| Dimensioning of the circuit elements: |
- It is very important to determine the values of resistors R1 and R2 for producing a particular wave shape for known values of C1 and C2
- The total load capacitance can easily be measured if it is not known in advance.
|
| For the circuit in Fig. 28.1(b) the values of R1 and R2 workout as following, |
 (28.10) |
 (28.11) |
- Both these equations contain the time constants 1/α1 and 1/α2, which depend upon the desired wave shape.
- The values of these time constants are worked out for different shapes, T1/T2 , of the output voltage given by equation 28.4 in the table below.
|
T1 /T2 |
Tcr /T2 |
1/α1 |
1/α2 |
(µsec) |
(µsec) |
(µsec) |
(µsec) |
1.2 / 5 |
- |
3.48 |
0.80 |
1.2 / 50 |
- |
68.2 |
0.405 |
1.2 / 200 |
- |
284 |
0.381 |
250/2500 |
- |
2877 |
104 |
| - |
250/2500 |
3155 |
62.5 |
|
- The nominal values of T1 and T2 are difficult to achieve in practice, as even for fixed value of C1, the load C2 may vary for different loads. The exact values for R1 and R2 according to eqns. (28.10) and (28.11) are in general not available. These resistors have to be dimensioned for the rated high voltage of the stage.
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