Input Current Calculation

The following describes how to calculate the input current of a power supply with a capacitive input.

The following formula applies:

Iin = Pout/(E*PF*Vin)

Where:

Iin	=	Input Current (A RMS)	Pout	=	Output Power (W)	=	Sum of product of output voltages (VDC) and their corresponding load currents (ADC).
E	=	Efficiency	=	Ratio of Pout to Pin; can be obtained from published specs, as well.
Pin	=	Input Power (W)
Vin	=	Input Voltage (V RMS)
PF	=	Power Factor; Typically 0.7 for switchers, 0.8 for linears; Actual value depends on source impedance.

To obtain maximum Iin, use the following formula:

Iin, max = Pout, max/(Emin * PFmin * Vin, min)

Where:

Iin, max	=	Maximum Input Current (A RMS)
Pout, max	=	Maximum Rated Output Power (W)
Emin	=	Minimum Efficiency	=	Ratio of Pout, max to Pin
Vin, min	=	Minimum Input Voltage (V RMS)
PFmin	=	Minimum Power Factor; typically 0.6 for switchers, l7 for linears; actual value depends on source impedance.

Example:

Model: SPM5A2B5D1K,
5V @ 150A, -12V @ 10A, -12V @ 10A, 24V @ 5A

Pout	=	5(150) +12(10+12(10) + 24(5)	=	1230W
E	=	0.7
Vin	=	90VAC
PF	=	0.7
===>Iin	=	27.9 A RMS

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