Introduction to Electric Circuits

58 DC circuit analysis

Figure 3.32

10~

l t t

5D R31

Ai~l' I :2 l

1 OV

R12

7.5D

15s

R23

1

--~5~ (RE)

Solution

This is called a bridged-T circuit. Note that the resistors R12 , R23 and R31 are

connected in delta. This is shown more clearly in Fig. 3.33 in which the star

equivalent resistors are shown as Ra, Rb and Re. The node labelled S is called the

star point.

Using the delta-star transformation, we have that

Ra = (product of the adjacent delta resistors/sum of the delta connected
resistors)
= 10 x 5/30 = 1.67 f~

Similarly

Rb = 10 X 15/30- 5 f~

ov(

1 10~ 3

7.5fl

IL

5 f~ (RE)

Figure 3.33

And

Rc = 5 x 15/30 = 2.5 f~

The circuit now simplifies to that of Fig. 3.35 via Fig. 3.34.