SMD part "VG73" (SOT-23-6) - Solar lamp circuit - Page 1
Forum section: electronics / beginners

author: thymjan
author_rank: Contributor
timestamp: December 28, 2024, 08:45:11 pm
content: Try to repair a defective solar lamp. I have already replaced a slide switch with a loose connection.Still doesn't work. Now I identified a defective SMD part (compared with a functioning lamp).Does anyone know what this VG73 could be?Only four of the six pins are used.B+ and B- is batteryS+ and S- is solar cellAny help appreciated.

author: Konkedout
author_rank: Frequent Contributor
timestamp: December 28, 2024, 09:52:35 pm
content: Why not try to draw a schematic diagram as well as you can? From the looks of that pcb, drawing a schematic ought not be so difficult.If you can draw and post that, I think you would be more likely to get a helpful response.

author: thymjan
author_rank: Contributor
timestamp: December 28, 2024, 11:03:14 pm
content: Thank you for your reply.I tried to do a part schematic:

author: prints-f-darkness
author_rank: Contributor
timestamp: December 29, 2024, 06:26:00 am
content: Hi,It might be a battery protection IC, your schematic looks similar to the app notes for the AP9211.https://www.diodes.com/assets/Datasheets/AP9211.pdfWhich protection IC, I have no idea.Its most likely a Chinese brand IC, like the DW01Ahttps://www.lcsc.com/product-detail/Battery-Management_HL-DW01A_C18164398.html

author: thymjan
author_rank: Contributor
timestamp: December 29, 2024, 07:19:18 am
content: Hi, thank you for your reply.This makes sense. There are three NiMH AA (in series) batteries inside.I'll have a deeper look at the website.

author: inse
author_rank: Super Contributor
timestamp: December 29, 2024, 07:29:07 am
content: Usually there is D for Diode, Q for transistor and U for IC.This circuit confuses me

author: thymjan
author_rank: Contributor
timestamp: December 29, 2024, 01:17:05 pm
content: This was my guess. The parts look like transistors, but are marked with U. Should I treat them as ICs you think?I didn't find data sheets for "42JD" either.

author: inse
author_rank: Super Contributor
timestamp: December 29, 2024, 03:53:05 pm
content: I appreciate your effort but once you have to order parts like the ominous VG73 IC, the repair is futile from economical point of view.Or is it a high-class decoration?

author: fzabkar
author_rank: Super Contributor
timestamp: December 29, 2024, 06:58:41 pm
content: Quote from: thymjan on December 29, 2024, 01:17:05 pmThere is a Q1 at the right hand edge of the PCB ...

author: thymjan
author_rank: Contributor
timestamp: December 29, 2024, 07:22:17 pm
content: I already spent some effort to repair the lamp. In some point of view it’s useless, but the other way to throw away a hole lamp only because of a defective little 3mm part – wouldn't a repair be nice?I didn't know it would be such a struggle to get a spare part.

author: thymjan
author_rank: Contributor
timestamp: December 29, 2024, 07:28:02 pm
content: Quote from: fzabkar on December 29, 2024, 06:58:41 pmSo you think I should draw my schematic sketch once again?Till now I didn‘t understand how this circuit functions.Are MOSFETS signed with Q or U?

author: inse
author_rank: Super Contributor
timestamp: December 29, 2024, 07:30:50 pm
content: Unsolder one and test it.

author: prints-f-darkness
author_rank: Contributor
timestamp: December 29, 2024, 09:23:45 pm
content: *strokes my beard in thought*- you want to save the lamps.- you need a working circuit for that.why not design a new pcb?or buy a driver board online?https://www.aliexpress.us/item/3256805471942913.htmlI've actually become quite invested in your post, it would be really neat if the forum came together and helped you design a new pcb for your lamps. It would help reduce garden light waste all around the globe, quite the environmental project if you ask me.I can say, the BQ2971 looks like a winnerhttps://www.ti.com/lit/ds/symlink/bq2971.pdfapp notes / EVM,https://www.ti.com/lit/ug/sluuaz3/sluuaz3.pdfI assume U1 on your PCB to be a led driver of sorts, and you may find some uber simple garden light design online that you can adapthttps://www.instructables.com/Simple-Solar-Circuits/That's just my advice anyway, ill leave ya to your devices and or components.(also I would like to see a high res image of both front and back of the PCB and a pic or two of this awesome lamp we are trying to save)

author: fzabkar
author_rank: Super Contributor
timestamp: December 30, 2024, 01:44:55 am
content: Quote from: thymjan on December 29, 2024, 07:28:02 pmCould the U parts be digital transistors (with resistors in the base)?

author: thymjan
author_rank: Contributor
timestamp: December 30, 2024, 04:49:08 am
content: Here is a link to the instruction manual:https://www.solarversand.de/media/pdf/cf/d3/03/102530-GB-2023.pdfThe other side of the pcb:I allready asked the manufacturer for help to identifying the part and awaiting his answer.U1 is a NAND Gatter with Schmitt-Trigger (74HC132D CSM54806 TXD1803D).There are also to slide switches wintermode/off/summermode and warm/cold white and a motion detector.

author: inse
author_rank: Super Contributor
timestamp: December 30, 2024, 05:17:54 am
content: Why are there no cables at the positions S+ and S- which you identified as solar cell connection?

author: thymjan
author_rank: Contributor
timestamp: December 30, 2024, 06:38:44 am
content: I had to take them temporarily off to make a decent photo.

