smps

SMPSSMPSWhat 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

NecessityNecessity

The SMPS regulators are used in B.S.N.L at The SMPS regulators are used in B.S.N.L at various locations like CDOT, E10B and various locations like CDOT, E10B and Transmission systems etc. Transmission systems etc.

SMPSSMPS

Principle of Switching RegulatorPrinciple of Switching Regulator

A pulse train drives the base of ‘switching or A pulse train drives the base of ‘switching or pass transistor’. When the voltage to the 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 current When the transistor is OFF the load current is maintained by the energy stored in the is maintained by the energy stored in the choke L. The current flows through earth, choke L. The current flows through earth, Diode D, choke, load and earth. Hence this Diode D, choke, load and earth. Hence this diode is called ‘diode is called ‘Retrieval Diode’Retrieval Diode’..

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

SMPS

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

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

Principle of RegulationPrinciple of Regulation

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

RegulationRegulation If the output voltage tries to If the output voltage tries to

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


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

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 Block 4 Power factor corrector 100khzcorrector 100khz

Blokck 6-9 DC-DC converterBlokck 6-9 DC-DC converter

TELECOMMUNICATION ENGINEERING TELECOMMUNICATION ENGINEERING CENTRE (DOT) for the S.M.P.S. BASED CENTRE (DOT) for the S.M.P.S. BASED POWER PLANT GENERIC REQUIREMENTS POWER PLANT GENERIC REQUIREMENTS (No. G7SMP/-01/01 JULY 04)(No. G7SMP/-01/01 JULY 04)

Primary application of the rectifiers SMPS Primary application of the rectifiers SMPS 48V-5600W are in the supply of Telecom 48V-5600W are in the supply of Telecom equipment. The convection cooled unit may equipment. The convection cooled unit may be operated up to 60oC ambient air be operated up to 60oC ambient air temperature. temperature.

The rectifier operates from a nominal 3 X The rectifier operates from a nominal 3 X 230 Vac rms (with neutral wire) source. The 230 Vac rms (with neutral wire) source. The mains frequency may vary from 45 Hz to 65 mains frequency may vary from 45 Hz to 65 Hz. Total harmonic distortion (THD) of the Hz. Total harmonic distortion (THD) of the input current wave form is below 5%.input current wave form is below 5%.

smps

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