Hello Folks,
To understand any complex DC-DC Converter in Power Electronics, knowledge of basic converters is obligatory. AC-AC conversion can be easily done with a transformer; however dc-dc conversion is not as simple. Diodes, voltage bridges and voltage regulators are found to be inefficient for this. The most efficient method of regulating voltage through a circuit is with a dc-dc converter.
The dc-dc converters can be viewed as dc transformers that deliver to the load a dc voltage or current at a different level than the input source. This dc transformation is performed by electronic switching means, not by electromagnetic means such as in conventional transformers. The output voltages of dc-dc converters range from one volt for special VLSI circuits to tens of kilovolts in X-ray lamps.
DC-DC power converters are employed in a variety of applications, including power supplies for personal computers, office equipment, spacecraft power systems, laptop computers, and telecommunications equipment, as well as dc motor drives.
The three basic types of DC-DC converter circuits are buck, boost and Buck-Boost. The Buck converter may consequently be seen as a Voltage to Current converter, the Boost as a Current to Voltage converter and the Buck-Boost as a Voltage-Current-Voltage Converter.
The very 1st Basic building block of advanced DC-DC Converter is Cuk Converter. Cúk converter is used as a Current-Voltage-Current converter. Cúk converter is actually the cascade combination of a boost and a buck converter. It provides an output voltage that is less than or greater than the input voltage & the output voltage polarity is opposite to that of input voltage.
Many years ago, Dr. Cúk invented the integrated magnetic concept called DC-transformer, where the sum of DC fluxes created by currents in the winding of the input inductor L1 and transformer T is equal to DC flux created by the current in the output inductor L2 winding. Hence the DC fluxes are opposing each other and thus result in a mutual cancellation of the Dc fluxes.
It combines the characteristic low input current ripple of the boost converter with the low output current ripple of the buck converter. The buck, boost and Buck-Boost converters all transfer energy between input and output using inductor and analysis is based of voltage balance across the inductor. The CÚK converter uses capacitive energy transfer and analysis is based on current balance of the capacitor.
The ideal switch (and ideal components) circuit diagram for the Cuk converter with BJT NPN transistor (Self-commuted device) used as a switch is shown in Fig 1
Fig 1: Cúk Converter with BJT used as a switch
To understand any complex DC-DC Converter in Power Electronics, knowledge of basic converters is obligatory. AC-AC conversion can be easily done with a transformer; however dc-dc conversion is not as simple. Diodes, voltage bridges and voltage regulators are found to be inefficient for this. The most efficient method of regulating voltage through a circuit is with a dc-dc converter.
The dc-dc converters can be viewed as dc transformers that deliver to the load a dc voltage or current at a different level than the input source. This dc transformation is performed by electronic switching means, not by electromagnetic means such as in conventional transformers. The output voltages of dc-dc converters range from one volt for special VLSI circuits to tens of kilovolts in X-ray lamps.
DC-DC power converters are employed in a variety of applications, including power supplies for personal computers, office equipment, spacecraft power systems, laptop computers, and telecommunications equipment, as well as dc motor drives.
The three basic types of DC-DC converter circuits are buck, boost and Buck-Boost. The Buck converter may consequently be seen as a Voltage to Current converter, the Boost as a Current to Voltage converter and the Buck-Boost as a Voltage-Current-Voltage Converter.
The very 1st Basic building block of advanced DC-DC Converter is Cuk Converter. Cúk converter is used as a Current-Voltage-Current converter. Cúk converter is actually the cascade combination of a boost and a buck converter. It provides an output voltage that is less than or greater than the input voltage & the output voltage polarity is opposite to that of input voltage.
Many years ago, Dr. Cúk invented the integrated magnetic concept called DC-transformer, where the sum of DC fluxes created by currents in the winding of the input inductor L1 and transformer T is equal to DC flux created by the current in the output inductor L2 winding. Hence the DC fluxes are opposing each other and thus result in a mutual cancellation of the Dc fluxes.
It combines the characteristic low input current ripple of the boost converter with the low output current ripple of the buck converter. The buck, boost and Buck-Boost converters all transfer energy between input and output using inductor and analysis is based of voltage balance across the inductor. The CÚK converter uses capacitive energy transfer and analysis is based on current balance of the capacitor.
The ideal switch (and ideal components) circuit diagram for the Cuk converter with BJT NPN transistor (Self-commuted device) used as a switch is shown in Fig 1
Fig 2a: Cúk converter with switch closed
Fig 2b: Cúk converter with switch open
The input circuit in the Cuk converter is, clearly, a Boost converter and the output circuit is seen to be a Buck converter. The Cuk converter requires two (dependent) switches, two inductors L1 and L2, and two capacitors.
In fig 1, the capacitor C1 acts as a primary means to store and transfer the power from input to output. As a result, the input current is continuous (unlike buck-boost converter). The voltage vc1 is always greater than either input or output voltage. Due to the inductor on the output stage, the Cúk converter can provide a better output current characteristic. The average output to input relations are similar to that of a Buck-Boost converter circuit. The output voltage is controlled by controlling the switch-duty cycle. It can be used for step up and step down of voltage by varying duty ratio in the equation,
Vo/Vin = D/ (1-D)
Operation of converter into two modes:
Mode-1:- When BJT switch is turned on, the current through L1 rises and at the same time the voltage of C1 reverse biases diode D hence turning it off. The capacitor C1 discharges its energy to the circuit C1-C-load-L2. (Fig. 2a)
Mode-2:- When BJT switch is turned off, the capacitor will start to charge from input supply Vin and the energy stored in the inductor is transferred to the load. The capacitor C1 is the medium for transferring energy from source to load. (Fig. 2b)
The circuits have low switching losses and high efficiency. Cúk converter provides capacitive isolation which protects against switch failure (unlike the buck topology). With Cúk converter energy is transferred when switch opens and also when switch is closed (This doesn’t exists in case of buck and boost converter). It uses L-C filter, so peak-peak ripple current of inductors are less compared to Buck-Boost converter.
We will shortly discuss the other Advanced DC-DC Converters. Thank you for your time.
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