DC-to-DC Converter
A DC-DC converter (also called a DC-DC converter) converts an input DC voltage into a DC voltage with a higher or lower voltage, or inverts it.
The following is an overview of the most important DC-DC converters which we discuss here:
Overview DC-to-DC Converter
Linear or switching converters
Linear DC-to-DC-Converter
The linear DC-to-DC converter uses a resistive voltage drop to generate a specified output voltage. Apossible circuit would be this:
Function of a linear DC-DC-Converter
+ Linear DC-DC converters generate only minimal noise.
+ Cost-effective
- Power loss due to the pass transistor, which manifests itself in the form of heat. Heat sink required for the transistor.
- Efficiency depends on the voltage between input and output.
Switching DC-to-DC converters
A switching DC-to-DC converter periodically stores the input energy and then releases this energy in the form of a voltage of varying levels at the output.
Inductors or capacitors are used for temporary storage. If a transformer is used, this also provides galvanic isolation between the input and output.
Step-down converter (buck)
In a step-down converter (buck), the output voltage is lower than the input voltage and depends not only on the input voltage level but also on the duty cycle of the power switch.
Switching converter - Buck Converter (Step-Down)
When the switch is closed, current flows through the inductor, causing it to store energy in the form of a magnetic field. When the switch is opened, the coil releases its stored energy in such a way that it attempts to maintain the current. The current flows through the diode and charges the capacitor, allowing an output voltage to be taken.
In practice, a MOSFET controlled by a PWM signal is used for the switch.
Step-Up Converter (Boost)
With a boost converter, the output voltage is higher than the input voltage. For most practical applications, the maximum output voltage is approximately five times the input voltage.
Switching converter - Boost Converter (Step-Up)
When S1 is switched on, the coil L stores energy in its magnetic field. When S1 is switched off, this energy is added to the input voltage already applied to the capacitor and passed on to the output.
Isolated DC-to-DC Converters (with transformer)
In many applications, such as in medical technology, galvanic isolation is essential. This can be achieved, for example, by using a transformer without a common ground. Such converters are also known as isolated DC-DC converters.
Isolated DC-to-DC Converters (with transformer)
The transformer serves both as an energy storage device and for galvanic isolation. Since a transformer also incurs losses, only a few flyback transformers achieve an efficiency of more than 90 percent.
However, the use of a transformer, due to its turns ratio, allows for a wider range of output voltages. Furthermore, additional secondary windings can provide multiple output voltages.