DC-DC Converters Overview

What Is DC?

The term DC stands for direct current, which is a “unidirectional flow of electric charge”. People use DC power sources such as solar cells, batteries, and thermocouples. DC is flexible and able to transfer through conductors, such as wire, as well as through insulators, semiconductors, and even through a vacuum. The current always flows in just a single direction, which is the thing that differentiates it from AC, or alternating current, which can change direction.

People often use direct current as a means to charge batteries and their electronic devices. They also use DC power for third rail power systems and railway propulsion. While DC means direct current, it also means constant polarity. Some types of DC will have variances in their voltage, while most will not. A good example of varying voltage would be fluctuating voice signals on a power line. One should never try to reverse the polarity in a DC device, unless it features a diode bridge that will allow for the switch. Most of the battery-powered devices that people use do not have this bridge, so trying to alter the polarity would actually destroy the device.

The automotive industry and aircraft often use these types of systems. Most of the time, vehicles will use 12-volt power, although a select few may have 42-volt or 6-volt systems. Most light aircraft use 12-volt or 28-volt. Phone systems will often use both AC and DC components in them. Anything that contains a battery is running on DC power, from portable radios to toys.

 

How Is DC Different from AC?

Inventor Thomas Edison was a champion of DC power. He and others saw that electrical energy and magnetic fields had a close relationship. When there is a magnetic field near wires, it causes the electrons in the wire to flow in a single direction, which we’ve already established as being direct current. They flow because they are either attracted or repelled by the magnetic poles. This discovery showed scientists that it was possible to hold energy in a battery and then harness it.

However, DC was not the only source for electricity. Another scientist, Nikola Tesla, worked on the alternating current system because it was able to transfer power more efficiently, he thought. He did not make use of magnetism on the wire in a steady direction. Instead, the magnet rotated, offering alternating power. When the magnet was in a certain position, the electrons would flow in one direction. Changing, or alternating, the position of the magnet would change the way the electrons flowed.

One of the biggest differences in AC and DC is the amount of energy they can carry. DC voltage can produce a certain amount of constant electricity. The further it travels the weaker it becomes. AC voltage from generators can change their strength, increasing or decreasing it when they travel through transformers.

By using an adapter, it is possible to change AC energy to DC energy. This happens in many electronic devices, such as musical keyboards, laptop computers, and other devices that require adapters.

 

What Is DC-to-DC Conversion?

A DC-DC converter is a type of electronic circuit that takes the DC source and then converts it from the current voltage into another voltage. In some instances, one may have to increase or decrease the voltage. This is actually very common when it comes to automobiles. Some devices you might use in your vehicle, such as a portable DVD player for the kids, require a certain amount of power to run. Too much power and it could destroy the devices. Too little power and it would not run. Since the device needs to draw from the vehicle’s battery, and the battery might be too powerful, there needs to be a conversion of power. However, it needs to remain DC voltage. To accomplish this, a variety of different types of DC-DC converters is available.

The converters will actually take the power from the battery and cut it down to a usable level. In the cases of devices that might need more power, a converter can step up the power. Many of the devices that you use in the vehicle come with adapters that you can plug into the vehicle. The adapters will convert the power to ensure your device works appropriately. It is important to make sure you are always using the right adapter with the device though. Otherwise, it could be drawing too much power, which could seriously damage the electronics.

 

Why Is It Necessary to Convert DC to DC?

Unlike AC power, it is not possible to increase or decrease the voltage level with a transformer. In some cases, it might be necessary to step down from the power coming from a large truck battery running on 24 volts to 12 volts in order to power a radio. In cars, the 12-volt battery provides too much power to some connected devices, such as a phone. So, they need to have a converter that will drop the power even further and make it safe for the device.

 

What Are DC-DC Converters?

Because there are a number of different needs for DC-DC converters, a variety of types are available that can help with different jobs. Some of the converters will be suitable for certain tasks, while others will not, so it is important for the user to know the exact specifications of the converters they are using so they do not damage any of their equipment. Some of the converters will step up the power, while others will step it down. Some converters actually have the capability to do either.

 

How Does a DC Converter Work?

The basic DC-DC converter will take the current and pass it through a “switching element”. This turns the signal into a square wave, which is actually AC. The wave then passes through another filter, which turns it back into a DC signal of the appropriate voltage necessary.

 

What Is the Difference Between Isolated and Non-Isolated DC-DC Converters?

