Only 1% of engineers know that the application design and quality of power modules are equally important

Why do you need a DC-DC module power supply?

DC-DC isolation module power supplies are mainly used in distributed power systems to achieve isolation and noise reduction, voltage conversion, voltage stabilization and protection functions for the power system. The functions of using DC-DC isolation module power supply are as follows:

First, the module power supply adopts an isolation design, which can effectively isolate the impact of common-mode interference from primary-side equipment on the system, allowing the load to operate stably.

Second, different loads require different power supply voltages. For example, control ICs require 5V, 3.3V, 1.8V, etc.; operational amplifiers for signal acquisition require ±15V; relays require 12V, 24V; and the bus voltage is mostly 24V. Therefore voltage conversion is required.

Third, the bus voltage will have line losses during long-distance transmission, so the voltage when it reaches the PCB board level is low, and the load requires a stable voltage, so a wide voltage input and a regulated output are required.

Fourth, the power supply needs to protect the system load and itself from damage under abnormal conditions.

How to choose high reliability DC-DC module power supply

Adopt mature power topology

The design of the power module should use mature power topology as much as possible. For example, the constant voltage input DC-DC power module of 1W to 2W chooses Royer circuit, while the wide voltage input series chooses Flyback topology in many cases and forward topology in some cases.

High efficiency over the entire load range

High efficiency means lower power loss and lower temperature rise, which can effectively improve reliability. In practical applications, the power supply will choose a certain degree of derating design, especially today when the power consumption of the load IC is getting lower and lower, the power supply may work under light load most of the time. Therefore, high efficiency within the full load range is a very critical parameter for power system reliability, but is often ignored by power supply manufacturers. In order to attract customers based on the parameters in their technical manuals, most manufacturers often achieve high full-load efficiency, but the efficiency is low at 5% to 50% load conditions.

Extreme temperature characteristics

The geographical area where power modules are applied is very wide, ranging from tropical heat to severe cold similar to Russian winter. Therefore, the minimum operating temperature range of the DC-DC module is required to be -40°C to 85°C, and some can do better. For example, Jinshengyang's constant-voltage R2 generation 1W to 2W can operate at -40°C to 105°C. If used in automotive BMS and high-voltage busbar monitoring applications, the operating temperature needs to be -40°C to 125°C. Jinshengyang's CF0505XT-1WR2 can operate at 125°C.

Extreme temperature testing is the best way to test the reliability of power modules, such as high temperature aging, high temperature & low temperature live performance testing, high and low temperature cycle impact testing, and long-term high temperature and high humidity testing. Formal power supply development will go through the above tests. Therefore, whether there is such testing equipment has also become the basis for judging whether a power supply manufacturer is a copycat manufacturer.

High isolation, low isolation capacitance

Medical products require extremely low leakage current, and power electronic products require as little parasitic capacitance as possible between the primary side and the secondary side. These two industries have a common requirement, which is to require as high an isolation withstand voltage as possible and as low an isolation capacitance as possible to reduce the impact of common mode interference on the system. If used in the medical or power electronics fields, it is recommended to choose a power module with an isolation capacitance of less than 10pF for 1W to 2W DC-DC, and for wide voltage products, try to choose a power module with an isolation capacitance of less than 150pF.

EMC characteristics

EMC performance is the guarantee for the normal and safe operation of electronic systems. Currently, the electronics industry has put forward very high requirements for the EMC performance of products. Customers often complain that poor EMC handling leads to system resets, restarts or even early failures. Therefore, excellent EMC Features are the core competitiveness of power modules.

Reliability of power system application design

The reliability of the power supply itself is important, but in fact, due to the complexity of the working environment of the power supply system, no matter how reliable the power supply is without reliable system application design, the power supply will eventually fail. The following introduces several common power system application design methods and precautions.

Redundant Design Tips

In situations with high reliability requirements, it is required that the system cannot be powered off even if the power module is damaged. At this time, redundant power supply can be used to improve system reliability. When one power module is damaged, the other module can continue to provide power.

In the figure, it is recommended to use low voltage drop Schottky diodes for D1 and D2 to prevent the voltage drop of the diode from affecting the work of the back-end system. In addition, the withstand voltage value of the diode should be higher than the output voltage. This method will produce additional ripple noise and requires an external capacitor to reduce the ripple or add a filter circuit.

Derating design

As we all know, derating design can effectively improve the working life of the power supply, but if the load is too light, the performance of the power supply will not work at its best. For example, Jinshengyang DC-DC module power supply is recommended to be used within the load range of 30% to 80%, at which time the performance will be optimal in all aspects.

Reasonable peripheral protection design

There are many application industries for power modules, and the application environmental requirements are also not the same. Because of its universal design, DCDC module power supplies can only meet common requirements. Therefore, when the customer's application environment requires harsh requirements, appropriate peripheral circuits need to be added to improve the reliability of the power supply.

Thermal design

About 15% of the damage to industrial-grade power modules is caused by poor heat dissipation. Power modules are developing in the direction of miniaturization and integration. However, in many applications, power supplies work continuously in a closed environment. If the heat accumulation cannot If it spreads out, the components inside the power supply may be damaged due to excessive thermal stress. Common cooling methods include natural air cooling, heat sink cooling and forced cooling fans. Some experiences in thermal design are shared as follows:

Cross ventilation for power modules. For power modules that rely on natural convection and thermal radiation to dissipate heat, the surrounding environment must be convenient for convection and ventilation, and there must be no large devices around to facilitate air circulation.

Placement of heating components. If there are multiple heat sources in the system, such as multiple power modules, they should be as far away from each other as possible to avoid mutual heat radiation transfer and overheating of the power modules.

Reasonable PCB board design. The PCB board provides a way to dissipate heat, and more consideration should be given to the way of heat dissipation when designing. For example, increase the copper area of the main circuit, reduce the density of components on the PCB, etc., and improve the heat dissipation area and heat dissipation channels of the module. For example, the power module should be placed vertically as much as possible to dissipate the heat upward as quickly as possible; if the DC-DC module is If placed at the bottom of the PCB, the upward heat dissipation will be blocked by the PCB, causing the product to accumulate heat that cannot be dissipated.

Larger package size and heat dissipation area. For power supplies with the same power, if possible, try to choose a larger package and a radiator with a larger heat dissipation surface, or use thermal conductive glue to connect the power module shell to the chassis. In this way, the power module has a larger heat dissipation area, the heat dissipation will be faster, the internal temperature will be lower, and the reliability of the power supply will naturally be higher.

Matching design and safety design. The input wiring of the power supply should be kept as straight as possible to avoid forming a loop antenna to attract external radiation interference. At the same time, the input and output lines need to be kept at an appropriate distance in accordance with the safety requirements of UL60950 to avoid voltage failure. Furthermore, wiring under the power supply chassis is prohibited, especially signal lines and the electromagnetic wires of the power transformer, which will interfere with the signal.

Another thing that designers need to pay attention to is that they need to pay attention to the stagger between the primary power supply and the secondary power supply, as well as the frequency multiplication of the power supply and the system operating frequency, to avoid system matching problems between them.