The desired output specs are 15VDC, 0.6A constant current load.

Assuming my Regulator cct has a 4V Drop out, the minumum DC input shall be no less than 19VDC

My planned Bill of Materials are:

18V 25VA Transformer

4x 1N5401 Diodes (3A) as a Full wave bridge rectifier (FWBR)

1x 63VDC 2200uF Capacitor

In Section 8 of the Nat. Sem. Handbook, it says as a guide, Secondary Transformer current is 1.8 times the Load current for a FWBR + Capacitor filter.

Therefore my Secondary current is 0.6*1.8 =

__1.08Arms.__

Circuit to be driven from a 18Vrms Transformer. Calculated an approx

__1.151Ohm__ESR (calculated from the Primary DC Resistance, the turns ratio and Secondary DC Resistance)

1.08Arms * 1.151 ESR =

__1.24Vrms__Drop (Transformer spec doesnt quote the Inductance so cannot calc Xl or the Z, so ESR is closest i can do)

Diode currents should be assumed at 3 times the DC load current, so

__1.8Aavg__. 1N5401 is rated for 3A continuous, 100V Reverse rating. Should be suitable.

The Handbook also states that the RMS Capacitor current should be assumed 2-3 times the DC Load. in this case

__1.8Arms__Ripple Current.

I have chosen a DC rating greater than 2x the Peak No load voltage of the transformer. I.e. 63VDC

With a bit of hit/miss i think a 2200uF Capacitor is suitable, based on the ripple voltage, calculated from Art of Electronics, Horowitz & Hill, Full wave bridge rectifier ripple voltage is;

Vripple (pk to pk) = Iload / 2*F*C

= 0.6 / 2 * 50 * 2200uF

=

__2.727__V pk 2 pk.

Then to add up voltages and to calculate the minimum Secondary RMS voltage required if the 230VAC Transformer was supplied down to 220VAC.

Vf = 0.8V (worst case scenario)

FWBR Effeciency = 92%

Nominal Line Voltage 230, min 220

Vt = Transformer ESR drop (1.24Vrms)

Vt + [(Vout + Vdrop + 2*Vf + Vrip) 0.92 ] * (230/220) * 1/SQRT(2)= (from National Semi Handbook)

1.24 + [(15 + 4 + (2*0.8) + 2.727) *0.92] * (230/220) * (1/SQRT(2)) = 17.102Vrms minimum (so 18Vrms Transformer should be fine)

Does this all look sensible/logical? Any thoughts/comments would be greatly appreciated.