Component identification SOT-223

[saronno]

this little baby is marked R54 BH ... is it a npn BJT? A MOS? A LDO?

I can't find anything online and also in the smd code databook ....

[saronno]

[martin1454]

Are you sure its R54 BH and not R54 13H? Its from On semi

[saronno]

It could be, I am not sure. As you can see in the photo, the R is similator to the B, in the sense the font look similar and with a little space in the middle.

[martin1454]

Well, it could be an BCP56T1G, if you look at the datasheet, it can have the marking "BH" in a sot-223 package( see page 5)
https://www.onsemi.com/pub/Collateral/BCP56T1-D.PDF
Where was it installed?

[saronno]

Red is 12V
Black is GND
Remaining colors are not a particular line. For example the blu lines are not one track. If they are not connected each other
they are different tracks.

The R54 are the one near 10v print on the board, very near the component who blown up (a zener considering the mark on the board).

Below is a sketch of the circuit ...

[saronno]

"Bruciato" means blown up0

As you can see I guess r54 are a BJT.

This part of the board is responsible for charging the battery
and power up the flash and the microcontroller on board (LDO, 3.3V power up flash and uC).
The battery is a 7.2V battery niMH

[saronno]

R54, if a BJT, it's faulty, since C and E is shorted (in both direction) and B (first pin on the left) is isolated from both of them.
This make me think that it could be also a mosfet (so B are not a base but a gate) .... I am not completely sure.

[saronno]

Another thing make me a bit upset is the LDO temperature.
The PSU is 12V rate .... since there is just a diode between 12V line the the input of the LDO it has to disssipate
about 7-8V (11-3.3). So, of course, it get very hot.
If PSU is unplugged an dbattery is charged, of course, LDO is power up throug the schottky diode (SKT+).

[saronno]

I forgot .... do you agree the blown zener should be about 8v?
I guess 8v since there should be at leat 7.2v+0.7v on the base to have the BJT in conducting mode.
An when the battery voltage is 7.2v+ Vbe goes down, shutting down the BJT.

[saronno]

Probably higher than 8v ... since 7.2 is nominal ... fullly charged (1.6v for cell) is 9.6 ...
it was probably 10v the zener who blown up.

[Kartika]

Yes  BCP56-16T1G Marking BH-16 SOT-223 NPN Silicon Epitaxial Transistor 80V 1A
BCP5616 SOT−223

[gnuarm]

"Bruciato" means blown up0

As you can see I guess r54 are a BJT.

This part of the board is responsible for charging the battery
and power up the flash and the microcontroller on board (LDO, 3.3V power up flash and uC).
The battery is a 7.2V battery niMH

I think I see an error in the schematic.  The 1k  resistor on the transistor base, is supposed to go to +12V, not the Zener diode.  The Zener connects directly to the base, no? 

The burnt Zener diode should be around 8 volts, give or take.  It is the voltage reference for the transistor in question, along with the 5.6 ohm resistor to control the current limit for charging, when the battery voltage is low. 

The other transistor, with the 12 ohm resistor on the emitter, is probably set for a trickle current.   Once you move the 1 kohm resistor on the schematic this makes sense.  But it's hard to know which transistor is trickle and which is main, because of the multiple Zeners without voltage specs.