SMPS

Power Supply Any device that supplies electric power to an electric load. The different types of power supplies include: Battery DC power supply AC power supply Linear regulated power supply Switched mode power supply Programmable power supply Uninterruptible power supply

Switched Mode Power Supply An electrical power supply that incorporates a switching regulator to convert electrical power efficiently. It transfers power from a source, to a load, while converting voltage and current characteristics. Voltage regulation is achieved by varying the ratio of on-to-off time.

Advantages of SMPS over Linear Power Supplies 1. Lower weight 2. Smaller size 3. Higher efficiency 4. Lower power dissipation 5. Wide ac input voltage range 6. Reduced costs Disadvantages of SMPS: 1. Complexity of the circuit

Block diagram of a SMPS Input rectifier stage: It is used to convert an AC input to DC.

2. Inverter stage: The inverter stage converts DC, whether directly from the input or from the rectifier stage 3. Output transformer: If the output required is to be isolated from input, the inverted AC is used to draw the primary windings of a high frequency transformer. This converts the voltage up or down to the required output level on it’s secondary winding. 4. Output rectifier: If the dc output is required, the ac output from the transformer is rectified. Regulation: Feedback circuit monitors the output voltage and compares it with the reference voltage.

Factors to be considered while selecting a topology for a particular application 1. Is input-to-output? 2. Are multiple outputs required? 3. Does the prospective topology place a reasonable voltage stress across the voltage semiconductors? 4. Does the prospective topology place a reasonable current stress across the voltage semiconductors? 5. How much of the input voltage is placed across the primary transformer winding or inductor? Typical maximum output power available from each topology: Converter Topology Maximum output power Flyback 200W Forward 300W Push-pull 500W Half bridge 1000W Full bridge >1000W

Use of non-isolated topologies Non isolated topologies are the simplest, with the three basic types using a single inductor for energy storage. Type Power(W) Relative Cost Energy Storage Voltage Relation Features Buck 0-1000 1.0 Single inductor 0 ≤ Out ≤ In V2=D.V1 Continuous current at output Boost 0-150 Out ≥ In V2=V1.[(1)/(1-D)] Continuous current at input Buck-boost Out ≤ 0 V2= -V1[(D)/(1-D)] No continuous current

Use of various transformer isolated topologies

Applications of SMPS 1. Machine tool industries 2. Security Systems (Closed circuit cameras) 3. Support supplies with PLC’s 4. Personal Computers 5. Mobile Phone chargers