Blocking Losses: Due to leakage current during OFF-state, usually negligible.

Thermal Management: Junction temperature ($T_j$) must be kept below maximum.

$P_D = \frac{T_j - T_A}{R_{\theta JA}} = \frac{T_j - T_C}{R_{\theta JC}}$ (where $P_D$ is total power dissipated).
$R_{\theta JA} = R_{\theta JC} + R_{\theta CS} + R_{\theta SA}$ (Junction-to-Ambient thermal resistance).

Natural (Line) Commutation: Occurs in AC circuits when AC supply voltage reverses, forcing anode current below $I_H$. No external components needed.
Forced Commutation: Required for DC circuits or when natural commutation is not possible. External circuit forces anode current to zero.
- Class A (Load Commutation): Resonant LC circuit in series with SCR/load.
```
SCR -- L -- C -- Load
```
- Class B (Resonant-Pulse Commutation): Resonant LC circuit in parallel with SCR.
```
SCR -- Load
|      |
L      C
```
- Class C (Complementary Commutation): Two SCRs in series, turning one ON commutates the other.
- Class D (Auxiliary Commutation): Auxiliary SCR and LC circuit used to commutate main SCR.
- Class E (External Pulse Commutation): External pulse source to reverse-bias SCR.

Convert AC to variable DC by controlling firing angle ($\alpha$).

Half-wave Controlled Rectifier (R-Load):
- Average Output Voltage: $V_{dc} = \frac{V_m}{2\pi}(1 + \cos\alpha)$
- RMS Output Voltage: $V_{o,rms} = \frac{V_m}{2}\sqrt{1 - \frac{\alpha}{\pi} + \frac{\sin(2\alpha)}{2\pi}}$
Full-wave Bridge Controlled Rectifier (R-Load):
- Average Output Voltage: $V_{dc} = \frac{2V_m}{\pi}\cos\alpha$
- RMS Output Voltage: $V_{o,rms} = \frac{V_m}{\sqrt{2}}\sqrt{1 - \frac{\alpha}{\pi} + \frac{\sin(2\alpha)}{2\pi}}$
Full-wave Bridge Controlled Rectifier (RL-Load, Continuous Conduction): Assumes large inductance.
- Average Output Voltage: $V_{dc} = \frac{2V_m}{\pi}\cos\alpha$ (same as R-load)
- Output current is smoother. Current may flow even when instantaneous source voltage is negative.

Three-Phase Half-wave Converter (R-Load): (Not common due to DC current in AC source)
- Average Output Voltage: $V_{dc} = \frac{3V_{mL}}{2\pi}(1 + \cos\alpha)$
- $V_{mL}$ is peak line-to-neutral voltage.
Three-Phase Full Converter (Bridge, R/RL-Load):
- Average Output Voltage: $V_{dc} = \frac{3V_{mLL}}{\pi}\cos\alpha$ (where $V_{mLL}$ is peak line-to-line voltage)
- Can operate as an inverter for $\alpha > 90^\circ$ (requires DC source and grid connection).

Firing Angle ($\alpha$): Delay from natural commutation point. $0 \le \alpha \le \pi$.
Load Types: R, RL, RLE (e.g., DC motor with back EMF $E_b$).
Performance Parameters:
- Ripple Factor (RF): Measures AC content in DC output. $RF = \frac{V_{o,ac}}{V_{o,dc}} = \frac{\sqrt{V_{o,rms}^2 - V_{o,dc}^2}}{V_{o,dc}}$.
- Efficiency ($\eta$): $\eta = \frac{P_{out,dc}}{P_{in,ac}}$.
- Input Power Factor (PF): $PF = \fra