Design a tiny dc-dc converter for Gameboy Pocket - Page 1
Forum section: electronics / projects

author: EliotFR
author_rank: Newbie
timestamp: August 29, 2025, 10:25:59 am
content: Hi everyone,First of all, i'm a begineer.I have already made small PCBs but this one seems more complicated to me.I'm the happy owner of a Gameboy Pocket, but sadly, it won't turn on.After a fast inspection, the DC-DC converter named U5 is dead.From the 2 AAA batteries (VCC-3V ), it produce 5V on VDD ( 70-100mA average) and -18V on VEE.Idk how much draws the VEE, it only use to power the constrat adjustement, for the TN LCD bias generation, i guess it's under 10mA.U5 is a daughtercard :Front / Back :That's why, i want to produce a replacement pcb for U5, to repair my gameboyAfter a quick search, i havn't find any dual output boost converter which goes down to -18v ( TPS6513x goes up to -15v ).Knowing that I don't have many space, do you have any recommendations?Maybe I should use two dedicated ICs.Any advices ?Thanks a lot for your reading.Sorry is my english is a little poor / approximate

author: daisizhou
author_rank: Super Contributor
timestamp: August 29, 2025, 11:18:20 am
content: Why don't you try to repair it? Because there are only 6-7 transistors or MOS tubes on this boardIn my opinion, redesigning the PCB is not a simple matter. You need to consider many factors for low power consumption, such as ripple, noise...

author: EliotFR
author_rank: Newbie
timestamp: August 29, 2025, 11:40:40 am
content: On my board, the inductor is broken, and it's a custom inductor.I have no idea where I can get a new inductor with this specs ...And it must be exactly the right size to fit under the motherboard, like the :So I thought it would be easier to make a clone. But apparently not.After a quick look and the diagrams have already been reversed.Components for LSEP1088A1 PCB :Capacitors :C1: 4.7 uF, 1206C2: 1.5 uF, 1206C3: 100 nF, 0603C4: 1 nF, 0603C5: 1.5 uF, 1206C6: 100 nF, 0805C7: 22 nF, 0603C8: 100 nF, 0603C9: 150 pF, 0603Resistors :R1: 100 kOhm, 0603 ("104")R2: 22 kOhm, 0603 ("223")R3: 82 kOhm, 0603 ("823")R4: 47 kOhm, 0603 ("473")R5: 22 kOhm, 0603 ("223")R6: 2.2 kOhm, 0603 ("222")R7: 3.3 kOhm, 0603 ("332")R8: 1.8 kOhm, 0603 ("182")R9: 22 ohm, 0603 ("220")Diode :D1: Panasonic MA2J111, SOD-323 ("1B")D2: Panasonic MA2J111, SOD-323 ("1B")D3: Panasonic MA2J111, SOD-323 ("1B")D4: Panasonic MA3X748, Schottky 1=A 3=K, SOT-23 "M4A"D5: Panasoniz MAZ8047, 4.7V Zener, SOD-323 ("4-7")Transistors :Q1: Panasonic 2SD601A, NPN BEC, SOT-23 "Z R"Q2: Panasonic 2SD601A, NPN BEC, SOT-23 "Z R"Q3: Panasonic 2SD601A, NPN BEC, SOT-23 "Z R"Q4: Panasonic 2SD1119, NPN BCE, SOT-89 "T R"Q5: Panasonic 2SD601A, NPN BEC, SOT-23 "Z R"Inductors :T1: Custom transformer: 1-4 primary, 2-3 aux, 5-8 secondary, 6-7 secondaryWindings (top->down, left->right):4-1: 26 turns7-6: 91 turns8-5: 26 turns3-2: 26 turns1-4:0.75 ohm DCR28 uH @ 100 Hz2-3:0.40 ohm DCR31 uH @ 100 Hz5-8:0.67 ohm DCR28 uH @ 100 Hz6-7:1.66 ohm DCR378 uH @ 100 Hz

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 29, 2025, 11:49:15 am
content: In case the repair attempt doesn't work:It´s quite easy to add a charge pump voltage multiplier to a standard boost converter. If you invert the 5V-output of the boost converter and multiply it by 4, you should come quite close to -18V. You just need 4 capacitors and 4 diodes for this purpose.I don't quickly find an example schematics - but tell me if you need it.EDIT: In fact you need 8 caps and 8 diodes for this purpose - see the link in the post below.

author: EliotFR
author_rank: Newbie
timestamp: August 29, 2025, 11:59:24 am
content: I didn't know this kind of assembly, I will find out more, thank you very much.

