How to work SMPS

What is SMPS

The SMPS stands for Switch Mode Power Supply, it is basically a electronics device which used for power supply, it convert high "AC" voltage into low "DC" voltage.

The SMPS mostly used where we needs low "DC" voltage or which equipment we operates by "AC" current but there equipment required "DC" current or voltage, then we use SMPS, such as Computer, Laptop charger, LED, and etc.

How to Works SMPS:-

As the its name shows that it works at Switching mode, means it work at high frequency, the SMPS used the buck converter concept, but its difference that it can works by "AC" current.

SMPS block diagram 

SMPS block diagram

Step 1

First we supplied "AC" normal voltage to Diode, then diode convert "AC" current to "DC", but when diode "AC" current convert to "DC" current so this current will not pure.

Step 2

Which current out from diode this current will provide to capacitor, because which current is out from diode it is not pure, for this we used capacitor, also capacitor used for voltage input voltage maintenance and keeping stable to voltage.

Step 3

When current reached at step 3 then voltage will pure and high, so in this step, we will attach a switching device such as transistor, we using transistor for switching, because a transistor can easily convert normal or zero frequency to high frequency, in SMPS we require very high frequency like 50-100 kilo hertz or above, because in next 4th step we will use a chopper transformer.

The transistor controlled by PWM circuit, the PWM stands for Pulse width modulation, it is basically a complete circuit which controls to transistor switching, because transistor’s switching is effected on output voltage.

Step 4

Now we get "AC" current but at high frequency, when the our input frequency is normal 50-60 hertz "AC" current, but here we needs high frequency "AC" current.

Because in SMPS we used chopper transformer and chopper transformer works only at high frequency.

In step 3 we Filtered "AC" current into "DC" current but again converted into "AC" current, so why first we AC current converted in DC current?

Because we want SMPS operates at both such as low or high voltage, and need high frequency current for chopper transformer, so only transistor can convert low frequency to high frequency, and transistor only operates by "DC" current, it cannot work by "AC" current, for this we used diode/rectifier that "AC" current convert to DC.

And also we required stable and pure voltage for transistor, so we used Capacitors in the circuit, also capacitor can increasing the voltage.

For this SMPS can smoothly work at low input voltage.

Step 5

Chopper transformer gets high voltage at high frequency, then it will step down the voltage at high frequency, means it give low voltage at high frequency.

We design the chopper transformer according to our choice, ie the transformer is made according to the voltage requirement.

Step 6

Now which voltage gets by chopper, this is AC current but we require DC current, so again we use Diode and Capacitor for current changing and filtering.

Now we are get DC step down voltage.

The SMPS voltage always remain same such as if it give 12v DC at with load then it give constant 12v without load, its voltage will not change by load.

Because we use feedback signal in its circuit, the output voltage with connect to output sensor, which sense the voltage and give signal to PWM circuit, then PWM circuit will control the transistor switching by output voltage, so when voltage will increase or decrease then output feedback signal transfer to PWM circuit and PWM circuit will increase or decrease to transistor's switching.

Why chopper transformer used in SMPS not normal transformer?

The chopper transformer is very small in the size than normal transformer, and it can supply high current by thin wire, which wire used for its windings.

And it can easily works at high frequency, basically its reduce the size by this property, that it can works at high frequency.

The SMPS basically operates by high frequency that its size can be reduce, if used normal transformer then required thick wire, means its wire size depends on its output current, so power supply's size will not be reduce, because we require big transformer for windings thick wire.

For this we used high frequency in SMPS because the high frequency is effected on current, we can use thin wire at high current by high frequency, so we needs SMPS works at high frequency, and the only chopper transformer can works at high frequency, for this we used chopper transformer not used normal transformer in SMPS circuit.

If we used normal core transformer, so it will not work at high frequency.

You see in every SMPS circuit that its chopper transformer has thin wire, but power supply out high current.

Difference between SMPS and Normal transformer power supply

1- The "SMPS" is the small in the size, and it has less weight, and normal "power Supply" is big in size and has high weight.

2- The "SMPS" always give constant and fixed voltage, and its voltage will not change by input voltage variation, when the normal "Power Supply" can't give fixed or constant voltage, its voltage will increase or decrease by input voltage variation.

3- The "SMPS" can easily works at low Input voltage, and it can support high voltage from normal voltage range, when the normal "Power Supply" can't work at low voltage, and its transformer can't support high voltage from normal voltage, if input voltge will increased so its windings can't support then its windings can burnt, it only operates at the voltage for which voltage it is designed.

4- The "SMPS" output voltage we can change from its circuit, but in normal "Power Supply's" voltage we can't changing, because it not has any circuit for output voltage changing, its voltage set in its winding when its winding designed.