issues of using NCP1010(current model regulator) after voltage dropping capacitor

[Bro_T]

in my AC/DC power supply circuit, I first use a voltage dropping capacitor to reduce incoming voltage. For the load stability, then I add the NCP1010(current model regulator) circuit as the 2nd level. Here is the findings:
1. Voltage dropping circuit itself is ok. Without the NCP1010 circuit it can get ~180v on the resistance(15K), ~2W.
2. But after adding the NCP1010 circuit, the voltage on the resistance(15k) is only ~50v. Accordingly the final output is far below the expected 5v. Total consume is <<2W.


Anyone could tell me what's the problem. Why I can' t get the final 5v with this circuit?

 

[BradtheRad]

2. But after adding the NCP1010 circuit, the voltage on the resistance(15k) is only ~50v. Accordingly the final output is far below the expected 5v. Total consume is <<2W.

Output voltage drops, but not due to the device robbing power? Instead it causes a decrease in power? Not sure what to make of this.

The NCP1010 is a switching regulator IC. Did you rule out using a zener diode?

Just to see how this would work with 5.1 zener regulation...
A simulation showing suitable values to power a 51 ohm load. (Mains is 120 VAC.)



C1 needs to be 2.5 uF or more, to carry sufficient amperes.

 

[Bro_T]

thx. Why i use the NCP as the 2nd level, that is my loading is not fixed(0w-1w, 0-200ma) which may beyond the the zener capacity. and Also i need a isolated circuit. i use the RC voltage dropping to reduce the 2nd level input voltage which will bring me a smaller transforme.
i am just curious why with NCP, the power dropped so much.

 

[Bro_T]

thx BradtheRad. why i don't use the zener, that is my loading is not fixed swinging from 0 to 200mA. and also i need the isolate the AC and final output. the voltage dropping circuit could help for a smaller transformer.
i'm just curious why with the NCP, the power dropped so much.
thx.