Sorry, it's early morning here and I'm apparently not fully awakened yet. Meant to say that it was the lowest Rds(on) P-channel FET I could find in a SOT-23 package from LCSC, which is where I shop most of my components. You'd be able to get away with a slightly higher Rds(on) FET. If it's too high though, it will start to affect the efficiency, leading to a higher current consumption when on, due to the boost converter compensating for the voltage drop.
mandag den 7. juni 2021 kl. 07.10.53 UTC+2 skrev Christian Riise Wagner: > The MMBTA42 is a bipolar transistor and not a FET. Secondly it's NPN, > making it unsuitable as a high side switch, because the base needs to be at > least at 0.7V higher than the voltage at the emitter for the transistor to > turn on. I used a Winsok WST2339 because that was the lowest Rds(on) > P-channel FET I could find in a SOT-23 package. However you will no doubt > be able to find something similar from Mouser, Digikey, etc. It will be > active low, so the gate should be connected to the input voltage rail > through a pull-up resistor. Your microcontroller will then have to pull the > gate low to enable the power supply. If the supply voltage of the power > supply is within the voltage rating of your microcontroller's GPIO pins, > you can connect it directly. If not, you should use a N-channel MOSFET or > an NPN transistor to pull the gate low. > søndag den 6. juni 2021 kl. 22.24.19 UTC+2 skrev [email protected]: > >> That's great to hear as a confirmation. As soon as I get a chance to >> spend some time on the bench, I'll give it a try. It should be quick >> enough. I'm going to use a standard MMBTA42, please let me know what you >> have used, if you can share that piece of information. >> >> Thanks Christian. >> >> Il giorno domenica 6 giugno 2021 alle 21:17:00 UTC+1 Christian Riise >> Wagner ha scritto: >> >>> I've successfully used a P-channel MOSFET as a high side load switch for >>> a LM3478 based tapped inductor booster. IIRC the off current was >>> immeasurable, so sub 100nA. >>> søndag den 6. juni 2021 kl. 19.33.50 UTC+2 skrev [email protected]: >>> >>>> Thanks David, indeed you are absolutely right. The power supply with >>>> LT1308B is very reliable and not as sensitive to layout design as other >>>> ones that I have tried. >>>> >>>> LT1308B has in Iq of 0.01uA in stand-by, as you say. I've built your >>>> nixie watch (picture attached) and in my design it seems to use 2.3uA. If >>>> I >>>> build the HVPS on a breadboard, I can measure 0.1uA or less, which is >>>> great >>>> (I guess the resolution of my multimeter Keysight U1241B cannot measure >>>> less than 0.1uA accurately but that's great at 0.1uA or less). Of course I >>>> have tried to troubleshoot my LT1308B HVPS with no success. In my quest >>>> for >>>> a more efficient HVPS, I have designed a power supply using the MAX668 >>>> chip (as per datasheet and similar to many commercial HVPS), this was >>>> tricky to design with no noise, it works well now (after 6 different >>>> designs) however the stand-by power is 2.4uA, as per datasheet. So I can >>>> have higher efficiency than with LT1308B but also higher stand-by current >>>> (I believe because MAX668 has an internal LDO). >>>> >>>> Which is why I was thinking whether I can use a high load switch to >>>> truly bring shutdown current to zero using a power supply built around >>>> MAX668. Of course, this is a bit of a (pointless) extreme challenge to >>>> reduce stand-by current as much as possible to break even with solar >>>> panels, but that's where the fun is for me. And of course I could keep on >>>> troubleshooting the LT1308B design, it actually works perfectly other than >>>> it gives me higher stand-by current than on the datasheet, not sure if >>>> that >>>> depends on the design layout. But then again, I'm only a hobbyist and not >>>> an engineer, so I may be missing something. >>>> >>>> So any suggestions on why my LT1308B draws more than 1uA with SHTN=0V >>>> welcome (I have tried 4 different chips, same thing on the PCB, fine on >>>> the >>>> breadboard). Or any other suggestions to use any other power supply with >>>> perhaps a high load switch to bring standby current to less than 1uA, >>>> which >>>> I worry is unnecessary additional components and introduces a potential >>>> start-up delay. >>>> >>>> >>>> Il giorno domenica 6 giugno 2021 alle 18:12:46 UTC+1 nixiebunny ha >>>> scritto: >>>> >>>>> Max, >>>>> The LT1308B has a .01 uA typical, 1 uA maximum standby current when >>>>> shut down, according to the data sheet, shown on page 2 as Iq (the >>>>> third line with Vshdn = 0V). >>>>> >>>>> I don't think you have a problem here. >>>>> >>>>> >>>>> On 6/6/21, Max DN <[email protected]> wrote: >>>>> > Hello, >>>>> > >>>>> > I'm working on a solar powered nixie watch (similar to the Kopriso >>>>> Nixie >>>>> > watch). >>>>> > >>>>> > It's crucial that I dramatically reduce stand-by power as much as >>>>> possible >>>>> > and within 2.5uA, which is where the solar panels will balance off >>>>> the >>>>> > stand-by current. >>>>> > >>>>> > Regardless of which power supply I use, even using the shutdown pin, >>>>> the >>>>> > power supply still takes 2.5uA. This is perfectly in line with the >>>>> > electrical specifications of the datasheets. >>>>> > >>>>> > So, my question is, can I 'brute force' a shutdown, effectively >>>>> removing >>>>> > the power from the VIN pin via a PNP high speed mosfet such as >>>>> MMBTA42 or >>>>> > it will introduce too much of a delay in starting the power supply? >>>>> > >>>>> > I'm going to try it on the fly but if anyone has any suggestions on >>>>> how to >>>>> > bring to 0 or to 0.01uA the stand-by current that would be great. >>>>> > >>>>> > As an example, I'm using the LT1308B DC/DC converter as on page 17 >>>>> of the >>>>> > datasheet >>>>> > >>>>> https://www.analog.com/media/en/technical-documentation/data-sheets/1308abfb.pdf >>>>> >>>>> > >>>>> > Any suggestions will be much appreciated. >>>>> > >>>>> > Thank you, >>>>> > Max >>>>> > >>>>> > -- >>>>> > You received this message because you are subscribed to the Google >>>>> Groups >>>>> > "neonixie-l" group. >>>>> > To unsubscribe from this group and stop receiving emails from it, >>>>> send an >>>>> > email to [email protected]. >>>>> > To view this discussion on the web, visit >>>>> > >>>>> https://groups.google.com/d/msgid/neonixie-l/d45edcd8-0176-4205-95f1-b04eb34a32f1n%40googlegroups.com. >>>>> >>>>> >>>>> > >>>>> >>>> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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