Power electronics introduction
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| buck | chuyển đổi降压 (buck) |
| boost | chuyển đổi升压 (boost) |
| continuous conduction | continuous conduction |
Balance the volt-seconds
- Steady state forces the inductor volt-second sum to zero: $(V_{in} - V_{out})DT = V_{out}(1-D)T$, so $V_{out} = D V_{in}$ (buck) or $V_{in}/(1-D)$ (boost) — independent of L, C and load in continuous conduction.
12 V → 5 V at 2 A, 100 kHz, L = 100 µH: $D = 0.417$, $\Delta I_{L} = 0.29$ A (15%), CCM holds ($0.15 < 2$ A), and 220 µF caps it at $\Delta V = 1.7$ mV.
{exercise:uni-ee0971-buck}
A buck converter from 12 V to 5 V at 100 kHz with L = 100 µH has a duty cycle and ripple of about —
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
D = Vout/Vin = 5/12 = 0.417; ΔI = Vout(1−D)/(Lf) = 5×0.583/10 = 0.29 A. D = 0.583 is the OFF share, not the duty.
The buck above (ΔI/2 = 0.146 A) is unloaded until its load current falls to 0.10 A. Then —
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
Below the boundary current ΔI/2 the inductor empties each cycle; the simple volt-second result no longer holds and the output drifts high.
The boost and its bigger capacitors
- 12 V → 24 V at 1.5 A: $D = 0.5$, input current 3 A (power conserved, current is not), $\Delta I_{L} = 0.6$ A.
- The output capacitor sees pulsed current during $(1-D)$ of each period — RMS ripple, not average, sizes boost capacitors.
{exercise:uni-ee0972-boost}
A boost converter from 12 V to 24 V delivering 1.5 A (ideal) draws an input current of —
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
Power is conserved: 24 × 1.5 = 36 W over 12 V = 3 A. Current trades against voltage; only power is invariant.