Download 6.0 Voltage Regulators

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
a.
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.
b.
If Vz= 5.1V and Vout = 10.2V, what is the ratio of R2/R3.
6.3 Series Regulators
• 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
a.
If Vin(max) = 12.8V and R1= 27Ω, what is the power
rating of R1.
b.
If R1 = 47Ω and PR1 = 15W, what it the Vin(max).