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Chapter # 4

Chapter # 4. Basic electronics Lecture 4. V P. V in. V P. V out. The half-wave rectifier. Ideal: V P(in) = V P(out). V in. V out. Half-wave rectifier. The dc value of the output is the average value. V dc = V P / p f out = f in

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Chapter # 4

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  1. Chapter # 4 Basic electronics Lecture 4

  2. VP Vin VP Vout The half-wave rectifier Ideal: VP(in) = VP(out) Vin Vout

  3. Half-wave rectifier • The dc value of the output is the average value. • Vdc = VP/p • fout = fin • Second approximation: VP(out) = VP(in) - 0.7 V

  4. Transformer review • When the turns ratio (N1/N2) is greater than 1, the primary voltage is stepped down. • When the turns ratio is less than 1, the primary voltage is stepped up. • Dotted ends have the same instantaneous phase. • Full-wave rectifiers require a winding with a center tap.

  5. Vin Vout The full-wave rectifier C.T. Vout

  6. Full-wave rectifier • The dc value of the output is the average value. • Vdc = 2VP/p • fout = 2fin • The input to each diode is half the secondary voltage. • Second approximation: VP(out) = VP(in) - 0.7 V

  7. Vin Vout The bridge rectifier Vout

  8. Bridge rectifier • The dc value of the output is the average value. • Vdc = 2VP/p • fout = 2fin • Second approximation: VP(out) = VP(in) - 1.4 V

  9. XC Vout@ Vin XL The choke-input filter L C Vout RL Vin When XL >> XC:

  10. Discharge VP Charge I VR = fC Where VR is the peak-to-peak ripple voltage The capacitor-input filter + 0 -

  11. Dc output voltage drops when load current increases • Ac line regulation can have an effect • Bulk resistance of rectifiers causes a voltage drop • Resistance of transformer windings causes a voltage drop • Ac ripple increases and average dc decreases

  12. Diode ratings • Half-wave rectifier with capacitor-input filter: PIV = 2VP Idiode = Idc • Full-wave rectifier with capacitor-input filter: PIV = VP Idiode = Idc • Bridge rectifier with capacitor-input filter: PIV = VP Idiode = 0.5Idc

  13. Bridge supply troubleshooting • No output - - blown fuse, two or more diodes open, load shorted • Low output/extra ripple - - bad filter, open diode, shorted winding, overload • Full-wave signal at output - - open filter capacitor • Half-wave ripple frequency - - open diode

  14. Positive clipper RS 0.7 V RL Vin Vout

  15. Negative clipper RS RL Vin Vout -0.7 V

  16. Positive clamper C RL Vout -0.7 V Stiff clamper: RLC > 100T

  17. Negative clamper C 0.7 V RL Vout Stiff clamper: RLC > 100T

  18. VP D2 C1 D1 2VP C2 Half-wave voltage doubler

  19. VP VP Full-wave voltage doubler 2VP

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