Detailed explanation of the application of Boda module power supply series and parallel

The design of power supply system is a great challenge for electronic designers. They need to use limited resources and space to design flexible, efficient, reliable and competitive power supply systems in the shortest time. The power module is the best choice for designers at present. The design scheme of replacing discrete components with modular power supply is like using microprocessors to replace integrated circuits. It can complete system design and development more flexibly and quickly, shorten the time spent on product development or design changes, and save manpower and technology investment.

System power supply design is an extremely important task in application system design, which plays a vital role in whether the entire system can work properly. Therefore, when developing a system, if the power supply is designed at the end, it is often easy to increase costs and reduce reliability. Designing the power supply as a whole in the system from the beginning can save costs, shorten the development schedule and improve product reliability. Here, Shenzhen China Electronics Huaxing Electronic Technology Co., Ltd., the largest power module product agent in China, specially invites professional engineers of Broad Modular Power Supply to share with you the selection and series and parallel application of modular power supply.

Power module selection method

When selecting a power module, the power supply specifications must be determined first, mainly the power supply power, power supply output voltage, number of output ports and power supply size. When designing a system, try to use common power modules on the market. For example, Broad Power has as many as a thousand standard modules, many of which are compatible with other brands of module power interfaces. This can shorten the design and development schedule, reduce costs and improve product reliability. Therefore, when designing a system, power modules can be used in different combinations to increase output voltage, output current or backup applications, effectively reducing the types of system power supplies and improving the sharing and reliability of power modules.

Broad Power Module Series Application

In actual applications, due to board area, cost requirements, special applications and other requirements, power module products often need to work in series to obtain higher output voltages. The combination application methods are described as follows.

1. Dual-output power module:

Figure 2-1 shows a common series working application. In order to obtain a higher voltage output, the outputs of the two power modules can be connected in series and then directly connected to the load to obtain the output voltage after the two sets of outputs are added together (Vo1 + Vo2).
Broad Power engineers generally recommend that users connect diodes to each set of outputs to prevent the adverse effects caused by abnormal current paths at the output end due to the start-up time difference between the two sets of outputs. The output voltage after series connection can be added with output capacitors to reduce the ripple & noise caused by the frequency difference between the two power modules.

2. Dual-output power module:

Figure 2-2 shows the connection method of two dual-output power modules in series. Therefore, the output voltage of four groups of Vout can be obtained by adding them together. For a single dual-output power module, the startup time of the two groups of outputs is consistent, so it is only necessary to connect diodes to +/-Vo1 and +/-Vo2, as shown on the left. In the above figure, a total of 4 diodes are connected in parallel at the output end. This method is also feasible, but it is more cost-effective. The output voltage after series connection can be added with output capacitors to reduce the ripple & noise caused by the difference frequency of the two power modules.

When selecting diodes, diodes with reduced forward conduction voltage, such as Schottky diodes, should be selected, and their reverse withstand voltage should be greater than the corresponding power supply output voltage, and the forward current rating should be greater than the series load current.

Broad Power Module Parallel Application

In various practical applications, Broad Power Modules can be connected in parallel in two or more groups to achieve multiple output power for system use. Most general power modules have fixed voltage outputs. Unless the power module itself has the function of parallel operation, it should not be used in parallel. The main consideration is that the output voltage adjustment of the two power modules cannot be completely equal, so the module with higher output voltage will provide all the load current. Secondly, even if the output voltage of the two power modules is adjusted to be completely equal, the different output impedances of the two power modules and their changes over time and temperature will cause the load current of the two power modules to be unbalanced. Therefore, compared with series applications, parallel connection of power module outputs is relatively difficult. The following is an explanation of several common parallel application methods of power modules by Broad Power Module engineers.

1. Drop Resistor:

At the output end of the two power modules, drop resistors are connected in series and then used in parallel, as shown in Figure 3-1. This method mainly uses the linear voltage drop caused by the output current on R1 and R2, so that the two power modules can achieve the purpose of balancing the supply load as much as possible, avoiding the power module with higher output voltage to provide most of the load demand.

According to the actual use experience of China Electric Huaxing, this method has a low cost and is suitable for use in system applications with low precision requirements.

2. Decoupling Diode:

Figure 3-2 shows the output parallel application method using the Decoupling Diode method. The method is to connect diodes in series at the output ends of two power modules and then use them in parallel.

The principle is the same as the Drop Resistor. D1 and D2 are used to replace the role of resistors. The benefit of using diodes is that they can also be used to prevent the output voltage of different power modules from flowing back to another power module, which is required in some power architectures.

3. Current Share:

As shown in Figure 3-3, the current share dedicated IC is used in parallel. In this way, each power module itself must have the function of remote sense or trim to perform current sharing control. In this way, each power module can output current sharing, which is helpful for the life of the power module, but the cost is relatively high. It is suitable for applications with higher precision requirements.

Example of Broad Power Module Backup Application

The application of the Broad Power Module backup function is mainly to connect two identical module outputs in parallel through a diode, which can double the output capacity and improve the reliability of the power system. The backup system is mostly represented by N+1, that is, N power modules provide the rated power required by the system, and at least one more power module is used as a backup to prevent the system from being unable to operate continuously when the power module fails, so as to maintain the normal operation of the system. If it is matched with a power module that allows hot plugging and an alarm circuit with the corresponding output, the power module is placed on a detachable busbar. When a fault occurs, the power module can be replaced in real time, and the power system will have very high reliability.

1. OR-ing Diode:

In the output circuit of two or more power modules, each diode is connected in series and then in parallel, so that when a single module fails, the other modules can continue to provide power to maintain normal operation of the system. The diode should have a low forward voltage drop (Low Vf) to reduce conduction loss.

2. OR-ing FET:

The application and function of OR-ing FET are the same as OR-ing Diode. The main difference is that OR-ing FET uses MOSFET instead of Diode to reduce conduction loss. Using OR-ing FET requires additional control circuits, which is more expensive.

EMI Decoupling of multiple power supplies

In a power system, if multiple power modules are used at the same time, and the input uses the same power supply, in order to prevent mutual interference between two or more power modules, the formation of EMI problems that are not welcome in the system, and even harmonics that cause system malfunctions, at this time, L1, C1, L2 and C2 can be added between the front end of the power system and the EMI filter to reduce the mutual interference between the power modules.