author: inse
author_rank: Super Contributor
timestamp: December 30, 2024, 07:08:55 am
content: If identification and/or sourcing of the VG73 part should prove impossible, either a workaround needs to be implemented or the lamp discarded.I would be surprized if there was an elaborate charge circuit implemented.Usually those solar lights only limit the voltage on the battery terminals, an undervoltage cut off would also be beneficial.A 4.7V zener should serve as overcharge limiter, undervoltage cut-off would require a comparator or a reset generator as proposed in this thread:https://www.eevblog.com/forum/projects/tl431-rgb-led-for-power-on-low-battery-indicator/25/Or you get a protected LiIon cell that includes all the above and replace the NiMHs

author: fzabkar
author_rank: Super Contributor
timestamp: December 30, 2024, 09:31:38 am
content: U6 is driven by U1 via a 100 ohm resistor. That suggests that U6 is an N-channel MOSFET with logic-level gate drive.Perhaps U = MOSFET, Q = BJT?

author: inse
author_rank: Super Contributor
timestamp: January 01, 2025, 07:08:27 am
content: U=MOSFET and IC? This appears strange…thymjan, did you give up on the lamp or shall we continue?

author: inse
author_rank: Super Contributor
timestamp: January 02, 2025, 05:53:39 am
content: I guess that U3 is a kind of undervoltage detector to prevent the battery from being deep discharged.Little anything else than a N-MOSFET makes sense for U5 as interruptor for the battery negative terminal.Is there a connection from battery plus to the K+ terminal? Otherwise I could not figure out how the battery would power the circuit.And where is the switch connected that you mentioned (SUM/WIN/K1?)I wonder how U3 should have failed but if apparently so and no success identifying AND sourcing it, we need to find a work around.As proposed before, a protected LiIon cell could be placed between K+ and S-, bypassing the onboard protection circuit.Voltage would be similar to three NiMH cells.

author: thymjan
author_rank: Contributor
timestamp: January 02, 2025, 05:15:32 pm
content: QuoteSorry, this part I missed. Here are the schematics of the slide switches:QuoteI measured a sort of short between the two-pin-side of U5. I removed R9 and C7. Nothing happened. Only when I removed U3 the short circuit was gone.QuoteI don't know if a LiIon cell will perform well at -10° Celsius. Is this a better use case for NiMH cells?I try to recover the schematics with scheme-it (DigiKey). I have a bit of a struggle to draw the unknown parts there. Do you have a better recommendation for beginners?

author: inse
author_rank: Super Contributor
timestamp: January 02, 2025, 06:13:13 pm
content: I don’t know the program but I do schematic design on a professional basis.For side projects, colleagues now switch to KiCAD, which I haven‘t used yet, I used Eagle as well.All batteries suffer at low temperatures but as the solar light is only consuming a relatively low current and the solar cell won‘t do fast charge as well, the increased impedance is probably of less concern.The idea behind my proposal is that protected cells include over- and undervoltage protection, so you could skip the defective circuit.Otherwise you would have to repair it or design a new one…

author: thymjan
author_rank: Contributor
timestamp: January 03, 2025, 08:47:20 am
content: For a better understanding:U3 is measuringthe battery voltage. U5 is a normally opened switch, which only closes if U3 is measuring a certainminimal voltage. If battery voltage is ok, S- and B- are connected.What could be the function of R10?

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 09:49:59 am
content: If you‘d switch open by closed, I‘d agree.I assume the switch is a N-MOSFET as there is no base resistor also it needs to conduct in both directions to enable charging and discharging.Not sure about the sense(?) pin and R20, maybe it detects solar voltage and turns on the switch for better charging?

author: thymjan
author_rank: Contributor
timestamp: January 03, 2025, 04:54:22 pm
content: I mean the component. In the circuit with operating battery the switch should be closed, is it?

author: inse
author_rank: Super Contributor
timestamp: January 03, 2025, 05:00:28 pm
content: Quote from: thymjan on January 03, 2025, 08:47:20 amSorry for my unclear phrasing.I assume U5 a N-MOSFET and it should be ON in normal operation and OFF if U3 detects battery undervoltage.

author: thymjan
author_rank: Contributor
timestamp: January 04, 2025, 12:16:33 am
content: Here is my first try with KiCad. There are still some wrong components which I didn't find. But KiCad is quite nice for doing thisAnd it's a little bit upside down ...If someone knows tricks to get a better view, let me know!

author: inse
author_rank: Super Contributor
timestamp: January 04, 2025, 05:24:55 am
content: Nicely done for a (Ki-)CAD starter but honestly spoken it’s a waste of time to capture the schematic outside of U3 and U5 as this is only LED control.So how do you plan to go on from here?I made my proposals, what is yours?

author: thymjan
author_rank: Contributor
timestamp: January 05, 2025, 07:23:17 am
content: Still looking for a replacement for the VG73. Also still awaiting answer from the manufacturer of the lamp.Maybe it's a sort of DW01 derivative?

author: inse
author_rank: Super Contributor
timestamp: January 05, 2025, 07:37:15 am
content: DW01 appears comparable, why not give it a try.See if you get one separate or whether desoldering from a cheap BMS is more reasonable.Bypass the MOSFET for a test if the rest still works.Btw, you‘re not seriously expecting support from the lamp manufacturer?

author: thymjan
author_rank: Contributor
timestamp: January 05, 2025, 08:30:15 pm
content: I bypassed the protection circuit by connecting B- with S-. Now the LED is always on. Regardless of whether light falls on the solar module or not.Whether something happens at the motion detector or not. In winter mode the brightness only gets full when motion appears. I would have expected this is still functional.It is also not clear to me how charging the battery works.I think I give up.

author: inse
author_rank: Super Contributor
timestamp: January 05, 2025, 09:07:21 pm
content: Oh, what a pity…How did it get damaged anyway, batteries installed backwards or hit by lightning?The charging path is from S+ to K+, via the switch to B+, from B- backwards through U5 to S-