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March 2, 2023
With 5G on the horizon, and its heavier power demands, traditional telecom rectifiers aren’t cutting it anymore. By only providing up to 48V DC to devices, along long lengths of cables, companies and the environment can no longer afford the energy and cost inefficiencies that come along with them. That’s where Class 4 telecom rectifiers come in.
Chapters:
What a Telecom Rectifier is & How It Works
Example Anatomy of a 3-Phase Telecom Rectifier
Where telecom rectifiers fit into telecom infrastructure
Typical Telecom Rectifier Specifications
Rectifiers, including traditional telecom rectifiers, are essentially AC to DC power converters. AC (alternating current) power needs to be converted into DC (direct current) power when powering DC devices (such as 5G antennas for both macrocells and small cells). Each of these conversions can be very inefficient, wasting about 20% of the total power the load consumes. So the fewer conversions that need to be made, the better (for both the environment and operating costs). Additionally, with 5G on the horizon, telecom power demands are increasing. In fact, power consumption is almost 2x higher for 5G networks than 4G networks. This power demand acts as a tailwind for the development of efficient telecom rectifiers that can safely handle higher voltages. Traditional telecom rectifiers typically have an output of 48V DC, but there is a new type of DC power system (the Class 4 rated power system) that enables telecom rectifiers to safely output up to 450V DC over cables that have a lighter cable gauge (close to 10x lighter, as we’ll explain later). Let’s call this the Class 4 telecom rectifier.
You can read more about Class 4 power systems in our article about them, and we’ll discuss them further in a few different telecom contexts in this article. This article also covers what a traditional telecom rectifier is, how it fits into telecom infrastructure, and the meaning of a few primary specifications for telecom rectifiers.
According to a paper uploaded on Research Gate, typical telecom rectifiers consist of a rectifier stage (AC-to-DC converter), a DC-to-DC converter, and a battery backup system. The AC to DC converter (rectifier) usually has an input of 220V AC or 380V AC (in a three-phase five wire system), and converts that to its respective voltage in DC power. The purpose of the DC–DC converter is to regulate the DC voltage input, from that higher value that came out of the rectifier, to (typically) 48V DC, as well as provide electrical isolation. Not only do rectifiers enable DC devices (such as telecom small cells) to get the DC power they need, they also provide the type of power necessary to charge backup batteries because batteries store DC power. Charging backup batteries enables telecom infrastructure to provide continuous network coverage, even in the case of a power failure.
So now that we’ve covered what a rectifier, and DC-DC converter are, the remaining elements inside a telecom rectifier are an EMI filter, and the circuitry that makes up the boost stage. An EMI filter, or electromagnetic interference filter, essentially exists to reduce or eliminate noise caused by electromagnetic interference (as well as low frequency noise from AC line voltages). According to AstrodyneTDI, electromagnetic interference can cause devices (like telecom antennas) to malfunction, crash or fail. To protect devices from damage, EMI filters block adverse interferences and allow a steady flow of DC power. The boost stage often exists in the anatomy of a telecom rectifier as a byproduct of active power factor correction (PFC). Power factor needs to be corrected because there are typically reactive power losses along cables that result in voltage drop. For example, a power factor of .9 would mean that 10% of consumed power was lost to reactive power. The boost stage corrects for this loss, and in the process boosts the DC voltage. This is typically known as a PFC Boost circuit. Check out our article on power factor if you want to learn more about it.
Traditional telecom rectifiers fit into telecom infrastructure wherever AC voltages must be converted to DC voltages in order to provide telecom cells with the DC power they need.
AC power is used in telecom infrastructure when IT equipment needs to be powered. Then, when DC telecom devices (such as macrocells or small cells) need to be powered, that power is converted from AC to DC with a rectifier. Rectifiers can be large and heavy, so it’s necessary to implement as few as possible. When you’re using one rectifier to supply DC power to multiple devices, this AC to DC conversion is known as “centralized”. In traditional telecom infrastructure (before the introduction of Class 4 power systems), DC power flowing from a rectifier to DC devices would be low-voltage (usually 48V DC), but high current, and high power. The conversion from AC to DC is necessary to power devices that require DC power, such as telecom cells. These telecom cells (both macro and micro) contain antennas, which emit network signals.
Macrocells are mounted on top of macro towers (which are usually about 50 - 200 ft. above ground). From their perch, they distribute network signals. The higher a macro tower is, the further the range of network signals. The tallest towers can provide service up to a range of 40 miles. Rectifiers are usually located at the base of towers (at cellular base stations) because they are typically heavy and clunky.
In order to power macrocells on top of tall cell towers, long lengths of cables are used. As you can imagine, power must travel pretty far to reach the top of towers, so ideally cables would be as light as possible with minimal voltage drop. This is why higher voltages would be nice. Unfortunately, in traditional telecom infrastructure these cables tend to be quite heavy because they need to have higher gauges to support a high level of current. Why do cables need to have a high level of current? These cables are only supplying low-voltages (48V DC) of DC power, and the formula for power tells us that, when voltage is lower, current must be raised to produce the same amount of power. Let me explain further.
To quote our previous article on 5G:
“According to the formula for power, lower voltages result in higher currents, for higher power levels. When there are higher currents, additional space is required within a cable for the current to move through cables without as much resistance.”
This means that higher voltages allow cable gauges to be lighter because they don’t need to support as much current.
In addition, higher voltages also reduce line losses and, consequently, voltage drop along cables. This is because, when considering both the power formula, and the resistive power loss formula together, you can see that a higher current also results in more power lost along cables, which creates heat. Heat is essentially lost energy, so less current ultimately results in less resistive energy loss.
