DC-to-DC Converters: Design, Working & Applications

What is a DC-to-DC Converters?

The DC-to-DC converters convert one level of DC voltage to another level. The operating voltage of different electronic devices such as ICs, MOSFET can vary over a wide range, making it necessary to provide a voltage for each device. A Buck Converter outputs a lower voltage than the original voltage, while a Boost Converter supplies a higher voltage.

With the application of DC-to-DC Converters, the circuit’s efficiency, ripple, and load-transient response can be changed. Optimal external parts and components are generally dependent on operating conditions such as input and output specifications. So, while designing the products, the standard circuits must be varied or changed according to and as per the need to their individual specification requirements. Designing the circuit that satisfies the specification and all the requirements needs a great deal of expertise and experience in that field.

The step-up or step-down DC-to-DC Converters are useful in applications where the battery voltage can be above or below the regulator output voltage. The DC to DC converter must be able to operate as a step up or down voltage supplier to provide constant load voltage over the entire battery voltage range through the operation.

Working Principle of DC-DC converter

The working principle of the DC-to-DC converter is very simple. The inductor in the input resistance has an unexpected variation in the input current. If the switch is kept as high (on), then the inductor feeds the energy from the input and stores the energy in the form of magnetic energy.

If the switch is kept as low (off), it discharges the energy. Here, the output of the capacitor is assumed as high that is sufficient for the time constant of an RC circuit on the output side. The huge time constant is compared with the switching period and made sure that the steady-state is a constant output voltage. It should be Vo(t) = Vo(constant) and present at the load terminal.

Types of DC-to-DC Converters

1: Magnetic Converters

In these DC-to-DC Converters, energy is periodically stored and released from a magnetic field in an inductor or a transformer. The frequency ranges from 300 kHz to 10MHz. By maintaining the duty cycle of the charging voltage the amount of power that needs to be transferred continuously to a load can be more easily controlled.

Moreover, the control can also be applied to the input current, the output current or to maintain constant power through the circuit. The transformer-based converter can easily provide the isolation between input and output.

2: Non-Isolated Converters

Non-isolated converters are mostly used when the change in the voltage is comparatively small. It posses the input and output terminal to a common ground. The major disadvantage is that it cannot provide protection from high electrical voltages and it poses more noise.

3: Step-down/Buck Converters

In a typical non-isolated step-down or buck converter the output voltage VOUT depends on the input voltage VIN and the switching duty cycle D of the power switch.

4: Step-up/Boost Converters

It is used to boost DC to DC converter voltage and it uses the same number of passive components but arranged to step up the input voltage so that the output is higher than that of the input.

5: Buck-Boost Converters

This converter allows the input DC voltage to be either stepped-up or stepped-down, depending on the duty cycle.

The output voltage is given by the relation as mentioned below:

1	VOUT = -VIN *D/ (1-D)

From the above expression, we can notice that the output voltage is always reversed in polarity with respect to the input. Therefore, a buck-boost converter is also known as a voltage inverter.

6: Isolated Converters

The Isolated converter has a separation between its input and output terminals. They have high isolation voltage properties. They can block the noise and interference. With this, they are able to produce a cleaner and desired DC output voltage. They are further categorized into two types.

I: Flyback converters

The working of this converter is similar to the buck-boost converter of the non-isolating category. The only difference is that it uses a transformer to store energy instead of an inductor in the circuit.

II: Forward Converters

The working of this converter makes use of the transformer to send the energy, between the input and output in a single step.

Advantages & Disadvantages of DC-to-DC Converters

Advantages

• It simplifies the power supply systems in the circuit.
• It provides isolation in the primary and secondary circuits from each other.
• It provides a technique to extend potential (voltage) as required.
• It is available as a hybrid circuit with all elements in a single chip.
• It is also used in the regulation and control of DC voltage.
• The output is well organized as positive or negative.
• Battery space can be reduced by using a converter.

Disadvantages

• Switching converters lead to more noise.
• They are expensive as an external circuit is required.
• Choppers are inadequate due to unsteady voltage and current supply.
• More ripple current, More input and output capacitance, higher losses, etc.

Check out some practical example circuits related to Buck & Boost DC-to-DC Converters.