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calculating current requirement of LDO and switcher

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gary36

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Hi
1. An 12V to 5V LDO is rated for 1A. What should be the current sourcing capability for 12V input source? Can it be same as 1A ?
2. An AC-DC converter is rated as follows Input side: 220 / 118mA, output is +/-12V/0.625A, 15W, 80% efficiency. From direct calculation , input power = 220*.118=25.96W and output power= 15W as mentioned, then efficiency must be 15/25*100= 60%, how is it 80%?
 

1. 12V to 5V @ 1A LDO has source current 1A +Quiescent current(in few mA/uA) of LDO.
2. I am not expert on this, But you can't calculate input power directly 220*0.118, because it is AC not DC.many links are in google.
 

Hi,

This may be wrong but if you multiply +-12V i.e. 24V (AC) * 1.414 = 33.936V. 33.936V (DC) * 0.625A = 21.21W. 21.21W/25.96W = 0.817 * 100 = ~80%.
 

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