Brownsburg Electronik inc.

aaHOW TO DETERMINE THE RIGHT SIZE OF TRANSFORMER aaWHEN USED WITH A RECTIFIER CIRCUIT?
The A.C power (VA) required to supply a D.C load through a rectifier circuit is higher than the D.C. power going through the load. The A.C. power rating will vary with the type of rectifier circuit and the type of load. We are giving you formulas that are to be used as a guide to help you determine the right size of transformer. We have chosen the most common rectifier circuits and loads.
HALF WAVE Resistive Load		HALF WAVE Capacitive Load

VAC = 2.26 VDC + VDROP lAC = 1.57 lDC VAAC = 3.55 ( Watts + 0.44 lDC VDROP)		VAC = VDC + VDROP lAC = 2.30 lDC VAAC =2.30 ( Watts + lDC VDROP)

FULL WAVE CT Resistive Load		FULL WAVE CT Capacitive Load

VAC = 2.26 VDC + VDROP lAC = 0.79 lDC VAAC = 1.79 ( Watts + 0.44 lDC VDROP)		VAC = 1.70 VDC + VDROP lAC = 1.15 lDC VAAC = 1.96 ( Watts + 0.59 lDC VDROP)

FULL WAVE BRIDGE Resistive Load		FULL WAVE BRIDGE Capacitive Load

VAC = 1.13 VDC + 2 VDROP lAC = 1.11 lDC VAAC = 1.26 ( Watts + 1.76 lDC VDROP)		VAC = 0.85 VDC + 2VDROP lAC = 1.65 lDC VAAC = 1.41 ( Watts + 2.34 lDC VDROP)

Where:

VAC = A.C. rms voltage (coming out of the transformer)
VDC =D.C rms voltage (coming out of the diodes)
VDROP = D.C. rms voltage across a diode (typically 1 Volt)
IAC = A.C. rms current (coming out of the transformer)
IDC =D.C rms current (coming out of the diodes)
VAAC = VAC * IAC (This value characterizes the size of the transformer)
Watts = VDC *IDC (This value is the power in a resistive load)