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SMD transistor/ic "5131Z"


Well-Known Member

This 3 leg component (looks like any other smd transistors) is found within an old HP 930C printer from 2001, more specific it is located at the internal power supply board, hi voltage side.
I haven't done any attempt to draw the schematic, doing so may help identify it's real type.

However, I'm interrested in being able to work out what kind of component it is based on it's printed number - if possible.

So far, google haven't being of any help - only wasted my time redirecting to click-bait websites (I mean, those that list up millions of part numbers at once just so someone get to follow its links).

PCB board:
HP PART NO : C6426-60081
white label underneath: B266816R1 0103


Well-Known Member
Bumb. No one have any idea?

From what I know about it for now, the pin-3, normally collector if standard BJT is connected to rectified minus at primary side (there is no designated gnd on this so I go with "minus" notation for now).
Pin1 (usually base if being standard bjt model) connected to a diode anode, feed from L from before rectifier via resistor network.
Pin2 connected to pin 1 on a AS998 PWM controller, 0V input (ok, I struggle to find any reference online what function that "0V" pin should have)


Well-Known Member
Ok, so I have worked out how the scematic are probably assembled.

It seems like it is most likely a NPN BJT, so it's kind of guess work about this.

I opted to use some non-standarized symbols (HP made it kind of hard to trace so I did too), as including the zeero-value smd resistors. This was only including for make it easier for me to trace, and just didn't remove.

None of the SMD components was labeled, so I had to make those up (all labeled components above 100 are SMD mounted).

What make this SMTP interresting is that the controller unit ( IC1 ) take feedback from both voltage and current as well as mains voltage.



Well-Known Member
I would suggest more like over current protection rather than feedback?.
Yes I'd think that as well - but for the "OV" input, the datasheet for the AS998 pwm controller says (link):

Overvoltage pin.

The OV input/output function is implemented by an on-chip latch.
This pin is driven to the Reg voltage if the on-chip circuitry senses a VDD level greater than the OV threshold (VDDov). This error condition stops the part from generating any more output pulses until VDD has been reduced to the VDDul level and then raised as in a normal power-on sequence.

Alternatively, the OV error condition can be cleared by forcing the OV pin to near ground.
The output is immediately enabled following an OV clear function.
The OV error condition can also be generated externally by temporarily forcing the OV pin to a voltage greater than the VOV threshold. This will force the part to latch an OV condition and not generate any more output pulses unless cleared as described.
The sentence I've underlined is the one that I cannot make sense of. Or - maybe the datasheet is incomplete and that pin can be used as overcurrent as well ?

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