Download Does R6 need to be a 1210

R9 and R10
R9 = R10 = 32.4k ohm (value selected for quick startup)
Maximum AC input voltage = 253V
Maximum peak voltage (Vpk) = maximum possible = 253(√2) = 357.8V
Maximum voltage across R9 or R10 = 357.8/2) = 178.9V
Minimum package size to handle the voltage is 1206 (from Vishay D/CRCW e3
datasheet)
Maximum current through R9 and R10 = (357.8/2)/32.4k = 178.9/32.4k = 5.52mA
R9 or R10 Power = (V(pk)/2)2/R = (357.8/2)2/32.3k = 178.92/32.4k = 32k/32.4k = 0.987W
VCC capacitor = 68uF
Time to reach 12V (nominal VCC startup threshold (VCCST))
12V is a small portion of the 357.8V charging VCC, the current charging the VCC
capacitor can be considered as a linear current.
IT = CV
5.52mA(T) = 68uF(12V)
T = 68u(12)/5.52m = 0.816m/5.52m = 148m seconds to charge the VCC capacitor at startup.
= 148m seconds power is dissipated in R9 and R10
Table below from Vishay D/CRCW e3 datasheet. This table is for allowable single pulse wattage
versus time.
I placed red markers to locate the approximate point of operation. The markers are
approximately 148m seconds and approximately 0.987W. The table indicates a 1206 package is
not capable of withstanding the power during startup, so the 1210 package is the recommended
minimum size for R9 and R10.