Two of the terms commonly found around DC-DC converters are non-isolated and isolated converters. The non-isolated converters are often used when the change in voltage is small. Five different types of converters fall into this group. The input and output terminals share a “common ground”. The DC-DC converters are very common, and they are generally a cheaper solution for most devices. One of the disadvantages with the non-isolated converters is that they do not have much in the way of protection for high electrical voltages. They often have more noise as well.

 

  • Buck – The buck converter is used whenever one needs to reduce the amount of voltage.
  • Boost – A boost converter does the opposite of the buck converter. It steps up the voltage level.
  • Buck-Boost – This type of converter can work as either bucking or boosting the voltage. The most common usage for the converter is to reverse polarity.
  • Cuk – This type of converter is similar to buck-boost converters. The biggest difference is really the name. The Cuk was named after Slobodan Cuk, the man who created it.
  • Charge-Pump – This converter is used for stepping the voltage up or down in applications that have low power.

 

With an isolated DC-DC converter, there is a separation between the input and output terminals. These converters have high isolation voltage properties. They are useful for negative or positive grounds, and they can also be used as a floating ground for different types of equipment, such as telecommunications equipment. Unlike non-isolating converters, they have the ability to block noise and interference. This allows them to provide a cleaner DC source. In addition, they are generally safer. Two basic types of isolated converters exist.

 

  • Flyback Converter – The converter works similarly to the buck-boost converter in the non-isolating category. The difference is that it makes use of a transformer to store the energy instead of an inductor.
  • Forward Converter – Forward converters are very different. The converter will use the transformer to send the energy between input and output in a single step.

 

There are three classes of isolation:

 

  • Operational – This offers isolated output with fault protection.
  • Basic – The basic form of isolation will offer a transformer with single fault protection.
  • Reinforced – This features two isolation layers that can offer actual physical separation.

 

Both the isolating and non-isolating converters have their uses, and the right choice will always depend on the application and individual needs. Even the best converters will have some loss in energy. Choosing the right converters can help to limit loss, and it ensures you are using the best option for each application no matter the size.

 

What Types of DC-DC Converters Exist?

  • Fixed Installation Car Power Adapters – The power that comes into your vehicle from the battery may be too high for powering some of the modules and devices, so the manufacturers will often utilize power adapters to ensure you are receiving the right voltage for the devices. They are available at various input and output voltages to ensure the best and safest performance. They also have surge protection and short circuit protection.
  • Isolated DC-DC Converters – As mentioned, these have internal transformers that will transform the input to a different output voltage for use with your equipment. With this converter, the output is isolated from the input.
  • Non-Isolated DC-DC Converters – As the name suggests, they do not have any isolation between the input and output. They are typically used for smaller voltages. They can step the voltage up or down, and some of the converters have the ability to do either.
  • Portable Car Power Adapters – Portable car power adapters are very handy devices that people can use with all sorts of electronics to make them usable with their vehicle. They can serve as an adapter for a DVD player, CD player, phone connector, and more. The purpose of these adapters is to take the DC power that comes in from the vehicle’s battery and step it down so that it can work with personal electronic devices without providing them with a voltage that is too high and that might damage them. It is important to purchase the correct adapters to ensure they actually provide the correct protection for the electrical devices.

 

What Are Switching Regulators? How Do They Work?

A switching regulator will create a certain fixed output voltage that can remain constant regardless of any changes that happen to the input voltage. Two different types of regulators are available – switching and linear.

The linear regulator uses a high gain differential amplifier to control the active pass device. The regulator will compare the voltage being output with the reference voltage and make adjustments as a means to ensure the output voltage is always constant. Most of the time, linear regulators will power devices that have low power.

They are quite common, easy to use, and they are relatively cheap. They do have some disadvantages though. They are not as efficient as switching regulators, as they can lose a substantial amount of energy. The regulators will generally have efficiencies on the high end at about 40%. Some are even lower.

The switching regulators on the other hand will convert the DC input voltage to a switched voltage that feeds back to the circuit that controls the on and off power switch. It can turn the switch on or off as a means to keep the output voltage constant no matter what the load current or input voltage might be. The switching regulators use smaller bits of energy than the linear regulators, which help to give them a higher level of efficiency.

The DC-DC converters help to make it easy to get just the right amount of DC voltage for a variety of different devices. Choosing the right type of converter or adapter for the job is vital to ensure the safety of anyone using the device as well as for the safety of the device itself.