augustinetez
Active Member
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.
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.