Cct Models for semiconductor diodes Diode Models Large
- Slides: 21
Cct. Models for semiconductor diodes Diode Models Large Signal Ideal Diode Small Signal Offset Diode Piecewise Linear
Offset Diode Model q Internal resistance =0 q Cutoff frequency (c)>0 (Vγ=0. 6 volts for Silicon) q Reverse current (Is) =0 q Can be modeled as Ideal diode in series with Vγ
I-V characteristic curve q Offset diode accounts for the offset voltage (better approximation). q If VD < Vγ it will be OFF (open circuit in series with Vγ. q If VD> Vγ it will be ON (short circuit series with Vγ).
Example 1 Given offset diode with Vg = 0. 7 V, Calculate ID. we assume it is ON and then check current direction if it is consistent. By inspection it is clear that current is consistent with our assumption
Example (cont. ) q Try solving assuming that diode is off. q Note that offset diode voltage is not similar to the open cct. voltage.
Example 2 If VB = 2 V; R 1 = 1 k; R 2 = 0. 5 K ; Vγ = 0. 6 V. Determine Minimum value of V 1 so D 1 conducts. Sol: we assume diode OFF.
Cct. Models for semiconductor diodes Diode Models Large Signal Ideal Diode Small Signal Offset Diode Piecewise Linear
Large Signal Vs. Small signal Models q In small signal model, the exact I-V char. Curve is used to determine diode voltage and current it is used to determine accurate operating point of the diode. q Large signal models use approximating I-V char. Curve and thus approximate results of diode voltage and current.
Small Signal Model q No approximation is used. q Diode cannot be replaced q q with linear element (open or short). We need to deal with the non-linear properties of the diode. KVL, KCL can be applied Nodal and Mesh analysis cannot be used. Superposition only deals with Linear circuit elements!!
The Operating point of the Diode q The operating point (or Q-point) is the point that determines the exact value of diode voltage and diode current.
Load-Line Analysis of Diode Circuits
Example 1 - Load-Line Analysis
Example 2 - Load-Line Analysis
Load-Line Analysis of Complex Circuits What if we have more than one source and one load ? ? Use the Thevenin Equivalent
Example 3
Example 3 (cont. ) q The Q point (Operation point) is the solution of the system. (IDQ, VDQ)
Example 4 q Determine the operating point of the diode shown in the following circuit. q The I-V char. Curve is given below.
Example 4 (cont. )
Cct. Models for semiconductor diodes Diode Models Large Signal Ideal Diode Small Signal Offset Diode Piecewise Linear
Piecewise linear Diode Model q For this model we assume the following: Cutoff frequency >0 Internal resistance (r. D) >0 (but constant!!) Reverse current =0. The approximation mainly in the value of the internal resistance.
Piecewise-Linear Diode Models q Now, diode voltage is the sum of resistance voltage and cutoff frequency voltage.
- Characteristics of a semiconductor diode
- Diode germanium vs silicon
- Diode conclusion
- Schottky diode definition
- Tvs vs schottky diode
- Current equation of bjt
- Ideal diode model examples
- Diode small signal model
- Full wave rectifier 4 diodes
- Power diodes types
- Zener diode exhibit
- Circuit analysis with diodes
- Diodes
- Diode law
- Et 212
- Special purpose diodes
- Special purpose diodes
- Termistor simbol
- Solid state diode definition
- Advantages of zener diode
- What are diodes made out of
- Introduction to diodes