Semiconverter Power Rectifier (Power Bridge)

The conduction time of the SCRs in the power bridge determines the amount of output current supplied to

the generator exciter field. Conduction time is controlled by the timing of gating pulses from the firing circuits.

The greater the conduction time of the SCRs, the greater the output current. The less the conduction time,

the less the output current.

Firing Circuit

The circuit compares a dc signal representative of the SCR output with a reference input established by the

manual adjust control (R5). Gating pulses to the power bridge are developed as a result of the comparison

of the two inputs. As R5 is adjusted to demand a higher or lower nominal generator output, the firing circuits

determine whether the gating pulses need to be applied earlier or later in the SCR firing cycle to establish

the new operating level. The power bridge responds by providing the correct output to the generator field.

When the auto / manual mode switch is in manual, R5 (essentially a manual voltage control) and the firing

circuits function independently of the rest of the exciter-regulator and the excitation system does not

regulate the system ac voltage. (Refer to Section 3. Controls)