job and billing it to the project.) If you were planning to build several million or better several tens of millions it would be a different matter,

author: mribble
author_rank: Regular Contributor
timestamp: September 03, 2020, 08:45:43 pm
content: I totally agree that the discrete solution probably isn't for me as designing that would be really hard for my skill level.I will try to follow your suggestions for a parametric search. I think you might be estimating based on your skill level and not mine though. I expect it will take me a much longer time than you estimated, but I will go that route since it does sound like this isn't something that is common enough that people here can just quickly suggest something. I certainly don't expect people to do all the work for me and now that I know there isn't a quick answer I'll look into it. Thanks again!

author: Ian.M
author_rank: Super Contributor
timestamp: September 03, 2020, 08:57:32 pm
content: It really doesn't take much nous to quickly reject parts where the bold bullet point features on the first page of the datasheet give an inadequate input or output voltage range, or inadequate peak switch or average output currents. Those are't specs, they are the most optimistic claims the engineers will let the marketing department get away with so if they are insufficient there's no point in reading further. The bulk of the time per datasheet was clicking the right link and waiting for the page to load, not reading and digesting the contents.

author: BrianHG
author_rank: Super Contributor
timestamp: September 03, 2020, 09:12:13 pm
content: https://www.ti.com/product/LM2587Already assembled here:https://www.aliexpress.com/item/32829782538.html?spm=a2g0o.productlist.0.0.54274b34QMa1lK&algo_pvid=41ef492e-308d-44db-a19b-3cfe465ee5d5&algo_expid=41ef492e-308d-44db-a19b-3cfe465ee5d5-2&btsid=0bb0622c15991668270876564e8f32&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_Use the 5v-12v unit and adjust the output voltage down to 10v with the onboard trimpot.This one is less beefy, but better efficiency. (36cents each assembled) (I don't trust the claim of 2 amps, see IC datasheet below)https://www.aliexpress.com/item/4000283637347.html?spm=a2g0o.productlist.0.0.54274b34QMa1lK&algo_pvid=41ef492e-308d-44db-a19b-3cfe465ee5d5&algo_expid=41ef492e-308d-44db-a19b-3cfe465ee5d5-5&btsid=0bb0622c15991668270876564e8f32&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_Datasheet for smaller board #2:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi1s63Kjs7rAhVzg3IEHduqB_cQFjABegQIBBAB&url=https%3A%2F%2Fprom-electric.ru%2Fmedia%2FMT3608.pdf&usg=AOvVaw3IWlc8eb24QE65ecfDKuhzWith this one, expect >90% efficiency when converting 5v to 10v if you have a good inductor.

author: BrianHG
author_rank: Super Contributor
timestamp: September 04, 2020, 12:27:46 am
content: Unlike the 36cent solution I listed above, here is the cheapest from Digikey.However, the price is just the IC. It doesn't include PCB, inductor, diode, caps, resistors & connector terminals.https://www.digikey.com/en/products/detail/ricoh-electronic-devices-co-ltd/R1213K001B-TR/10244756According to the datasheet, you will get 950ma out @ 12v with 5v source, so, 1amp out when set to 10v output.However, the IC all by itself is 1.58$ USD.

author: ebclr
author_rank: Super Contributor
timestamp: September 04, 2020, 12:37:21 am
content: Will a dollar fit ?https://item.taobao.com/item.htm?spm=a230r.1.14.23.32612f5cnzIHkq&id=582230734611&ns=1&abbucket=7#detailOhhhhh you believe is expensive right ?https://item.taobao.com/item.htm?spm=a230r.1.14.208.14bd2d16RRAL4t&id=531647778768&ns=1&abbucket=7#detail

author: BrianHG
author_rank: Super Contributor
timestamp: September 04, 2020, 01:00:03 am
content: Quote from: ebclr on September 04, 2020, 12:37:21 amThose 2 are based on the MT3608, like the 36cent unit I listed above.In fact the second one is identical, but only 14cents USD. Before import taxes.Like I said, 1 amp at 10v is cutting it too close for the MT3608, but it may still work out for the OP.

