Basics switching regulators

Definition, Operation , Working , Buck converter , Step up Configuration ,Step up Regulator Boost converter, Inverter configuration , Buck boost configuration ,Switch mode summary ,Advantages ,Disadvantages and Appplications

1. Basics Switching Regulators Definition :- A voltage regulator that using a switching element to transform a supply into an alternating current which is then converted to a different voltage using capacitors ,inductors and other elements ,then converted back to the DC .The circuit includes regulation and filtering components to insure a steady current.

2. Configuration Of Switching Regulators 1:- Step Down Regulator (Buck Converter) 2:- Step Up Regulator(boost Converter) 3:- Inverting Regulator (Buck Boost Converter)

3. OPERATION:-

4. It uses a transistor as a switch that alternately connects and disconnects the input voltage to a inductor. When the switch is turns ON the input voltage is connected to the inductor .The difference between input and output voltage is then forced across the inductor causing current through the inductor to increase. During the ON time the inductor current flows into both load and the output capacitor (the capacitor charges during this time). When the switch is turns OFF the input voltage applied to the inductor is removed . Since the current in the inductor cannot change instantly the voltage across the inductor will adjust to hold the current constant. WORKING

5. The input end of the inductor is forced negative in voltage by the decreasing current , eventually reaching the point where the diode is turned ON . The inductor current then flows through the load and back through the diode. The capacitor discharges into the load during the OFF time, contributing to the total current being supplied to the load (the total load current during the switch OFF time is the sum of inductor and capacitor current. ) The current through the inductor ramps up when switch is ON and ramps down when switch is OFF . The DC load current from the regulated output is the average value of the inductor current.

6. When output voltage V out is tries to decrease the ON time of Q1 is increased , causing an additional charge on C to offset the attempted decrease . The output voltage is expressed as:- V out =(t on/T)V in The off time is given by:- T=t on + t off When V out tries to increase the ON time of Q1 is decreased , causing the capacitor to discharge enough to offset the attempted increase.

7. It is also called a “BOOST CONVERTER” It takes a DC input voltage and produces a DC out put voltage that is higher in value then the input (but of the same polarity). Step Up Configuration

8. Step up Regulator

9. Out Put Current And Load Power The important deign of boost converter is that the output load current and the switch current are not equal , and the maximum available load current is always less then the current rating of the switch transistor. It should be noted that the maximum to total power available for conversion in any regulator is equal to the input voltage multiplied times the maximum average input current .(which is less then the current rating of the switch transistor. Since the output voltage of the BOOST is higher than the input voltage . It follows that the output current must be lower than the input current.

10. The Inverter Configuration It is also called “BUCK BOOST ” converter. It is step up type regulator. It takes a DC input voltage and produce a DC output voltage that is opposite in polarity to the input. The negative output voltage can be either larger or smaller in magnitude than the input voltage.

11. Buck Boost Working When the switch is ON the input voltage is forced across the inductor causing an increasing current flow through it . During the ON time the discharge of the output capacitor is only the source of load current. This requires that the charge is lost from the output capacitor during the on time be replenished during the OFF time. When the switch is turned Off the decreasing current in the inductor causes the voltage at the diode to swing negative . This action turns ON the diode allowing the current in the inductor to supply both the output capacitor and the load. The load current is supplied by the inductor when the switch is OFF and by the output capacitor when the switch is ON