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A single ended class A transformer coupled amplifier is to deliver a power of 50 mW to the load in the secondary. Given efficiency of transformer is 70%, the transistor chosen should have a power dissipation capability PT given approximately by:
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- 35 mW
- 70 mW
- 100 mW
- 140 mW
Correct Option: A
Given Po (ac) = 50 mW
efficiency of transformer = 70%
output power deliver to the load = efficiency of transformer × Po (ac)
= 0.70 × 50 = 35 mW
Now,
Efficiency of class-A transformer coupled amplifier
| ⇒ 50% = | ||
| Pi(dc) |
| ⇒ 0.5 = | ||
| PD + 35 mW |
(∴ Pi (dc) = PD + Po (ac))
⇒ 0.5 PD + 35 × 0.5 = 35
⇒ 0.5 PD = 17.5 mW
| ⇒ PD = | = 35 mW | |
| 0·5 |
Hence alternative (A) is the correct choice.
