Chapter Summary

Chapter recap — Power Electronics and its Applications

Power semiconductor devices

• Power electronics uses solid-state devices as fast, loss-free switches to control and convert electric power. An ideal power device blocks a large voltage, carries a large current, has a near-zero on-state drop and zero off-state leakage, and switches instantly.
• The power diode uses a lightly doped n- drift (epitaxial) layer between p+ and n+ layers for reverse blocking; double injection causes conductivity modulation, keeping the forward drop low. Its forward drop is $V_{AK} = V_j + R_{ON} I_F$, and its V–I curve follows the Shockley equation $I = I_S\left[e^{qV/kT} - 1\right]$. Reverse behaviour is either non-punch-through or punch-through.
• The power BJT is a current-controlled device working in cut-off, active and saturation regions.
• The SCR is a four-layer, three-terminal pnpn device, understood through the two-transistor analogy. It is turned on by a gate pulse but not turned off by the gate. Gate-open anode current is $I_A = I_{co}/[1-(\alpha_1+\alpha_2)]$; with gate current, $I_A = (\alpha_2 I_G + I_{co})/[1-(\alpha_1+\alpha_2)]$. Key points on its characteristic are the break-over voltage $V_{BRF}$, holding voltage $V_H$, latching current $I_L$ and holding current $I_H$ ($I_H < I_L$).
• The TRIAC is a bidirectional device (MT1, MT2, gate) with symmetric characteristics and four triggering modes, used for AC power control.
• The power MOSFET is a voltage-controlled device (drain, source, insulated gate) with cut-off, ohmic and active modes.
• The IGBT combines a MOSFET input (high input impedance) with a BJT output (low on-resistance); terminals C, G, E.

Applications

• Power devices act as static switches and are wired into four converters: rectifier (AC–DC), AC voltage controller (AC–AC), chopper (DC–DC) and inverter (DC–AC).
• SCR rectifiers with RC triggering control the output by delaying the firing angle $\alpha$: half-wave $V_{dc} = \dfrac{V_m}{2\pi}[1+\cos\alpha]$; full-wave $V_{dc} = \dfrac{V_m}{\pi}[1+\cos\alpha]$. …