author: ledtester
author_rank: Super Contributor
timestamp: September 04, 2020, 01:02:12 am
content: Those MT3608 modules are highly over-specced... they can't even do 9V in to 12V out at 2 A:https://youtu.be/LMKiPE_2Uu4?t=7m45s

author: BrianHG
author_rank: Super Contributor
timestamp: September 04, 2020, 01:11:43 am
content: Quote from: ledtester on September 04, 2020, 01:02:12 amThey are miss-specced by those selling the module not knowing how to interpret the data sheet. The data sheet says that the onchip mosfet is 2amps with a 4 amp switch current limit. The output current is a fraction the mosfet current when increasing the voltage.If those boards have a good inductor, they will only give the op around 850ma @ 10v, when he gives the IC 5V minimum. Output current will suffer greatly if the module is only getting 4.5v.This is why I listed the beefier module first, then I commented on the 2amp spec for the second module being false. Then I attached links to the datasheet of both module's IC's. Then in another post, I also offered Digikey's cheapest IC solution.The LM2587 board can deliver 1.2Amps @ 12v with a 4.5vdc input according to TI's datasheet. So when adjusted to 10v out, there will be even a bit more clearance if the OP only needs 1 amp. However, I do not see a heatsink on that PCB. The LM2587 from Aliexpress is the cheapest solution with a little headroom, though, I would recommend at least adding a little heat-sink glued to the top of the IC.

author: wraper
author_rank: Unknown
timestamp: September 04, 2020, 01:23:21 am
content: Quote from: Clear as mud on September 03, 2020, 06:20:01 pmDoubling at 2A curent? cheaper? It will be an expensive piece of crap. If you want to save money, find cheap Chinese boost converter IC, cheap inductor and so on. You can look at LCSC for that.

author: wraper
author_rank: Unknown
timestamp: September 04, 2020, 01:30:06 am
content: For examplehttps://lcsc.com/product-detail/DC-DC-Converters_SX-Shenzhen-Suosemi-Tech-SX1301LR-G1_C80206.htmlWith all surrounding components it will be around $ 0.25-$0.3 (excluding assembly and PCB cost).

author: mribble
author_rank: Regular Contributor
timestamp: September 04, 2020, 11:28:41 am
content: You guys suggesting looking for boost converters on Alibaba was a great idea. One thing I don't understand is how they sell the LM2587 module for under $2 when I can only find that part on Mouser for $5 even in 1000 quantities. I guess there must be some alternatives not from TI.The MT3608 is quite interesting. The specs I quoted here are actually quite safe. I'm going to read the datasheet and look at that testing video to see if my actual specs will work. I still need to finalize them, but they are close to 5 (from USB) to 9V @0.7A and I can probably get buy with less current if I put in a current protection feature or if the boost converter handles this gracefully. I need to double check a few things, but maybe I can make that chip work.I do have some contacts in China that can get me anything I ask for at a good price, but I often have a hard to knowing what to ask for so this pointer helps a lot.

author: wraper
author_rank: Unknown
timestamp: September 04, 2020, 11:37:36 am
content: Quote from: mribble on September 04, 2020, 11:28:41 ambecause they are fake crap

author: BrianHG
author_rank: Super Contributor
timestamp: September 04, 2020, 11:53:30 am
content: Quote from: mribble on September 04, 2020, 11:28:41 amThe RICOH Electronic Devices Co., LTD. chip I listed actually is well specked and better regulated than the Chinese MT3608. Mouser has them as low as 65cents in high quantity. Chip1Stop has them at 72cents for 1 and 57cents in quantity and you wont need to worry about that tiny un-heat-sinkable SOT23-5 MT3608. Their datasheet is also far more complete compared to the MT3608.