The definition of SMPS is that when a switching regulator contains a power supply, the conversion of electrical energy from one form to another with the necessary characteristics is called a switching mode power supply. This power supply is used to obtain a stable DC o / p voltage from a DC i / p voltage or unregulated AC.
The working of SMPS can be understood by the following figure.
The 50 Hz AC input power signal is directly provided to the rectifier and filter circuit combination without using any transformer. There will be many changes in the output, and the capacitance of the capacitor should be higher to cope with input fluctuations. This unregulated DC power is supplied to the central switching part of the SMPS.
In this section, a fast switching device, such as a power transistor or MOSFET, is used. The switching device switches ON and OFF according to changes and provides this output to the primary stage of the transformer present in this section. Unlike transformers used for 60 Hz power supplies, the transformers used here are smaller and lighter. These are very effective, so the power conversion ratio is higher.
The output signal from the switch section is rectified and filtered again to obtain the required DC voltage. This is the adjusted output voltage, which is then provided to the control circuit as a feedback circuit. The final output is obtained after considering the feedback signal.
This unit is the feedback circuit which has many sections. Let us have a clear understanding about this from The following figure.
The figure above illustrates the internal components of the control unit. The sensor sensing signal is output and added to the control unit. This signal is isolated from another part, so any sudden spikes will not affect the circuit. The reference voltage is provided as an input to the error amplifier together with the signal. The error amplifier is a comparator that compares the signal with the desired signal level.
By controlling the chopping frequency, the final voltage level can be maintained. This is controlled by comparing the input of the error amplifier, which helps determine whether to increase or decrease the chopping frequency. The PWM oscillator generates a standard PWM waveform with a fixed frequency.
We can get a better idea on the complete functioning of SMPS by having a look at the following figure.
The SMPS is mostly used where switching of voltages is not at all a problem and where efficiency of the system really matters. There are few points which are to be noted regarding SMPS. They are
- The SMPS circuit operates by switching, so the voltage changes continuously.
- The switchgear operates in saturation or cut-off mode.
- The output voltage is controlled by the switching time of the feedback circuit.
- Adjust the switching time by adjusting the duty cycle.
- SMPS is very efficient because it continuously switches its input to control the output, rather than dissipating excess power into heat.
- The switch mode power supply (SMPS) is used in personal computers.
- It is used in machine tool industries.
- The SMPS is used in security system.
- It is used in railway system.
- It is also used in mobile.
- It is used in battery charger.
- The SMPS is used in vehicles.
- It is also used in lighting.