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Diode Circuits: Applications

Diode Circuits: Applications. Applications – Rectifier Circuits. Half-Wave Rectifier Circuits. Applications – Rectifier Circuits. Battery-Charging Circuit. Half-Wave Rectifier with Smoothing Capacitor. Large Capacitance. i=dq/dt or Q = I L T Q = V r C then

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Diode Circuits: Applications

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  1. Diode Circuits:Applications

  2. Applications – Rectifier Circuits Half-Wave Rectifier Circuits

  3. Applications – Rectifier Circuits Battery-Charging Circuit

  4. Half-Wave Rectifier with Smoothing Capacitor Large Capacitance i=dq/dt or Q = IL T Q = Vr C then C ~ (ILT) / Vr

  5. Half-Wave Rectifier with Smoothing Capacitor Vr Peak-to-peak riple voltage Large Capacitance Start i=dq/dt or Q = IL T Q = Vr C then C ~ (ILT) / Vr typically :VL ~V m- (Vr /2) Forward bias charge cycle Reverse bias discharge cycle

  6. Full-Wave rectifier Circuits The sources are out of phase

  7. Wave Shaping Circuits Clipper Circuits Batteries replaced by Zener diodes Review examples: 10.14 10.15 10.16 10.17 10.18

  8. + 600 mV - 600 mV Iflow Above 600 mV Iflow below 600 mV Half-Wave Limiter Circuits Current flows thru the resistor until +600 mV is reached, then flows thru the Diode. The plateau is representative of the voltage drop of the diode while it is conducting. Voltage divider

  9. Linear Small Signal Equivalent Circuits (1) When considering electronic circuits in which dc supply voltages are used to bias a nonlinear devices at their operating points and a small ac signal is injected into the circuit to find circuit response: • Split the analysis of the circuit into two parts: • analyze the dc circuit to find the operating point • consider the small ac signal

  10. Linear Small Signal Equivalent Circuits (1) Since virtually any nonlinear ch-tic is approximately linear (straight) if we consider a sufficiently small segment THEN We can find a linear small-signal equivalent circuit for the nonlinear device to use in the ac analysis The small signal diode circuit can be substituted by a single equivalent resistor.

  11. Linear Small Signal Equivalent Circuits (2) dc supply voltage results in operation at Q An ac signal is injected into the circuit and swings the instantaneous point of operation slightly above and below the Q point For small changes DiD –the small change in diode current from the Q-point DvD –the small change in diode voltage from the Q-point (diD/dvD) – the slope of the diode ch-tic evaluated at the point Q

  12. Linear Small Signal Equivalent Circuits (2) dc supply voltage results in operation at Q An ac signal is injected into the circuit and swings the instantaneous point of operation slightly above and below the Q point For small changes Dynamic resistance of the diode DiD –the small change in diode current from the Q-point DvD –the small change in diode voltage from the Q-point (diD/dvD) – the slope of the diode ch-tic evaluated at the point Q

  13. Linear Small Signal Equivalent Circuits (3) From small signal diode analysis Differentiating the Shockley eq. … and following the math on p.452 we can write that dynamic resistance of the diode is where

  14. Example - Voltage-Controlled Attenuator Find the operating point and perform the small signal analysis to obtain the small signal voltage gain DC control signal C1, C2 – small or large ? C in dc circuit – open circuit C in ac circuit –short circuit

  15. Example - Voltage-Controlled Attenuator DC control signal Dc circuit for Q point (IDQ, VDQ) Compute at the Q point (IDQ, VDQ)

  16. Example - Voltage-Controlled Attenuator The dc voltage source is equivalent to a short circuit for ac signals. Voltage gain

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