MOSFET redundancy module YR80.241 with voltage drop of only 50mV

1 Introduction

24V DC Power Supply Voltage failure usually means major safety hazards or economic losses. Reliable and uninterrupted supply of 24V power around the clock is becoming more and more important, especially as power systems become more intelligent and processes become more complex and efficient. It is not only applicable to industrial systems, but also to many other fields.

Redundant power supply systems are the most common applications in the telecommunications industry, process industry and power plant base stations. In areas such as traffic control systems, tunnel monitoring and access control systems, redundant working methods are becoming more and more common and important. PULS has developed two new redundant modules for high-power applications in this field. Together with the standard 24V power supply, a high-power redundant system can be built. As shown in Figure 1.

Figure 1 PULS redundancy module

2 Current Status of Redundancy Technology

With the help of low-loss MOSFET technology , PULS has for the first time achieved the goal of building a 40A redundant system with just one redundancy module. Two separate modules are no longer required for each power supply in this power range.

In the simplest scenario, redundancy means two power supplies in parallel, each of which can independently supply the load. This solution is called 1+1 redundancy. See Figure 2.

Higher output currents use an N+1 redundant system. In the example of a 120A load current, four 40A units operate in redundant mode. If one unit fails, the remaining three power supplies can continue to safely provide 120A current.

Figure 2 40A 1+1 redundant system

3 Technical features of PULS redundancy modules

Typically, redundant power systems are single power supplies connected in parallel. Since standard power supplies usually do not have decoupling diodes at their output ports , these units must be connected using redundancy modules. This means that even in the event of a short circuit or defect in the power supply output stage, the system remains redundant.

Redundant systems require monitoring the functionality of each individual power supply to ensure early detection of faults and to initiate maintenance procedures. For this purpose, the DC-OK signal of the power supply can be used.

3.1 “Decoupling diode” with a voltage drop of only 50mV[1]

The epitaxial diodes or Schottky diodes in standard redundancy modules cause a voltage drop of (500-800) mV[2] between input and output. Depending on the load circuit, the power losses can be high and lead to heating problems. In the new YR40.241 (40A) and YR80.241 (80A) redundancy modules, the conventional diodes have been replaced by MOSFETs for the first time. At first glance, this does not seem to be a major breakthrough, because such "synchronous rectification" is already widely used in various power supply output stages. After installing external redundancy modules, unexpected operating conditions such as short circuits, reverse polarity or load feedback must be taken into account, which are not easy to solve at all.

If a short circuit occurs in the load or cabling, the supply voltage drops and no voltage is actually available at the redundancy module. However, the MOSFETs in the redundancy module must remain powered, so that the power loss of the short-circuit current is lower. If the power supply of the MOSFET fails, the entire current will flow through the "body diode" of the MOSFET, causing the power loss of the MOSFET to increase by about 15 times. To avoid this, a patented circuit is used to generate the appropriate supply voltage from the lowest residual voltage. This method is particularly important in the event of a short circuit when the power is turned on, or in the event of a reverse input voltage. The new circuit also allows these situations.

The advantages of the MOSFET redundancy module are self-evident. The low on-resistance of the MOSFET makes the voltage drop much lower than when using a diode. At an output current of 40A, the difference between the input and output of the YR80.241 is only 50mV. As shown in Figure 3. When using a traditional diode module, the voltage drop is at least 500mV. Similarly, the power consumption of the diode increases by at least 10 times, and a large heat sink is required for cooling. As shown in Figure 4. The MOSFET redundancy module YR80.241 has a power loss of only 2.7W at an output current of 40A. This includes not only the power loss of the MOSFET, but also the power loss of the terminals, internal wiring, and required circuits. No heat sink is required.

Figure 4 Power loss curve of redundant module

3.2 80A MOSFET Redundancy Module without Heatsink

The YR80.241 redundancy module contains two 40A inputs and one 80A output, and can be overloaded by 160% in a short period of time. This allows a 1+1 or N+1 redundant power system with an output current of 40A to use only one redundant module. Due to the low power loss, there is no need to install a heat sink internally, and the width of the device can be limited to 46mm. As shown in Figure 5. The module prevents short circuits, avoids reverse polarity, and can operate at full power between -40°C and +70°C. The maximum voltage of feedback-type loads such as brake motors is even allowed to reach 40Vdc. In order to be suitable for global use, we are planning a comprehensive international certification package that includes ATEX (Explosion-proof Directive) certification in addition to many safety certifications.

For smaller output currents, the YR40.241 redundancy module has a maximum output current of 40A and a width limit of 36mm.

Figure 6 Redundant system dimensions

Similarly, the design of a 20A redundant system was realized using the YR40.241 redundancy module and a 20A power supply.
In addition to these two high-current redundancy modules, PULS also offers redundancy modules with diodes for smaller and medium output circuits. These modules are available with or without integrated monitoring functions. The monitor recognizes the output voltage of the power supply below a fixed threshold and opens the signal contact at the appropriate time. This function is crucial if the power supply itself does not have a DC-OK signal.

4 Conclusion

Due to the use of new MOSFET technology, the power loss of the redundant module is further reduced, and 40A 1+1 redundancy can be achieved with only one redundant module, which greatly saves design costs and reduces power loss. In today's product design with environmental protection as the concept, this technology will surely shine and be widely used.

PULS has a wide range of products and usually does not require complex custom solutions. Engineers can rest assured that they can use well-designed and thoroughly tested standard products.

When designing a redundant system, the recommended methods for reliable redundant operation are as follows.

⑴ Use a separate input fuse for each power supply.

⑵ If possible, connect the power supply to a different phase or main circuit.

⑶ Use three-phase power supply to ensure functional safety when one phase fails.

⑷ Be sure to use redundant modules or decoupling diodes.

5. All power supplies must be monitored individually. If a fault occurs, it must be detected and corrected as soon as possible. For this purpose, the DC-OK signal of the power supply can be used.

⑹ Set the output voltage as evenly as possible. If the device has a "parallel use" function, set it to "parallel use" mode.

Figure 5 Appearance of YR80.241

3.3 Powerful product series - QT40.241 and YR80.241

Until recently, the space required for a single 40A power supply on the DIN-rail exceeded that required for a fully redundant system. A fully redundant system consists of two three-phase 40A power supplies (QT40.241) and a YR80.241 redundancy module. Here a width of 266 mm is sufficient. In single-phase systems, the QS40.241 power supply can be used. This results in a total width of 296 mm. See Figure 6. The higher partial load efficiency and the "parallel use" mode of the new 40A power supplies are particularly advantageous. This mode ensures that the load current of the individual power supplies remains unique, which benefits the reliability and service life of the entire system. Integrated input fuses, active power factor correction (PFC), a wide temperature range and high power and current reserves (60A for 4 seconds) are just a few of the many innovative features of the new QT40 and QS40 power supplies. The integrated DC-OK signal for monitoring the power supply function ensures that faults are detected as early as possible and maintenance procedures can be initiated.

Figure 3 Relationship between voltage drop VON and output current IT of YR80.241