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 C ~ (I L T) / V r

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

Full-Wave rectifier Circuits The sources are out of phase

Wave Shaping Circuits Clipper Circuits Batteries replaced by Zener diodes Review examples:

600 mV mV I 600 mV I flow below 600 mV I 600 mV I flow Above 600 mV 600 mV 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

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: (a)analyze the dc circuit to find the operating point (b)consider the small ac signal

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.

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  i D –the small change in diode current from the Q-point  v D –the small change in diode voltage from the Q-point (di D /dv D ) – the slope of the diode ch-tic evaluated at the point Q

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  i D –the small change in diode current from the Q-point  v D –the small change in diode voltage from the Q-point (di D /dv D ) – the slope of the diode ch-tic evaluated at the point Q Dynamic resistance of the diode

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 Linear Small Signal Equivalent Circuits (3) where

Example - Voltage-Controlled Attenuator DC control signal C 1, C 2 – small or large ? C in dc circuit – open circuit C in ac circuit –short circuit Find the operating point and perform the small signal analysis to obtain the small signal voltage gain

Example - Voltage-Controlled Attenuator DC control signal Dc circuit for Q point (I DQ, V DQ ) Compute at the Q point (I DQ, V DQ )

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