Timeline for Press ON - Hold OFF latching circuits
Current License: CC BY-SA 3.0
21 events
| when toggle format | what | by | license | comment | |
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| May 1, 2017 at 13:16 | comment | added | Andy aka | Will a 10 k resistor be too high do you think? It's all down to getting the leakage currents as low as possible of course. | |
| May 1, 2017 at 13:13 | comment | added | GPTechinno | after 1 more day testing it, yes i come to conclude it should have been a bad mosfet on the first prototype... The MBR0530 is fine, just need to add a resistive load of 1k on top of the real load... It is for a battery operated system, so this 1k will reduce autonomy overall... anyway... | |
| May 1, 2017 at 13:12 | vote | accept | GPTechinno | ||
| May 1, 2017 at 9:18 | comment | added | Andy aka | Possibly a defective mosfet maybe? | |
| May 1, 2017 at 9:13 | comment | added | GPTechinno | I just soldered a new prototype, without any load, just a 1k resistor (and the MBR0530), now the OFF Latch is locked, full functionnal !!! I will be adding my (capacitive) load 1 by 1 to see at what point the switched OFF rail is no more 0V... | |
| May 1, 2017 at 9:09 | comment | added | GPTechinno | I am using only ceramic capacitors, so non polarised. | |
| May 1, 2017 at 8:35 | comment | added | Andy aka | Non polarised capacitors? | |
| May 1, 2017 at 8:19 | comment | added | GPTechinno | About the diode reverse current leakage, I have tried removing the MBR0530, so have no more current leakage, and the only missing function is the HOLD-OFF because C11 cannot discharge through R15 and D1 anymore. But I still have the auto-ON or broken latch-OFF... My understanting is now the latch-OFF cannot hold because OFF state is not properly grounded -> see the 1,7V above. | |
| May 1, 2017 at 8:12 | comment | added | GPTechinno | Still with MBR0530, plugged the oscilloscope on the switched 3,3V rail while in OFF state (continuously press button), and here is the 1.7V I saw with voltmeter before : [![enter image description here][2]][2] [2]: i.sstatic.net/Dmn1S.png We can see periodic 80ms bumps... where does this come from ? | |
| Apr 29, 2017 at 10:15 | comment | added | GPTechinno | Looking at what I have in stock, I may try the DFLS1100 with a Ir of 100nA (more in the range of the BAV99). Keep you updated after testing. | |
| Apr 29, 2017 at 10:08 | comment | added | Andy aka | Well, you've seen it now! I just went to the data sheets and looked (just like you). | |
| Apr 29, 2017 at 10:06 | comment | added | GPTechinno | Where do you see the "bad leakage characteristic" of the MBR0530 ? I don't understand where to find this information in the datasheet. Should I compare the reverse current Ir in normal condition ? MBR0530 have 130uA and BAV99 is 25nA (lot smaller) ? Thanks to teach me this point, I am not an expert... | |
| Apr 29, 2017 at 9:56 | comment | added | Andy aka | Ah, the MBR0530 - it has a really bad leakage characteristic and will keep the n channel fet biased on I suspect. The reverse current on the BAV99 is decades smaller. | |
| Apr 29, 2017 at 9:53 | comment | added | Andy aka | I can't help but think that maybe you've built it incorrectly. Have you used non-polarized capacitors i.e. NOT electrolytics? If you short the gate of the n channel fet to ground will it power off after a few seconds and importantly stay off? What current flows from the p channel FET (when it is meant to be off) if you load it with 100 ohms? The 1.7 volts doesn't sound great. | |
| Apr 29, 2017 at 9:49 | comment | added | GPTechinno | So I added real board load (2 MCU + other ICs), and it didn't fix the broken OFF state latch. I added a 10k load resistor, not better result. 1k -> same. I am really thinking this is due to the MOSFET I am using how has very low Vgs(th) of 0.45V and so the latch is not strongly locked... There is more, now I have the full load, when in OFF state, I still can measure 1.7V on the switched 3.3V rail (should be closer to 0V) !!! I will plug the oscilloscope to see if this 1,7V is DC or some kind of oscillating voltage... | |
| Apr 28, 2017 at 18:28 | comment | added | Andy aka | Feel free to try 1 kohm too just in case the p channel fet is leaker than it says in the data sheet or has been subject to bad handling that may have weakened its insulation characteristics. Feel free to upvote and mark answer as accepted should it work! | |
| Apr 28, 2017 at 18:26 | comment | added | GPTechinno | ok, thanks a lot, i will continue testing tomorrow morning with the 10k load resistor. I will keep you updated here, of course. | |
| Apr 28, 2017 at 18:23 | comment | added | Andy aka | The led will not draw current until the supply has risen to a couple of volts and by then the deal is done. Assume maybe 10 uA can flow from the p channel mosfet so if you have a 10 kohm load resistor it should do the job. | |
| Apr 28, 2017 at 18:20 | history | edited | Andy aka | CC BY-SA 3.0 |
added 271 characters in body
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| Apr 28, 2017 at 18:15 | comment | added | GPTechinno | I see, this is a good point... During my first testing, I didn't mount full load the board will have. But it was not an open circuit neither, it had LED indicator for power status, around 5mA of current... I will try adding full load to see difference. | |
| Apr 28, 2017 at 18:10 | history | answered | Andy aka | CC BY-SA 3.0 |
