Power electronics digital notes b. Tech III year

Figure: 3.22 circuit diagram of Buck regulator during switch off condition
Figure: 3.23 Input and output waveforms of Buck regulator

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In the diagram of the current waveforms for the buck converter / switching regulator, it can be seen that 
the inductor current is the sum of the diode and input / switch current. Current either flows through the 
switch or the diode. 
It is also worth noting that the average input current is less than the average output current. This is to be 
expected because the buck converter circuit is very efficient and the input voltage is greater than the 
output voltage. Assuming a perfect circuit, then power in would equal power out, i.e. Vin 
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In = Vout 
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Iout. While in a real circuit there will be some losses, efficiency levels greater than 85% are to be 
expected for a well-designed circuit. 
It will also be seen that there is a smoothing capacitor placed on the output. This serves to ensure that the 
voltage does not vary appreciable, especially during and switch transition times. It will also be required to 
smooth any switching spikes that occur. 
Boost regulator 
One of the advantages of switch mode power supply technology is that it can be used to create a step up 
or boost converter / regulator. 
Boost converters or regulators are used in many instances from providing small supplies where higher 
voltages may be needed to much higher power requirements. 
Often there are requirements for voltages higher than those provided by the available power supply - 
voltages for RF power amplifiers within mobile phones is just one example. 
Step-up boost converter basics 
The boost converter circuit has many similarities to the buck converter. However the circuit topology for 
the boost converter is slightly different. The fundamental circuit for a boost converter or step up converter 
consists of an inductor, diode, capacitor, switch and error amplifier with switch control circuitry.