Page 328 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Another arrangement of this bridge is shown in Fig. It uses four SCRs. Here four SCRs i.e.
SCR , SCR , SCR and SCR are used to form the rectifier bridge. In the positive half-cycle
1
2
4
3
of the a.c. input, conduct and in the negative half cycle the other two SCRs i.e. SCR and
2
SCR conduct. So, d.c. output is available in both the halves. Hence, for the positive half cycle, SCR and SCR
1
3
4
are responsible for control, while for negative half cycle SCR and SCR are responsible. Therefore, each arm of
2
3
the bridge is involved in both the halves of the a.c. input and hence it is called fully controlled bridge.
Three- phase Full-wave Half controlled bridge
The circuit diagram of three-phase full-wave half-controlled bridge is shown in Fig.
This configuration uses in all the three SCR’s (S , S , S ) and 3 diodes (D , D , D ), with one pair of SCR and
1
3
3
2
2
1
diode per phase. In every phase output is available in both the halves of the a.c. input but only one control device
is used in both the half cycles and therefore it is called a half controlled full-wave bridge. Diode D is used for
4
freewheeling purposes.

Three phase Full wave Fully Controlled Bridge
In all six SCR`s have been used with a pair per phase to give a full wave fully controlled output.

Diode D is freewheeling diode .

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CITS : E & H - Electronics Mechanic - Lesson 199 - 204