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Microelectronics Circuit Analysis and Design. Donald A. Neamen Chapter 2 Diode Circuits. In this chapter, we will:.

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Microelectronics Circuit Analysis and Design

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Donald A. Neamen

Chapter 2

Diode Circuits

### In this chapter, we will:

• Determine the operation and characteristics of diode rectifier circuits, which is the first stage of the process of converting an ac signal into a dc signal in the electronic power supply.

• Apply the characteristics of the Zener diode to a Zener diode voltage regulator circuit.

• Apply the nonlinear characteristics of diodes to create waveshaping circuits known as clippers and clampers.

• Examine the techniques used to analyze circuits that contain more than one diode.

• Understand the operation and characteristics of specialized photodiode and light-emitting diode circuits.

### Block Diagram for ac to dc Converter

The diode rectifier, filter, and voltage regulator are diode circuits.

### Problem-Solving Technique: Diode Circuits

• Determine the input voltage condition such that the diode is conducting (on).

• Find the output signal for this condition.

• Determine the input voltage such that the diode is not conducting (off).

• Find the output signal for this condition.

### Half-Wave Rectifier

Voltage Transfer Characteristics

### Signals of Half Wave Rectifier

Input voltage

Output voltage

Diode voltage

Load line when vS is at its maximum forward voltage.

Load line when vS is at its most negative value.

As vS varies with time, the load line also changes, which changes the Q-point (vD and iD) of the diode.

### Full-Wave Rectifier

Voltage transfer characteristics

Input and output waveforms

### Full-Wave Bridge Rectifier

When vS is positive, D1 and D2 are turned on (a). When vS is negative, D3 and D4 are turned on (b).

In either case, current flows through R in the same direction, resulting in an output voltage, vO, shown in (c).

### Output Voltage of Full-Wave Rectifier with RC Filter

The ripple on the ‘dc’ output is

### Output Voltage of Full-Wave Rectifier with RC Filter

Diode conducts current for only a small portion of the period.

### PSpice Schematic of Diode Bridge Circuit

Steady state output voltage for a 60Hz sine wave input with peak value of 13.4V.

### Demodulation of Amplitude-Modulated Signal

Modulated input signal

Detector circuit

Demodulated output signal

### Equivalent Circuits for Input Cycles

Negative input cycle Positive input cycle

### Voltage Regulator

The characteristics of the Zener diode determines VL.

### Design Example 2.5

The reverse bias I-V is important for Zener diodes.

### Voltage Rectifier with nonzero Zener resistance

The Zener diode begins to conduct when VPS = VZ.

When VPS≥ VZ:VL = VZ

IL = VZ/RL,, but VZ≠ constant

I1 = (VPS – VZ)/Ri

IZ = I1 - IL

### Diode and Resistor In Series

Voltage shift between input and output voltages in transfer characteristics is because the diode only conducts when v1≥ Vg.

### Diode with Input Voltage Source

Output voltage is a constant when the diode is not conducting, when v1≥ Vs - Vg.

### 2 Diode Circuit

Voltage transfer characteristics

### Problem-Solving Technique: Multiple Diode Circuits

• Assume the state of the diode.

• If assumed on, VD = Vg

• If assumed off, ID = 0.

2. Analyze the ‘linear’ circuit with assumed diode states.

3. Evaluate the resulting state of each diode.

4. If any initial assumptions are proven incorrect, make new assumption and return to Step 2.

### Exercise problem

D1 is not on.

D2 is on.

This pins VO to -0.6V

Vg = 0.7V

Vg = 0.7V