6.0 Voltage Regulators

6.0 Voltage Regulators 6.1 Power Supply Block Diagram 6.2 Voltage Regulation 6.3 Series Regulators 6.4 Shunt Regulators 6.5 Switching Regulators 6.6 Integrated Circuit (IC) Voltage Regulators 6.7 Regulator Application

Introduction Voltage regulator function is to provide a constant dc output voltage. Input voltage may come from rectifier ac voltage or from a battery. Voltage regulator part of dc power supply and can divide into two categories, linear and switching regulator. There are two types of linear regulator, series and shunt regulator. The popular voltage regulator IC is three terminal +ve and –ve which can be fixed and adjustable. Switching regulators are also widely used.

6.1 Power Supply Block Diagram Transformer –to step up or step down ac voltage amplitude. Also isolate secondary from primary power earth line and noise. Rectifier –three types half-wave, full-wave and bridge. The function is to convert from ac voltage to dc voltage. The output is pulse dc voltage with ripple voltage. Filter –using low-pass filter either capacitor filter or RC filter. The function is straighten the pulse dc voltage by eliminate the ripple. Voltage regulator -is the ability to establish a constant voltage reference.

Power Supply Block Diagram Power supply function is to convert from ac to dc voltage. It’s must able to maintain the current and voltage level.

6.2 Voltage Regulation Line Regulation Line regulation is a measure of the effectiveness of a voltage regulator to maintain constant dc voltage output despite changes in the supply voltage. It is define as a ratio of a change in output voltage for a change in input voltage

6.2 Voltage Regulation Load Regulation Load regulation is a measure of the ability of regulator to maintain constant dc Vout despite changes in load current. Ideally the load regulation is 0 %, and the formula is:

6.3 Series Regulators Control element is a pass transistor in series with load between input and output. Output sample circuit sense a change in the Vout. Error detector compares sample voltage with reference voltage, so control element will compensate in order to get a constant Vout.

6.3 Series Regulators Regulating Action In op-amp series regulator circuit, the resistive voltage divider formed by R2 and R3 senses any change in Vout. When Vout tried to decrease, coz Vin decrease or IL change, Vfb is applied to op-amp, a small diff will develop at op-amp (Vref–Vfb) is amplified and op-amp output will inc. This applied to base Q1, and emitter Vout inc, until Vref equal Vfb Q1 is power transistor with heat sink coz to handle IL. The opposite happen when Vout tries to inc. Voltage gain, Av= 1 + R2/R3. Output voltage, Vout=(1 + (R2/R3)) x Vref. Vout is determine by zener voltage, Vref and feedback ratio R2/R3.

6.3 Series Regulators It independent of the input voltage, and therefore regulation is achieved as long as the input voltage and load current are within specified limits.

Exercise If Vz= 5.1V, R1= 2.2KΩ, R2= 12KΩ and R3= 20KΩ, what is the output voltage, Vout, voltage gain, Av and Q1 base voltage. If Vz= 5.1V and Vout = 10.2V, what is the ratio of R2/R3.

6.3 Series Regulators IL(max) = 0.7V/R4 Short Circuit or Overload Protection The constant current limiting circuit Q2 and R4 use to prevent overload that cause the transistor to damaged. IL(max) = 0.7V/R4

6.4 Shunt Regulators The control element is a transistor, Q1 parallel (shunt) with the load and a resistor R1 in series with the load. The operation same as series, except that regulation is achieved by controlling the current through Q1.

6.4 Shunt Regulators

Exercise If Vin(max) = 12.8V and R1= 27Ω, what is the power rating of R1. If R1 = 47Ω and PR1 = 15W, what it the Vin(max).