Will 48V be the new 24V?

If the DC supply voltage is increased from 24V to 48V, then the total current will be halved and the cable losses will be quartered. This means that four times as many loads could be run from the same supply cable.



The main reasons why 48V was not chosen as a standard industrial supply voltage instead of 24V were that 48V lead-acid batteries were simply too big and heavy and that it was harder to find DC/DC converters and regulators that could operate from such high input voltages. Even 24V supplies are often dropped down to an intermediate bus voltage of 12V to supply the point-of-load converters that power low voltage 1V/2.5V/3.3V circuitry.

Recently, there have been two developments that have changed the whole game plan and made 48V supplies significantly more attractive.

The first game-changer is GaN HEMT. This is a new type of switching transistor that can switch much faster than silicon-based technologies. If a 100 kHz DC/DC buck converter is used to efficiently step down a 48V supply to 1.2V, then the mark space ratio will 40:1. Add a load regulation capability of 1% and the switching transistor must cope with a PWM signal with less than 2.5ns jitter. This is at the limit of conventional switching regulator technology, but well within the specification of GaN transistors, making 48V-to-1V converters a practical possibility.


The second game changer technology is mild hybrid electric vehicles. A mild hybrid is like a standard car with a fuel-burning engine and a 12V lead acid battery but also has an extra 48V lithium-Ion battery and an electric drive.

The 48V battery can be used to power the car purely electrically for the first hundred metres or so after moving off, thus a smaller and more efficient engine can be used without harming the acceleration. This also means in heavy stop-go traffic, the fuel burning engine will not be running.

Thus automotive manufacturers can be the latest energy efficiency standards for urban traffic conditions without having to redesign the whole vehicle.


The 48V battery also allows for higher peak electric loads than is possible with a 12V system, so that the air conditioning, power steering and turbo charger can all be electrically powered at will and not constantly absorbing power by being mechanically connected to the engine. With some clever control algorithms, the overall efficiency of the vehicle can be significantly increased.

What this all means for industrial applications is that 48V lithium-ion batteries will soon become mass-produced, low-cost items. As lithium-ion batteries are also more compact and lighter than an equivalent lead acid battery, they are ideal as a back-up supply storage element for 48V systems.

The major difference between a 48V lead acid and 48V lithium-ion storage battery is the allowed voltage levels. The traditional telecoms standards for a 48V input DC/DC converter supply are based on old lead-acid battery chargers with a 18-75V output voltage range. Lithium-Ion battery packs must not be over-charged nor deep-discharged to avoid damage to the cells.
The limits are laid out in the LV148 norm:


LV148 48V Lithium-Ion Voltage levels:


Therefore, a DC/DC converter designed to operate from a 48V supply with Li-Ion back-up does not need to operate over a 4:1 input voltage range. A 3:1 input range (20-60V) is perfectly adequate. Furthermore, the old telecoms standard allowed input voltages of up to 75VDC which is higher than the Safe Extra Low Voltage (SELV) limit of 60VDC. If an industrial installation can be made SELV then there are big savings to made in the cabling, installation and equipment costs, which is why Power-over-Ethernet (PoE) is limited to 56VDC, for example.

In conclusion, a DC/DC converter that operates over a 3:1 input voltage range of 20-60V will cover 48V lithium-Ion battery voltages, well regulated (±10%) DIN rail standard power supplies of 24V, 36V and 48V, and PoE supply voltages.

RECOM offers the RS3-Z series which is a miniature 3W DC/DC module with up to 3kV isolation for the new 48V supply standard. Regulated output voltages of 3.3V, 5V, 9V, 12V, 15V, ±3.3V, ±5V, ±12V and ±15V are available to power a variety of sensors, monitors, ADCs, DACs and isolated data busses from a 20V – 60V supply. The converters are sealed against moisture and dirt, operate from -40°C up to +85°C ambient temperature and are UL and EN certified, making them ideal for industrial applications.

RECOM also offers a range of single-phase AC/DC DIN rail mounted power supplies with 48V outputs with 120W, 240W or 480W output power. The units can deliver up to 150% over-power to supply high-start up loads and can be paralleled to increase the output current. They are fully UL/IEC and EN certified for use in industrial applications.

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