What are the advantages or disadvantages of half versus full wave rectifiers?
A full wave bridge provides more DC power given the same input voltage. The AddMe II includes a 24VDC excitation output, which is essentially a DC power supply. The AddMe III family does not include this output and cannot support such an output because these products use half wave rectifiers. Under load, the unregulated DC from the half wave rectifier falls too low to sustain a 24VDC output without very large filter capacitors. The bulk of filter capacitors necessary to sustain 24VDC output from 24VAC input using a half wave rectifier would occupy nearly half the available circuit board space in the product. It’s not impossible, just impractical. The disadvantage of the full wave bridge is that neither side of the AC coming into the rectifier can be grounded. Since grounded AC is common in HVAC applications, most of the newer Control Solutions products are using half wave rectifiers to avoid the grounding problem. The cost of doing so is giving up the 24VDC excitation output.
