I built this circuit based on the examples in the datasheet. It worked.
Transistor Q3_1 is BUJ100LR,412Bipolar Transistors - BJT Bipolar Transistors - BJT Trans GP BJT NPN 400V 1A 3-Pin
https://www.mouser.ie/datasheet/2/848/BUJ100LR-1846655.pdf
C2_1 is 4.7uF Tantalum Capacitors 20V
https://www.mouser.ie/datasheet/2/40/avx_taj_e-1158783.pdf
Voltage at Vs is 16.3V (created by an internal zener).
Voltage at Vdd is 5V.
I thought perhaps I'll shrink those two devices, and replaced them with
Transistor Q3_1 with a NEXPERIA PMBTA45,215 Bipolar (BJT) Single Transistor, NPN, 500 V, 35 MHz, 300 mW, 150 mA, 100 hFE
http://www.farnell.com/datasheets/812952.pdf
C2_1 with 10uF Murata 0805 (2012M) MLCC 25V dc ±10% SMD GRM21BB31E106KA73L
https://docs.rs-online.com/671d/0900766b8145fba0.pdf
However, things didn't work.
Voltage at Vdd was 5V as expected.
However
* with the transistor installed, the Vs pin would oscillate between 13V and 15V. I don't have an oscilloscope, but the period was visible on a DMM. I removed the transistor (and thus, the L_Pwr feature), and then measured a stable 15V on Vs. This should be 16.3V as before.
* I replaced the 10uF with the original 4.7uF, and it worked - it was showing 16.3V, and the dimmer worked.
So how were my choices so very wrong!?
FL5150 examples/datasheet https://www.mouser.ec/datasheet/2/149/FL5150-1008825.pdf
Transistor Q3_1 is BUJ100LR,412Bipolar Transistors - BJT Bipolar Transistors - BJT Trans GP BJT NPN 400V 1A 3-Pin
https://www.mouser.ie/datasheet/2/848/BUJ100LR-1846655.pdf
C2_1 is 4.7uF Tantalum Capacitors 20V
https://www.mouser.ie/datasheet/2/40/avx_taj_e-1158783.pdf
Voltage at Vs is 16.3V (created by an internal zener).
Voltage at Vdd is 5V.
I thought perhaps I'll shrink those two devices, and replaced them with
Transistor Q3_1 with a NEXPERIA PMBTA45,215 Bipolar (BJT) Single Transistor, NPN, 500 V, 35 MHz, 300 mW, 150 mA, 100 hFE
http://www.farnell.com/datasheets/812952.pdf
C2_1 with 10uF Murata 0805 (2012M) MLCC 25V dc ±10% SMD GRM21BB31E106KA73L
https://docs.rs-online.com/671d/0900766b8145fba0.pdf
However, things didn't work.
Voltage at Vdd was 5V as expected.
However
* with the transistor installed, the Vs pin would oscillate between 13V and 15V. I don't have an oscilloscope, but the period was visible on a DMM. I removed the transistor (and thus, the L_Pwr feature), and then measured a stable 15V on Vs. This should be 16.3V as before.
* I replaced the 10uF with the original 4.7uF, and it worked - it was showing 16.3V, and the dimmer worked.
So how were my choices so very wrong!?
FL5150 examples/datasheet https://www.mouser.ec/datasheet/2/149/FL5150-1008825.pdf
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