author: langwadt
author_rank: Super Contributor
timestamp: August 29, 2025, 01:06:39 pm
content: https://www.analog.com/media/en/technical-documentation/data-sheets/1613fs.pdfbottom of page 10 is a start

author: daisizhou
author_rank: Super Contributor
timestamp: August 29, 2025, 10:53:41 pm
content: Quote from: langwadt on August 29, 2025, 01:06:39 pmI'm just curious, why do so many people like to use the LT solution?In my opinion, LT solutions are usually expensive and their performance is not as good as some Chinese manufacturers' solutions.I mean MT XL EG, even some of TI's solutions are sometimes better than LT's

author: Buriedcode
author_rank: Super Contributor
timestamp: August 29, 2025, 11:02:12 pm
content: Quote from: daisizhou on August 29, 2025, 10:53:41 pm"Better", at least in engieering is not only a relative term, but also requires a lot of context. If the only available part is an Analog part.. then surely thats "better"? Do you mean better in terms.. Iq, output ripple, switching frequency, EMI, regulation, startup behavoir, cost, size, availability...As for why its recommended.. maybe it was first on the google search results? Maybe they've used the part before and it did the job, which is one datapoint in its favour.If cost is an issue, I'm sure there are far cheaper alternatives. But using known manufacturers parts means you get good documentation (generally..), support, and reasonable confidence it does what it says. Lesser known manufacturers may well be just as good, but if one hasn't used them, before - they might not have the confidence in the part.Also, we all have our biasesI personally have something against Maxim and TI, but still use their parts.

author: Buriedcode
author_rank: Super Contributor
timestamp: August 29, 2025, 11:18:42 pm
content: To the OP:I don't own a gameboy pocket, but I think you're correct in assuming the LCD VEE won't require much current. Most I've seen was an old 320x240 STN that drew a whopping 8mA.For 5V to -18V, a charge pumpcouldwork, but there are some caveats. - By charge pump I mean either an inductor based boost converter with a couple of diodes and caps added to make a negative voltage from the switching node, OR.. a dedicated charge pump IC. (Max868?)Firstly, they are often not regulated. This isn't always a problem for LCD's since the VEE uspply draw tends to be pretty stable, so no variations in current draw = no variations in output voltage, but it does mean that the voltage will decrease (well, for a negative voltage, actually increase, towards -V) the more current you draw.Secondly, for currents >10mA the voltage sag tends to be quite severe.Thirdly, despite often sold as a"low EMI" solution (no inductor for detected charge pumps) they sitll have high current switching paths. But given the inductor in your original circuit doesn't seem to be shielded anyway, I doubt this will be an issue.And lastly, they can have a fair bit of ripple on the output - probably not a problem for an LCD supply, but anything remotely sensitive to output ripple generally requires a filter.But I'll secondPhil1977's andlangwadt's suggestion. A simple low power boost converter to ~18V, with a couple of schottky diodes and caps to generate the negative output. This, rather than a dedicated charge pump like the MAX868 has a few advantages:1) Because the positive output voltage has feedback, you can adjust its output voltage. So the negative output might not be the same as the positive, but you can adjust it so the negative output is at a voltage that you need when the circuit is drawing the same current as your LCD.2) There are thousands of boost converter devices on the market, often requiring a handful of external components that just "work". The suggestion from analog is a good one, but almost any boost converter that has a maximum output voltage of >22 (for a safety margin) at an input of ~5V will do. And given the low current requirement, you can narrow down the search by maximum output current to <100mA. Even <50mA is fine.I'm sure the original circuit is quite clever, but yeah.. custom magnetics can be unobtanium, and the original board is more than big enough to make a clone board with a boost converter and charge pump on it.

author: mariush
author_rank: Super Contributor
timestamp: August 30, 2025, 12:43:22 am
content: You can use a small boost regulator to make 5vFor example ISL9113 is available as a 6 bump bga chip, 3mm by 2.6mm or as 8DFN chip (2mm x 2mm)ISL9113EIAZ (adjustable version)https://www.digikey.com/en/products/detail/renesas-electronics-corporation/ISL9113EIAZ-T/4031648ISL9113ERAZ (adjustable version)https://www.digikey.com/en/products/detail/renesas-electronics-corporation/ISL9113ERAZ-T/3621607All you need is a 2.2uH inductor (can be as small as a 0805 - 1206 footprint), a couple input and output capacitors and the two resistors to set the output voltage.The negative rail, you could probably do it with a mc34063 or mc33063 but with lots of big components aroundOn the more expensive side, a LM2611 could easily do -18v with 5v input :https://www.digikey.com/en/products/detail/texas-instruments/LM2611BMFX-NOPB/1870997orhttps://www.lcsc.com/product-detail/C2072505.html?s_z=n_lm2611MAX17579 / MAX17580 is also an option (fewer external components but more expensive IC) :https://www.digikey.com/en/products/detail/analog-devices-inc-maxim-integrated/MAX17579ATC/14543079orhttps://www.digikey.com/en/products/detail/analog-devices-inc-maxim-integrated/MAX17580ATC/14543152

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 30, 2025, 11:24:33 am
content: Quote from: Buriedcode on August 29, 2025, 11:18:42 pmMy suggestion was a generic boost converter to +5V with an attached cascade voltage multiplier to get a little less than (-4)*5V, approximately -18V.Of course, generic boost converters are that cheap that there is little reason to not use a second dedicated one for -18V with better adjust-ability.EDIT: I´m thinking of a circuit like this:http://www.chrisgreenley.com/projects/charge-pump/- Just taking the existing +5V-boost converter as the oscillator instead of the transistor part of the circuit.

