Page 188 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

POWER ELECTRONICS, RECTIFIERS, AND PULSE-WIDTH MODULATION INVERTERS

POWER ELECTRONICS, RECTIFIERS, AND INVERTERS 9.15

FIGURE 9.21 (a) Using a pulse generator to directly trigger an SCR. (b) Coupling a pulse generator to
an SCR through a transformer. (c) Connecting a pulse generator to an SCR through a transistor amplifier to
increase the strength of the pulse.

FIGURE 9.22 A relaxation oscil-
lator using a DIAC instead of a
PNPN diode.

PULSE SYNCHRONIZATION
The triggering pulse should be applied to the controlling SCRs at the same point in each ac
cycle. This is normally done by synchronizing the pulse circuit to the ac power line sup-
plying the SCRs. This is done by making the power supply to the triggering circuit the same
as the power supply to the SCRs.

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