Telecom rectifiers convert AC to DC power at the base of macro towers so that DC power can be sent to the DC devices that need it at the top. Traditional telecommunications equipment generally requires 48V DC input power. However, this isn’t the only reason that low-voltage DC is sent to the top of telecom macro towers; technicians working on telecom towers are not usually electricians, so it’s much safer for them to work with low-voltage DC, than with AC power systems (which typically start at 120V AC).
A major problem with this system is, of course, that long lengths of heavy gauge cable, carrying low-voltages, must be used to reach loads at the top of telecom towers. Class 4 power systems enable up to almost 10x higher voltages of DC power, so cable gauges can be proportionately lighter, and voltage drop can also be reduced.
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Additionally, Class 4 power systems are fault-managed, so power is stopped immediately when a fault is detected (such as a telecom technician coming in contact with a live wire). Thus, using Class 4 telecom rectifiers in telecom infrastructure would reduce cabling costs, improve safety, and reduce voltage drop along cables, while still providing the DC power necessary to power telecom equipment.
Rectifiers are also applied in telecom infrastructure when small cells are being powered. Small cells are located within telecom micro towers, which are so compact that they can be mounted on walls and ceilings. As you can see from the image below, micro towers are becoming increasingly utilized in telecom infrastructure, so it’s more important than ever to supply enough power to the small cells inside them, and to do so efficiently.
In 4G telecom infrastructure, the ratio is 4/1 with micro towers making up the smaller proportion. But now, as 5G telecom infrastructure is becoming increasingly necessary, the role that micro towers will play in network connectivity will be much greater.
Networks of telecom micro towers are called distributed antenna systems, or DAS. DAS is necessary in 5G infrastructure because 5G frequencies are much higher, and are thus less capable of traversing barriers such as walls and buildings. There are many barriers like these indoors, so to fill a larger indoor space with a network signal, a higher quantity of telecom antennas is necessary.
Cables connect each micro tower in a DAS, making long lengths of cable necessary. Similarly to the utilization of telecom rectifiers in macro tower applications, they make one AC to DC conversion and send power to DC loads. The difference is that, in DAS, they are centralized to distribute DC power to multiple DC loads from a single source. Again, long lengths of cable must be used, but in this case these long lengths of heavy gauge cable are used to connect many loads (antennas) to the power source (telecom rectifier), rather than to carry power to the top of a high tower.
Implementing a Class 4 telecom rectifier would reduce cabling costs, as well as voltage drop (energy lost along lines) for this application as well. It would do this in the same way as it would in its application for macro towers: with higher voltages and fault-management.
AC Input Ratings
A few common AC input ranges are categorized by the number of phases and AC voltages supported. A few of the common ones you’ll find are:
Example: Huawei Power solutions - range of 85V AC - 300V AC Input
DC Output Power Ratings
The total power of a rectifier is DC output voltage multiplied by DC output current.
Power ratings for telecom rectifiers vary from company to company, but these are the typical options:
Remember, the higher the wattage you choose, the higher the current will be necessary if voltage remains the same (i.e. requiring heavier gauges of cable)
Power Factor
When considering the efficiency of a rectifier, power factor is worth mentioning. Power factor is the ratio of active power (that can be used by the consumer), to reactive power. You can read more about what reactive power is on our blog, or watch this video about power factor to learn more, but essentially reactive power is a type of power lost along cables in AC power systems. For example, with a power factor ratio of 0.90, 10% of power is reactive power, or reactive power that is lost along cables.
Efficiency of AC to DC converter and DC to DC converter
The efficiency rating for telecom rectifiers can usually be pretty high. Unipower and Huawei, for example, provide equipment with an efficiency of up to 96%. This equipment only loses about 4% power that passes through the rectifier as it converts AC to DC power.
Safety features (Class 4 Telecom Rectifiers)
According to Server Technology:
“Today it is generally accepted by safety regulations and electrical code that anything operating at or below 50V DC is a safe low-voltage circuit, and -48VDC is still the standard in communications facilities serving up both wired and wireless services”
Class 4 power systems, however, exceed 50V DC, reaching up to 450V DC. So, they have different safety features that make it possible for them to safely make use of low-voltage wiring practices and lighter cable gauges. First of all, Class 4 power systems are fault-managed power systems. This means they intelligently monitor cabling between a transmitter and receiver, and shut off power if one of the defined faults occurs. See the diagram of a Class 4 Power System below for a better understanding of this.
Here’s a list of the fault conditions a Class 4 system monitors for:
Class 4 power systems actually have a double layered safety system. Fault-management is the first layer, but what if that fault-management weren’t operating correctly? The second layer of safety ensures that it is. This second layer continuously monitors the fault-management system to ensure that it’s working properly. If it detects that it’s not, the proper actions are taken to ensure this doesn’t cause any harm to the user.
Traditional telecom rectifiers have been a decent option for providing DC power to macrocells, small cells and other DC loads, in telecom infrastructure. They supply low-voltage DC power, which is adequate for 4G telecom systems and below, and they’re relatively safe for telecom technicians to work on. However, 5G infrastructure requires about 2x more power than 4G networks, and Class 4 telecom rectifiers are a solid solution to provide this power efficiently, while reducing cabling costs. Essentially, these rectifiers will play a major role in paving the way for the proliferation of 5G telecom infrastructure.
Looking for a Class 4 telecom rectifier for your project? Check out the Cence telecom solutions page to see what’s available, or contact Cence directly to provide more information on your project.
We improve the value of commercial and multifamily buildings with an intelligent DC power distribution system that's pain-free to install. It combines the benefits of low-voltage wiring practices with voltage capabilities of up to 450 Volts DC.
