Power Electronics Circuits
For an ideal step-up chopper (boost converter) with an input voltage of 5 V and a switch duty cycle of 0.6, which of the following is the output voltage in continuous conduction mode?
- A3 V
- B8 V
- C12.5 V
Show answer and explanation
Answer: C. 12.5 V
The output voltage of an ideal boost converter is Vout = Vin/(1 − D). 5 V ÷ (1 − 0.6) = 5 ÷ 0.4 = 12.5 V. The formula follows from the balance of volt-seconds across the inductor, with Vin applied while the switch is on and (Vout − Vin) while it is off: Vin × D = (Vout − Vin) × (1 − D). The 3 V of D × Vin is the formula of the buck converter.
- A. This is D × Vin, the buck-converter formula. The output of a boost converter is higher than its input.
- B. This is (1 + D) × Vin, which is not the boost-converter formula.
- C. Correct. 5 ÷ (1 − 0.6) = 12.5 V.