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What problems does the switching power supply have in the application? How to solve?
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What problems does the switching power supply have in the application? How to solve?

What problems does the switching power supply have in the application? How to solve?

2019-07-26

Low-power power supplies are widely used in the electrical and electronic industry. In the process of application, some power failures, such as poor start-up, low output voltage, and overheating of the module, often occur. problem? This article will be announced for you.


·Low output voltage

If the output voltage of the power supply is too low, the latter circuit will not work properly. For example, in the microcontroller system, the load suddenly increases, which will lower the power supply voltage of the microcontroller and cause the microcontroller to reset. This will be the whole system level. The circuit brings a devastating blow, which will lead to a chain reaction of a complete failure. Is the output voltage too low for these reasons?

The output stage is connected in parallel with multiple loads. After normal operation, a load requires a large transient current, causing the voltage to be pulled down instantaneously, thereby affecting other parallel loads;

If the output line is too long or too thin, the line loss is too large, so that a small voltage drop occurs between the lines, and finally the voltage of the power module is low when the output voltage of the power module reaches both ends of the real load;

The voltage drop of the anti-reverse diode is too large. Generally, the forward voltage drop of the diode is between 0.2 and 0.6V. If the output of the power module is 5V, the voltage drop generated by the diode with high on-voltage drop will cause the voltage drop. The voltage of the latter circuit is too low to work properly;

The input filter inductance in the peripheral circuit of the module is too large, resulting in the internal resistance becoming larger, and the current 扼 is used to enhance the production. When the load at the rear stage suddenly becomes heavy, the current supply is not high and the voltage across the load is low.

·Solution

At the output and a large capacitor or switch to a higher power input power supply;

Adjust the wiring, increase the cross-sectional area of the wire or shorten the length of the wire, reduce the internal resistance. If the power module has the Trim function adjustment, the output voltage can be increased to offset the voltage drop caused by the line loss;

Switch to a diode with a small conduction voltage drop;

Reduce the filter inductance value and reduce the internal resistance of the inductor.


·Module fever is severe

The power module has energy loss during the voltage conversion process. The heat generated by the module causes the module to heat up, reduces the conversion efficiency of the power supply, and affects the normal operation of the power module. However, under what circumstances will the power module heat up more seriously?

The linear power module is used. Due to the internal circuit structure of the linear power supply, the power conduction voltage drop is large, and the loss generated inside the linear power module is larger under the same output power;

Over-loading of the load, beyond the scope of application of the data sheet, so that the internal critical device temperature rises;

Excessive ambient temperature or poor heat dissipation;

Other large heat source heat transfer.

·Solution

Add a heat sink when using a linear power supply, or choose a high-efficiency switching power supply;

Replace the module with higher output power to ensure 70%~80% load derating;

Reduce the ambient temperature and keep the heat dissipation good.


·Large output noise

Noise is a key indicator to measure the strengths and weaknesses of power modules. In the application circuit, the design layout of the peripheral components of the module will also affect the output noise. Which factors have a greater impact on the output noise?

The power module is too close to the main circuit noise sensitive component;

The decoupling capacitor is not connected to the power input of the main circuit noise sensitive component;

Difference frequency interference between power modules of single output in a multi-channel system;

Ground treatment is unreasonable;

The noise at the input of the power module is too large, unprocessed, and is directly coupled to the output of the power module.

·Solution

Keep the power module as far as possible from the main circuit noise sensitive component or module and the main circuit noise sensitive component;

A 0.1μF decoupling capacitor is connected to the power input of the main circuit noise sensitive component (eg A/D, D/A or MCU);

Eliminate difference frequency interference by using a multi-output power module instead of multiple single output modules;

Use a remote grounding point to reduce the ground loop area.



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