Smps

1. SMPSSMPS
What is SMPS?
SMPS means Switch Mode Power
Supply. This is used for D.C to D.C
conversion. This works on the principle of
switching regulation. The SMPS system is
highly reliable, efficient, noiseless and
compact because the switching is done at
very high rate in the order of several KHz
to MHz

2. NecessityNecessity
The SMPS regulators are used to provide The SMPS regulators are used to provide
regulated voltage for various equipments like regulated voltage for various equipments like
PC, CFL, TV, etc.PC, CFL, TV, etc.

3. SMPSSMPS
Principle of Switching RegulatorPrinciple of Switching Regulator

4. A pulse train drives the base of ‘switching A pulse train drives the base of ‘switching
or pass transistor’. When the voltage to the or pass transistor’. When the voltage to the
base is high, the transistor saturates, when base is high, the transistor saturates, when
the voltage is low, the transistor turns off. the voltage is low, the transistor turns off.
Here the transistor functions as a switch. Here the transistor functions as a switch.
When the transistor is ON, load current is When the transistor is ON, load current is
drawn through the transistor and choke L. drawn through the transistor and choke L.
When the transistor is OFF the load When the transistor is OFF the load
current is maintained by the energy stored current is maintained by the energy stored
in the choke L. The current flows through in the choke L. The current flows through
earth, Diode D, choke, load and earth. earth, Diode D, choke, load and earth.
Hence this diode is called ‘Hence this diode is called ‘Retrieval Diode’Retrieval Diode’..

5. Duty cycle of the Transistor D Duty cycle of the Transistor D = = On Time On Time
On Time + Off TimeOn Time + Off Time
(one cycle time)(one cycle time)
The output voltage = Input voltage x D

6. For exampleFor example
If I/P voltage is 200 volts and D=0.25If I/P voltage is 200 volts and D=0.25
O/P voltageO/P voltage = 200 x 0.25 = 200 x 0.25 = 50V.= 50V.
Regulation is achieved by modifying the Regulation is achieved by modifying the
Duty cycle. Duty cycle depends on Duty cycle. Duty cycle depends on
onetime of transistor, which in turn onetime of transistor, which in turn
depends on the width of the pulse applied depends on the width of the pulse applied
to the base of the transistor, which is to the base of the transistor, which is
controlled by ‘Pulse width modulation’ by controlled by ‘Pulse width modulation’ by
regulator circuitregulator circuit

7. Principle of RegulationPrinciple of Regulation

8. RegulationRegulation

The relaxation oscillator produces a square The relaxation oscillator produces a square
wave. The square wave is integrated to get a wave. The square wave is integrated to get a
triangular wave, which drives the non-inverting triangular wave, which drives the non-inverting
input of a triangular to pulse converter. The input of a triangular to pulse converter. The
pulse train out of this circuit then drives the Pass pulse train out of this circuit then drives the Pass
Transistor. The output is sampled by a voltage Transistor. The output is sampled by a voltage
divider and fed to a comparator. The feed back divider and fed to a comparator. The feed back
voltage is compared with a reference voltage. voltage is compared with a reference voltage.
The output of the comparator then drives the The output of the comparator then drives the
input of the triangular to pulse converter input of the triangular to pulse converter

9. RegulationRegulation
If the output voltage tries to increase If the output voltage tries to increase
the comparator produces a higher the comparator produces a higher
output voltage which raises the output voltage which raises the
reference voltage of the triangular- reference voltage of the triangular-
to pulse converter. This makes the to pulse converter. This makes the
pulse that drives the base of the pulse that drives the base of the
switching transistor narrower. That switching transistor narrower. That
means duty cycle is reduced. Since means duty cycle is reduced. Since
the duty cycle is lower the output the duty cycle is lower the output
becomes less which tries to cancel becomes less which tries to cancel
almost all the original increase in almost all the original increase in
output voltageoutput voltage. .

10. RegulationRegulation

Conversely, if the regulated output voltage Conversely, if the regulated output voltage
tries to decrease, the output of the tries to decrease, the output of the
comparator decreases the reference comparator decreases the reference
voltage of the triangular -to pulse voltage of the triangular -to pulse
converter. This makes the pulse wider and converter. This makes the pulse wider and
the transistor conducts for larger time and the transistor conducts for larger time and
more voltage comes out of the L.C.filter. more voltage comes out of the L.C.filter.
This cancels out the original decrease in This cancels out the original decrease in
output voltage output voltage

11. RegulationRegulation

14. Input SectionInput Section
Block 1 EMIBlock 1 EMI
Block 2 Current limiterBlock 2 Current limiter
Block 3 Floate Block 3 Floate
Block 4 Power factor corrector Block 4 Power factor corrector
100khz100khz
Blokck 6-9 DC-DC converterBlokck 6-9 DC-DC converter

15. 
TELECOMMUNICATION ENGINEERING CENTRE TELECOMMUNICATION ENGINEERING CENTRE
(DOT) for the S.M.P.S. BASED POWER PLANT (DOT) for the S.M.P.S. BASED POWER PLANT
GENERIC REQUIREMENTS (No. G7SMP/-01/01 GENERIC REQUIREMENTS (No. G7SMP/-01/01
JULY 04)JULY 04)

Primary application of the rectifiers SMPS 48V-Primary application of the rectifiers SMPS 48V-
5600W are in the supply of Telecom equipment. The 5600W are in the supply of Telecom equipment. The
convection cooled unit may be operated up to 60oC convection cooled unit may be operated up to 60oC
ambient air temperature. ambient air temperature.

The rectifier operates from a nominal 3 X 230 Vac The rectifier operates from a nominal 3 X 230 Vac
rms (with neutral wire) source. The mains frequency rms (with neutral wire) source. The mains frequency
may vary from 45 Hz to 65 Hz. Total harmonic may vary from 45 Hz to 65 Hz. Total harmonic
distortion (THD) of the input current wave form is distortion (THD) of the input current wave form is
below 5%.below 5%.