- 2069 Chaitra · 3+3 marks
Transformer coupled push-pull efficiency, 20 V supply
Short answer
Efficiency of transformer-coupled class B push-pull amplifier is η = (π/4)(Vp/VCC). For VCC=20 V: (i) with VP=20 V, η=78.5%; (ii) with VP=16 V, η=62.8%.
Calculate the efficiency of transformer coupled push pull Power Amplifier for a supply voltage of 20V and output of (i) VP = 20V (ii) VP = 16V.
Given: Transformer-coupled class B push-pull, VCC = 20 V. Efficiency is
η = (π/4)(VP/VCC) × 100 %
where VP is the peak output (collector) voltage swing across one half of the primary. Derivation: Po = VP²/(2R'L), Pi = VCC · 2VP/(π R'L), so Po/Pi = (π/4)(VP/VCC), independent of the load resistance.
(i) VP = 20 V
η = 0.7854 × 20/20 = 0.7854 → 78.5 %
This is the maximum possible value, since VP = VCC.
(ii) VP = 16 V
η = 0.7854 × 16/20 = 0.7854 × 0.8 = 0.6283 → 62.8 %
| VP | VP/VCC | η |
|---|---|---|
| 20 V | 1.0 | 78.5 % |
| 16 V | 0.8 | 62.8 % |
Answer: (i) 78.5 %, (ii) 62.8 %.
✓ Answer checked by Claude Opus 5.5 (high effort)
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