Block diagram and working of SMPS (Switched Mode Power Supply)

Figure: Block diagram of SMPS

    Figure shows block diagram of SMPS i.e. switched mode power supply which is electronic power supply used generally to provide DC constant output. SMPS (switched mode power supply) is the power supply which consists of switching regulator (to control output) to convert electrical power efficiently and deliver it by DC source or AC source to DC loads (like a PC (personal computer)).  The pass transistor of a SMPS switches continuously between states like low-dissipation, full-ON, full-OFF, and spends very little time in the high dissipation transitions. This is done to achieve minimum energy wastage. Voltage regulation is done by changing the ratio of on-to-off time. 

Working of SMPS :-

Rectifier and filter:

Rectifiers are used to convert the AC supply voltage to a pulsating dc, which is then filtered out to reduce the ripple content. Power diodes are used in a bridge configuration to form rectifier circuit in order to obtain the pulsating dc and capacitor (and/or inductor) is used as a filter element to remove ripple factor.

High-frequency switching:

It uses either MOSFETs or BJTs to convert the dc voltage to high frequency ac square wave which typically ranges from 20 kHz to 100 kHz. Here, transistors are not used in active region hence it results in low power dissipation. Thus, it is a two stage conversion. i.e. the input ac supply voltage is first rectified to dc and then the high- frequency switching section changes it back to ac.

High frequency power transformer:

It isolates the circuit and steps-up or steps-down the voltage to the desired voltage level. The output of the transformer is the input of the second rectifier section, called the output rectifier section.

Output rectifier: 

Rectifier section is different from the first block of the rectifier in that the frequency of the voltage is very high. Therefore, the bridge configuration of this rectifier uses a high frequency diode (like Schottky diode) and the ripple factor present in output is filtered because of the number of overlaps between each individual output pulse. Since the ripple is very small in the output voltage of the rectifier, a small capacitance value is required in the filter section.

Control and feedback:

It provides a pulse width modulation(PWM) output signal. The PWM controller are used to serve a duty-cycle that changes the pulse by pulse in order to produce  accurate DC output voltage.