Manual

12 | SAMLEX AMERICA INC.
SECTION 4 | Powering Direct / Embedded Switch
Mode Power Supplies (SMPS)





inrush current drawn by the power supply as the input capacitors are charged (The ca-

current at turn-on is several to tens of times larger than the rated RMS input current

waveforms is given in Fig. 4.1. It will be seen that the initial input current pulse just after




in Fig 4.2 above. The steady state input current of SMPS is a train of non-linear pulses
instead of a sinusoidal wave. These pulses are two to four milliseconds duration each

around three times the RMS value of the input current:


-

the input to the power supply. The cold resistance limits the input current as the input



current event.

Hence, it is recommended
that for purposes of sizing the inverter, the continuous power of the inverter should be
> 3 times the continuous rated power of the SMPS. For example, an SMPS rated at
100 Watts should be powered from an inverter that has continuous power of
> 300 Watts.