線性穩壓器 (1) Linear Regulators (1) Instructor: Po-Yu Kuo ( 郭柏佑 ) 國立雲林科技大學 電子工程系

This course mainly covers analysis and design of power conversion methodologies and controls including the following topics: Different types of DC-DC converters including linear regulator, charge pump (switched-capacitor power converters), and switched- mode power converter. Voltage reference that is used to define the output of the DC- DC converter. Frequency compensation techniques for multistage amplifiers that are useful to stabilize linear regulator. AC-DC converter (rectifier). This course mainly deals with the power conversion below 10W range. Course Contents 2

Power management circuits convert one type of a voltage or current waveform to another, and hence called converters. Converters are classified by the relationship between input and output: AC-DC (rectifier): average power is transferred from an ac source to a dc load. DC-DC: It converts an unregulated dc voltage or current to a regulated (specified) dc value with different dc value. DC-AC (inverter): average power flows from dc side to ac side. AC-AC: It is used to change the level and/or frequency of an ac signal. Power conversion can be a multistage process involving more than one type of converter. Converter Classification 3

All portable battery-powered electronic devices Applications of DC-DC Converters 4 Smart PhoneBluetooth Device Digital CameraIPod IPad

Continuous market growth of portable equipment drives the development of more new and advanced features in the portable equipment. All battery-powered portable devices such as cellular phones and PDAs need power management circuit (DC-DC Converters). Converter Classification 5 Battery Discharge Curves

In real circuits, more than one type of DC-DC converters are used in the power management system. Converter Classification 6

In real circuits, more than one type of DC-DC converters are used in the power management system. Types & Comparisons of DC-DC Converters 7 TypesBenefitsConcerns Linear regulator (low dropout regulator) 1. No magnetics 2. Simple and integrable 3. Low noise 1. Poor efficiency 2. No step-up operation Switched-capacitor power converter (charge pumps) 1. No magnetics 2. Step-up possible 3. Integrable 1. High switch count 2. Limited transfer ratio 3. High loss and noise Switched-mode power converter 1. High efficiency 2. Low switch count 1. Use inductor (larger electromagnetic interference) 2. High noise

Switched-Mode Power Converters (SMPCs) DC-DC conversions from Li-Ion cell battery (nominal 3.6V) to low supply voltage (1.2V) for internal digital baseband processors. Dynamically adjust supply voltages in RF power amplifier. Applications of Different PMICs in Cellular Phones 8

All power harvesting (batteryless) applications including RFID Tags, biological implanted devices, wireless sensors networks, etc. Example of power harvesting system Rectifier performs rectification to convert the sinusoidal voltage waveform from the receive coil to a dc voltage for further regulation. Efficiency of rectifier determines the efficiency of system power transfer. Applications of AC-DC Converter 9

Why we need voltage regulator? Voltage regulator is an electronic device to provide a well-specified and stable (regulated) voltage from a less stable (unregulated) voltage supply for powering other electronic devices. Linear regulator is used to describe an electronic regulator in which the voltage or current is controlled using transistors or other active devices as variable impedance elements. Basic Concept of Low-Dropout Regulator 10

This type of regulator is called the linear regulator because the transistor (BJT) operates in the linear region, rather than in the saturation or cutoff region. In MOS transistor, it operates in saturation (pinch-off) region, but the regulator is still known as a linear regulator. Basic Concept of Low-Dropout Regulator 11

Regulators can be divided into two groups: shunt regulators and series regulators: A shunt regulator has a variable impedance element in parallel with the load. The regulator diverts current from the load and thus control the load voltage. A series regulator has a variable impedance element connected in series between the unregulated power source and the load. The voltage across the load is sensed and impedance of the series element varied so as to keep the load voltage constant Basic Concept of Low-Dropout Regulator 12

Line (Load) regulation of a voltage regulator is determined by its ability to maintain a constant output voltage as input voltage (output current) varies: Line Regulation = Load Regulation = Efficiency of the regulator can be written as Efficiency( ) = Important Definition 13

The simplest way of shunt regulator uses the reverse breakdown of a Zener diode. The breakdown voltage due to Zener breakdown mechanism has a negative (- ve) temperature coefficient, while the breakdown voltage due to the avalanche multiplication has a positive (+ve) coefficient. At a breakdown voltage of 5V, both effects are active and the net temperature coefficient is close to zero. Therefore, Zener diode is a good candidate for a voltage regulator. Zener Diode Characteristics 14

When the zener diode is forward biased, it acts as a normal diode: When it is reversed biased, the current follows the diode equation until the diode undergoes zener breakdown (by tunneling) usually at a voltage of 6 - 7V. The exact IV characteristic of a zener diode in reverse breakdown region has a rather complicated mathematical expression. For simplicity, it is modeled as a battery (V zk ) in series with a resistor (r z ): Zener Diode Regulator 15

The circuit of a simple zener diode regulator is as: We need to express V o in terms of V in, V ZK and I L by (1) and (2): Zener Diode Regulator 16

As zener diode current I z > 0, the load current should be For good line and load regulations, both require a small rz which is <<Rs The efficiency of the regulator is given as Zener Diode Regulator 17

A shunt regulator : Find the line and load regulations of above circuit where V in =26V. Example 18