Help needed to identify SOT23 component 418Q1

[fripp]

Can anybody help me identify the component in the picture below.  SOT23 symbol 418Q1.  I believe it is a voltage regulator but it seems to have failed.  Not sure what the output voltage should have been.  Closest I have found is Fortune FS8854 but they don't list Q1 as a voltage option on the datasheet I can find. And it seems to be obsolete now.  Manufacture date was 2019.

[fripp]

Reverse engineering has given me this schematic, but no clue to actual voltage from the 418Q1 regulator.  It is powering switched mode voltage sensing control circuitry from a 12V battery charger.

Any insights or strategy to progress gratefully welcome.

At the moment the output voltage from the regulator just tracks the input voltage up to 14v, I haven't taken it higher.  When the VAC is supplied to the Switched Mode PSU it constantly trips into over voltage mode and resets every few seconds or so.  I think this is from the 431 Zener detecting the over voltage in the control circuit supply and tripping the opto.

[JohnE]

Hi Fripp, I came across your post while searching for info regarding the very same pcb and your schematic was very helpful - many thanks!

Did you get any joy with the 418Q1 V reg part? Mine is marked 418Y2 and with an input of 14v the output is less than 1v.

I do have another fully functioning board that surprisingly outputs around 13v from the V reg.

The faulty charger is outputting around 35v but not overvoltage tripping as I think yours did.

Hope you get to see this post!

[Hamelec]

Hi John,
ask here (prefered in German):
https://www.mikrocontroller.net/forum/analogtechnik
normally you will get a fast response by the user hhinz
regards

[Kean]

Based on the two provided marking codes, the actual part of the marking that is likely to be useful will be 41 or 418, with the Q1 or Y2 suffix being related to manufaturing location/date code/batch/whatever.

No idea on the actual part, but on first glance to me with that resistor divider I'd assume a P-Channel MOSFET controlling power to some parts of the circuit.

The reverse engineered schematic by fripp doesn't make much sense and so may have some errors.  For example pin 1 of this SOT23 device (potentially the P-Ch gate) is shown connected to two 10k resistors R30 & R32, but we can only see one in the photos.  That would be R32 which would thus turn on the P-Ch FET when U3 optoisolator is on.  But the power for the LED in that opto comes from the same supply which apparently originates through this same unknown part?

Another weird section of the schematic is around Q1 which seems to be a zener diode based regulator for the PWM controller power, but the supply comes from Vdd and it outputs also to Vdd.  Clearly that wouldn't be right.

I guess this could be part of a latching power enable, but it is hard to work out with potential schematic errors and unknown connected circuits on the 3 pin headers.

[JohnE]

Many thanks for your observations, Kean.

Yes, I also have spotted some anomalies in Fripp's schematic but there's no criticism - it's a useful starting point.

I've renamed Vdd on the 'isolated' side to Vcc, and this has helped get my head around the problem of Vdd trying to pull itself up by its own boot straps.

Trying to make sense of the schematic and came to the same conclusion as you did regarding the V Reg - it does makes more sense being a MOSFET.

As the thing is working of sorts (outputting 30 odd volts as opposed to 14V) I'm suspecting a pwm problem.

Again, thanks for your comments and I'll post the conclusion in due time, but at the moment I'm tearing my hair out watching England's abysmal performance against DR Congo!

Cheers, John

[JohnE]

Solved!

Yes it's a P Ch Mosfet and not a V reg, and after fitting a suitable device the charger is outputting 14.4v as advertised.

Many thanks for the help!

[Kean]

Great to hear, and thanks for the update.

To potentially help others in future with search results, what was the make and model of the charger?

[JohnE]

German manufacturer Schaudt (now Lippert).

Model CSV409, caravan (trailer) leisure battery charger and distribution module.

Other models in the series include CSV402, CSV413, CSV414, CSV416 and probably others.

They include switch-selectable charging profiles for either lead acid or gel batteries and I'm looking into the feasibility of a conversion to a Lithium (LiFePO4) profile.