DC converters convert direct current (DC) into regulated DC voltages using high-frequency switching and inductors. They operate with closed feedback loops to maintain a constant output voltage over input and load current changes.
They are available in isolated and non-isolated topologies and buck, boost, SEPIC, and buck-boost converters. They also have important datasheet parameters that are worth understanding.
1. Basic Concepts
DC converters, companies like Delta Electronic offer, are used in many electronic devices, including cellular phones and laptop computers. They help distribute power properly among various power-consuming sub-circuits, protecting them from damaging voltage levels and helping to keep overall device size down by using less space for power supply components. They are also used in portable devices to raise the voltage level of partially lowered batteries, allowing them to last longer.
A buck, boost, or cuk converter circuit uses a switching element that charges a storage capacitor with electrical pulses and then switches it off, transferring the stored energy to the output. A switch’s ON/OFF conversion generates a small amount of leakage current, reducing efficiency.
The more times the switch is flipped ON and OFF, the higher the loss will be. In addition, a MOSFET or bipolar switch has a small inherent impedance, which means some power travels through the switch and is wasted. This is why some switching regulators use snubbers in their designs to limit the impact of this wasted power.
Isolated and non-isolated DC-to-DC converter topologies are available for different applications based on the needs of each circuit or device. Non-isolated converters can be more cost-effective than isolated ones, as they don’t need to contain a transformer or other expensive components that can add to the device’s size and price. However, the high frequencies these converters use can cause problems with electromagnetic compatibility and other issues that need to be considered.
2. Switching Regulator
Unlike linear regulators, switching regulators use solid-state devices that are either completely on or off to perform power conversion. This makes them much more efficient and provides a clean output voltage. The DC output of the device is connected to a capacitor (CIN) and an operational amplifier (op-amp).
The op amp’s non-inverting input connects to an internal voltage reference, while its inverting input connects to an error signal generated by a feedback network consisting of R2 and R1. The error signal is based on the law of inductance, and the op-amp uses this information to modulate the PWM duty cycle to pull the output back into regulation.
The basic switcher has many variations, including buck, boost, flyback, half-bridge, and full-bridge designs. Some of these have isolated transformers, while others do not. The most common isolated versions are buck-boost and flyback, but other types also exist. These types offer different efficiency and output power levels; some provide multiple outputs with varying polarities.
They also support various configurations of feedback and error detection/recovery. When using a switching regulator, it’s essential to have adequate trace inductance and low parasitic resistance of the components. The high current pulses in the switching device can cause severe problems if the parasitics are too large.
3. Boost Regulator
The boost converter is a switch mode DC-DC power regulator that can “step up” an input voltage to some higher level required by a load. It stores energy in an inductor and quickly discharges it to the load via a switched-on transistor.
The efficiency of the boost converter is proportional to the ratio between the time of the switching transistor and the total switching period. This is why it is important to consider the rated voltages of the MOSFET and diode when choosing a candidate converter for a particular application.Boost and buck-boost converters offer unique solutions for applications where an input voltage is either higher or lower than the desired output. For example, lead-acid batteries can supply a high output voltage for LED lighting when charged, but when they’re depleted, their voltage will drop below the requirement of the circuit it is powering. In these cases, a buck-boost power regulator can increase the voltage and boost it to a stable supply.
4. Buck Regulator
Buck converters (also called step-down DC to DC converters) take an input voltage at Vin and produce a regulated output at Vout that is lower in magnitude. They are widely used because of their simplicity, efficiency, and compact size.
The basic buck circuit comprises an input voltage source, a switching device, an inductor, and a capacitor. The switching device – usually a power semiconductor switch like a MOSFET or IGBT – is turned on and off rapidly to chop the input voltage, creating a pulsing waveform. This is fed into the inductor, which stores energy in its magnetic field and transfers this to the load when the switch turns off. The capacitor smooths out the voltage ripple at the converter output for steady, regulated DC.
For high-efficiency operation, the inductor and capacitor should be carefully sized. The inductor must be rated for the peak current handled by the switching device. In contrast, the capacitor should be rated for the maximum load current and include a margin above this value to ensure stability under worst-case conditions.
Conclusion
DC converters play a pivotal role in managing and optimizing the power requirements of various electronic devices. Ranging from simple gadgets like cell phones to more intricate applications, these converters ensure that devices get the right voltage, enhancing their efficiency and longevity.
The article delved deep into various types of DC converters, including buck, boost, and SEPIC, showcasing their specific functionalities and efficiencies. Companies such as Delta Electronic have been at the forefront, offering these converters to facilitate a seamless power distribution amongst electronic sub-circuits.
