how to calculate the hold up capacitor in power supply......

[get2kamal]

capacitor holdup energy

hai,,.,


how to calculate the hold up capacitor in swich mode power supply ,,, it is a AC/DC converter min AC line voltage is 150 v,,, o/p volage 35 ,current 3.5 A,, requir hold up time 20 ms......

regards
kamal

 

[shaz]

Re: how to calculate the hold up capacitor in power supply..

wht is the application ? so that i can answer in better way

 

[Davood Amerion]

input voltage 150V will consume about 0.6-0.7 amp.
for 220-240V input, current is lower (about 0.5-0.6A)
if we assume current consumption are 0.7A, and voltage change (peak value) 300-210=90V
then C=(i/V)*t
then C will be :
C = (0.7/90) 20(ms)= 155uF
you can use 220uF/400V

Note: all above values are approximate.

regards,
Davood

 

[get2kamal]

Re: how to calculate the hold up capacitor in power supply..

thanks for your reply davood,.,.,.,

but the exact method is(i got it from one application note),,,,,,

switch off the smps @ 150 v ac (not @ 230 vac) o/p voltage should be with in regulation for 20ms......
c hold up ≥ (2 × pin × t hold up)÷η×((v nominal)² - (v drop out)²)
because energy stored in the capacitor = ½cv²=p×t (rearrange this equation) c=(2×p×t)÷v²