Why does the output voltage of the power module become low?

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Why does the output voltage of the power module become low? [Copy link]

Why is the output voltage of the power module with a nominal output voltage of 5V actually only 4.8V? Here we will introduce the reasons and solutions for the low output voltage of the power module. Generally speaking, the module will be functionally tested before being mounted on the board to verify whether the voltage output of the module is normal. The power module outputs voltage but the voltage is lower than the nominal output value, which is a common problem encountered during the test process. There are two reasons for this situation. One is that the power module is defective or damaged, and the other is the problem of usage. The following will focus on the situation where the output voltage of the power module is low due to usage. 1. Low input voltage Low input voltage is the most easily overlooked situation. When there is a problem with the output, we should first check whether the input is normal. For power modules with fixed voltage or wide voltage input, when the input value is low, the output value will also be low. Of course, this situation is limited. For a specific module, when the input voltage is too low, it will not work and there will be no output voltage.

Figure 1 Input nominal voltage and operating voltage range

2. Output overload Output overload means that the load working power is greater than the rated output power of the power module. Under overload conditions, the output voltage of the power module is significantly lowered. Taking ZY0505FS-1W as an example, when the load current increases to 300mA, the output voltage is only 4.5V. Continuous overload will affect the working efficiency, stability and heat dissipation of the power module, resulting in a reduction in the service life of the module. If the output voltage is too low due to overload, you need to increase the output power of the power module. You can choose a 2W or 3W module.

Figure 2 Output overload

3. Large routing impedance The power module output and the load must be connected by a PCB routing. The longer the routing and the narrower the routing, the greater its equivalent resistance. The equivalent resistance can be considered to be connected in series in the working loop of the load, which will play a voltage divider role, thus causing the voltage at both ends of the load to be less than the output voltage of the module. In addition, in addition to routing problems, there are many other situations that play a similar role, such as poor contact of solder joints leading to an increase in equivalent resistance, and oxidation or corrosion of the line leading to an increase in equivalent resistance.

Figure 3 Equivalent resistance causes voltage drop

4. Anti-reverse diode The AC and DC parts of many products are not on the same board. In production or end-customer use, it is inevitable to involve plugging and unplugging the power connector. In order to prevent hardware damage caused by reverse connection in this process, a diode is often connected in series. Taking a diode with a voltage drop of 0.7V as an example, the voltage between b1 and b2 will be 0.7V lower than the voltage between a1 and a2. This is the case of low input voltage discussed above. It can be solved by selecting a tube with a lower voltage drop or directly increasing the voltage between a1 and a1.

Figure 4 Anti-reverse diode

5. Summary The power module can enable engineers to avoid many problems in power supply design. Choosing a suitable power module can not only shorten the product development cycle but also improve the market competitiveness of the product.