author: EliotFR
author_rank: Newbie
timestamp: September 01, 2025, 09:11:21 am
content: Thank you for all your answers.I gave up for the charge pump asembly because I'm afraid of making mistakes in some values.I should test in real conditions before launching a PCB, but that takes a lot of time.Electronics is a passion but my time is limited.For the 5V dc converter, i use the TPS61023, good efficiency and really cheap.I finally retained mariush's idea, with the MAX17580ATC. ( 17579 have a poor efficiency at low current ).not that expensive ( 2.8€ ) but really hard to find. I only find it at Mouser.My draft :C1 / C2 / C6 / C8 are optionals (I just copied from the datasheet).Because they can conflict with C29 / C30 / C32 / C33 (which are already on the motherboard PCB, cf first post ).

author: Haenk
author_rank: Super Contributor
timestamp: September 02, 2025, 06:56:26 am
content: How do you know the inductor is broken - is it physically ripped off the PCB or cracked?Usually, these never fail with low currents.However I would suggest checking the capacitors, I have seens recapping kits for other Gameboys, so one could assume these are not any better...

author: EliotFR
author_rank: Newbie
timestamp: September 08, 2025, 07:58:26 pm
content: Quote from: Haenk on September 02, 2025, 06:56:26 amUnfortunately, yes I'm sure.I think it fell somewhere.this pcb is in the bottom edge.I've unsoldered the module and tested it, and it still had 0V output.After measuring pins 1-4, the primary winding was "OL" :'(

author: Buriedcode
author_rank: Super Contributor
timestamp: September 08, 2025, 09:42:14 pm
content: I searched on Aliexpress and found a transformer for the gameboy pocket, but it appears to be for a different part of the circuit - not mounted on a sub board. But I did find:https://github.com/Gekkio/gb-schematics/blob/main/DC-CONV2-DMG-D/schematic/DC-CONV2-DMG-D.pdfI'm sure you've seen this before. There appear to be several versions but they are all pretty much the same - except this one has an undervoltage lockout circuit.So, I guess the problem is still the same: 2xAA to 5V + ~-18V for the LCD. As many have stated here, the battery to 5V is easy - standard boost converter.For the VEE rail - If this isn't for mass production - its a one-off to repair your Gameboy, or perhaps a small run for others, I see 3 options:1) Charge pump running off the switching node of the boost converter. For -18V, and the switching node going 5V p-p , thats 4 stages, which will give 4*5 = 20V, minus diode losses so about -18V.Usually over a couple of stages and the votlage sag can be significant, even for low currents, so 4 is pushing it. I've done it before, but t can destabilise some boost converters, so might need "tweaking" which is annoying.2) Seperate converter for the VEE. I've used a MAX868, or MAX749 in the past for LCDs, but they are expensive and not easily available, I'm sure there must be some cheaper "inverting buck boost" converters about.2a) As mentioned before, another boost converter boosting 2xAA to 18V, then a single stage charge pump off that will produce ~-18V. There are plenty of small low power boost converters that can boost ~3V to 18V. TPS61040 for example. Plus it'll be adjustable.3) A coupled inductor with ~3.5 the turns of the primary. There are some couple inductors with several identical windings on the same bobbin, so you can wire some in series to get a 1:4 ratio. You use the primary for the boost converter, and the secondary for the negative voltage. Its a one-inductor-onechip solution, but such coupled inductors are very rare, especially for the small current/size of that board.Out of all the above, I'd go with 2a. Should fit on a similar sized board.

author: langwadt
author_rank: Super Contributor
timestamp: September 08, 2025, 09:50:46 pm
content: something like this?https://www.digikey.dk/en/products/detail/pulse-electronics/PH9585.003NLT/14552051

author: Someone
author_rank: Super Contributor
timestamp: September 08, 2025, 11:42:25 pm
content: Quote from: Buriedcode on September 08, 2025, 09:42:14 pmBuck as negative regulator:https://www.ti.com/lit/an/snva856b/snva856b.pdf

author: themadhippy
author_rank: Super Contributor
timestamp: September 09, 2025, 12:04:32 am
content: could always try rewinding the inductor,just count the number of turns as you take them off so you know how many to put back

author: EliotFR
author_rank: Newbie
timestamp: September 09, 2025, 07:54:26 pm
content: Quote from: themadhippy on September 09, 2025, 12:04:32 amYou're overestimating my skills.The wires, in particular, seem like a real tangle.There's no way I'll be able to pull them back together afterward.Quote from: Buriedcode on September 08, 2025, 09:42:14 pmThe good one is the "LSEP01088A1" :https://github.com/Gekkio/gb-schematics/blob/main/LSEP01088A1/schematic/LSEP01088A1.pdfThanks for all your advices, I'll keep thinking about it.