Hard to get simpler than this:
Just for grins, if you want to play around with the circuit. here's it is using an LTspice shunt regulator and LTspice library parts followed by the circuit list.
Enjoy!
Version 4
SHEET 1 1120 680
WIRE 432 -64 320 -64
WIRE 832 -64 432 -64
WIRE 912 -64 832 -64
WIRE 320 -16 320 -64
WIRE 432 0 432 -64
WIRE 464 0 432 0
WIRE 752 0 720 0
WIRE 752 64 752 0
WIRE 752 64 720 64
WIRE 832 64 832 -64
WIRE 80 112 32 112
WIRE 208 112 160 112
WIRE 320 112 320 64
WIRE 320 112 272 112
WIRE 432 128 432 0
WIRE 464 128 432 128
WIRE 752 128 720 128
WIRE 32 144 32 112
WIRE 320 160 320 112
WIRE 432 192 432 128
WIRE 464 192 432 192
WIRE 752 192 752 128
WIRE 752 192 720 192
WIRE 32 256 32 224
WIRE 320 256 320 224
WIRE 320 256 32 256
WIRE 752 256 752 192
WIRE 752 256 320 256
WIRE 832 256 832 144
WIRE 832 256 752 256
WIRE 32 304 32 256
FLAG 32 304 0
FLAG 912 -64 Vout
SYMBOL voltage 32 128 R0
WINDOW 0 -42 5 Left 2
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value SINE(0 340 50)
SYMBOL res 336 80 R180
WINDOW 0 -38 64 Left 2
WINDOW 3 -50 27 Left 2
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL polcap 304 160 R0
SYMATTR InstName C2
SYMATTR Value 100µ
SYMBOL References\\LT1431 592 96 R0
SYMATTR InstName U2
SYMBOL diode 208 128 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1SR154-600
SYMBOL res 176 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 15k
SYMBOL res 816 48 R0
WINDOW 0 46 46 Left 2
SYMATTR InstName R3
SYMATTR Value 1000
TEXT -80 168 Left 2 ;240AC
TEXT -72 192 Left 2 ;50Hz
TEXT 38 280 Left 2 !.tran 10
TEXT 848 160 Left 2 ;5mA load