Led Torch schematic - thoughts?

[augustinetez]

The wifes favourite small LED torch has decided it's had enough (an old MXDL 1.5V 3W job), so I thought I would take a look.

Sure enough, disassembling it and powering the joule thief/inverter circuit shows no sign of activity - the LED works fine when powered independently.

The electronics comprises, excluding the LED, 4 components a transistor ?, diode, capacitor and inductor as per photo

But, I'm having difficulty with the circuit as I can't positively identify the transistor - the marking (badly scratched) appears to be M03p which leads to a quandary - M03 in SOT 23 shows up as a digital transistor DDTC123TCA which appears to have only been available since 2021 and the torch is much older than that. If it is a digital transistor, there would be a resistor in the base connection.

Below is the schematic as traced from the pcb if anyone can shed light on what it might be - the battery polarity would indicate PNP and yes the LED is drawn correctly which leads to another anomaly.

Everything appears to test OK without having removed the transitor, the diode is marked S4 and is a Schottky diode - the other side of the pcb is just two concentric pads for the battery positive and outer case to make contact (the vias' are good) - you screw/unscrew the body to turn it on/off.

 

[Tony Stewart]

This is a better match for M03

https://product.torexsemi.com/ja/system/files/series/xc61c.pdf

 

[eTech]

The wifes favourite small LED torch has decided it's had enough (an old MXDL 1.5V 3W job), so I thought I would take a look.

Sure enough, disassembling it and powering the joule thief/inverter circuit shows no sign of activity - the LED works fine when powered independently.

The electronics comprises, excluding the LED, 4 components a transistor ?, diode, capacitor and inductor as per photo

View attachment 145093

But, I'm having difficulty with the circuit as I can't positively identify the transistor - the marking (badly scratched) appears to be M03p which leads to a quandary - M03 in SOT 23 shows up as a digital transistor DDTC123TCA which appears to have only been available since 2021 and the torch is much older than that. If it is a digital transistor, there would be a resistor in the base connection.

Below is the schematic as traced from the pcb if anyone can shed light on what it might be - the battery polarity would indicate PNP and yes the LED is drawn correctly which leads to another anomaly.

Everything appears to test OK without having removed the transitor, the diode is marked S4 and is a Schottky diode - the other side of the pcb is just two concentric pads for the battery positive and outer case to make contact (the vias' are good) - you screw/unscrew the body to turn it on/off.

View attachment 145094

Current can never flow in the LED if wired the way you've shown.
Are you sure the LED is shown correctly?

The part number DDTC123TCA you've provided for the transistor specifies an Pre-biased NPN transistor.

 

[ronsimpson]

ZXSC380 OR 381? Shown here without the diode and cap. Works either way.

SMDPR4401 ?? https://diotronic.com/index.php?controller=attachment&id_attachment=834

 

[augustinetez]

PR4401 datasheet has the the exact circuit with diode and cap on page 8 so looks like the one, thankyou.

 

[Tony Stewart]

XC61 is partial p/n for code M03 which has a threshold of 2.0V close but no cigar.

Although similar, but not the same , but looks to have better specs for the boost current limiter.

 

[AnalogKid]

It is possible that the 3-pin device is in fact an integrated circuit, a boost converter chip with an onboard switch.

ak

 

[augustinetez]

More than likely - I couldn't find a match (other than the DTC one) for the code on it.

Thanks to the kind gentlemens' responses above, it would appear to be an IC for LEDs with an anomalous marking (possibly a house code?).

 

[Nigel Goodwin]

More than likely - I couldn't find a match (other than the DTC one) for the code on it.

Thanks to the kind gentlemens' responses above, it would appear to be an IC for LEDs with an anomalous marking (possibly a house code?).

Generally the codes on SM devices are completely meaningless, you need to refer to the service manual for the device (if such a thing even exists) to determine what it is.

 

[ronsimpson]

Thanks

Weldome,
I spent two years of my life designing LED torches for a large company. I know the ICs in post #4. We sold torches in the stores, with batteries, for less than the cost of the batteries. Battery prices are down now, but there is almost 0 cost in that torch. Most of the time the failure is in the mechanical switch, or the battery contacts. Sometimes the IC or LED fail but not often.

 

[augustinetez]

I did power the module directly and it is dead.

At this point, probably cheaper to buy her a new one than messing about trying to fix it.

Thanks all for the responses.