ELG4139: Rectifiers and Controlled Rectifiers AC to DC Converters Linear Rectifier Consist of: • Transformer: steps ac voltage up or down. • Rectifier Diodes: change ac to “bumpy” dc. • Filter Network: includes capacitors and inductors, smooths out the bumps. • Voltage Regulator: keeps the voltage constant. • Protection: usually a zener diode circuit. Example: Computer Power Supply
Example: Adjustable Motor Speed Drive
Power Supply Specifics: Half Wave Rectifier
Source: ARRL Half-Wave Rectifier
High ripple factor.
Low rectification efficiency.
Low transformer utilization factor. Power Supply Specifics Full Wave Center-Tapped Rectifier
Source: ARRL Power Supply: Full Wave Bridge Rectifier
Source: ARRL Filtering Capacitors are used in power supply filter networks. The capacitors smooth out the rippled AC to DC.
Source: ARRL Rectifier Performance Parameters
Pdc / Pac Rectification Efficiency
2 2 Vac Vrms Vdc 푃푎푐 = 푉푟푚푠퐼푟푚푠
FF Vrms /Vdc Form Factor
V V 2 V 2 V 2 RF ac rms dc rms 1 FF 2 1 Ripple factor 2 Vdc Vdc Vdc Example 1: A half-wave rectifier has a pure resistive load of R Determine (a) The efficiency, (b) Form factor (c) Ripple factor.
1 V V V V V V sin(t) dt m (cos cos(0)) m I dc m dc 2 m 2 dc 0 R R V 1 V m V (V sin t)2 m Irms rms 2 m 2 2 R 0 V V m * m P V * I R dc dc dc 40.53% V V . Pac Vrms * Irms m * m 2 2 R Vm V FF rms 2 1.57 Vdc Vm 2 V RF ac FF 2 1 1.57 2 1 1.211 Vdc Three-Phase Diode Bridge Rectifier Waveforms and Conduction Times of Three-Phase Bridge Rectifier Three-Phase Full-Wave Rectifier
Example 2: A single-phase diode bridge rectifier has a purely resistive load of R=15 ohms and, VS=300 sin 314 t and unity transformer ratio. Determine (a) The efficiency, (b) Form factor, (c) Ripple factor, (d) and, (d) Input power factor. 2V 1 2Vm m V V sint dt 190.956 V Idc 12.7324 A dc m R 0 1/ 2 1 V V V sint2 dt m 212.132 V rms m 2 0 P V I dc dc dc 81.06 % V FF rms 1.11 Pac Vrms Irms Vdc V V 2 V 2 V 2 RF ac rms dc rms 1 FF 2 1 0.482 2 Vdc Vdc Vdc Real Power V I cos Input power factor = S S 1 Apperant Power VS I S Alternative! Controlled Switching Mode
• By using linear regulator, the AC to DC converter is not efficient and of large size and weight! • Using Switching-Mode • High efficiency • Small size and light weight • For high power (density) applications. • Use Power Electronics!
Thyristors and Controlled Rectifiers Controlled Rectifier Circuit
휋 1 푉푝 푉푑푐 = 푉푝푠푖푛휔푡푑휔푡 = 1 + 푐표푠훼 2휋 훼 2휋
휋 1 2 2 1/2 푉푟푚푠 = 푉푝 푠푖푛 휔푡푑휔푡 2휋 훼
1/2 푉 1 푠푖푛2훼 = 푝 휋 − 훼 + 2 휋 2 Example: Consider the following SCR-based variable voltage supply. For RL=240 Ohm, derive the RMS value of the load voltage as a function of the firing angle, and then calculate the load power when the firing angle is 0, /2, and . Full-Wave Rectifiers Using SCR
휋+훼 2 2푉푝 푉푑푐 = 푉푝푠푖푛휔푡푑휔푡 = 푐표푠훼 2휋 훼 휋
휋+훼 2 2 2 1/2 푉푟푚푠 = 푉푝 푠푖푛 휔푡푑휔푡 2휋 훼
푉 = 푝 = 푉 2 푠
With a purely resistive load, SCRs S1 and S2 can conduct from to , and SCRs S3 and S4 can conduct from + to 2.