Micro-power DC-DC power modules are widely used in circuit design with multiple advantages such as high integration, high reliability and simplified design. Although its application circuit is simple and easy to operate, it often encounters some common problems in application. In this paper, the power module common application problems and how to troubleshoot a detailed analysis.

Micro-power DC-DC power supply module is favored by many electronic designers with multiple advantages such as high integration, high reliability and simplified design. Although the power supply module has simple application circuit and simple operation, it often encounters some common problems in application. In this paper, the common application problems of power supply module and how to troubleshoot are analyzed in detail, hoping to help the designer's power supply module selection.

FAQ 1: Output ripple noise is too large

Reason 1: When the module is in use, the load is a dynamic load, which makes the peak-to-peak value of the module output voltage larger, but note that this is not ripple noise.

When the load current is periodically changed, the peak-to-peak value of the output voltage of the module will become larger. This is a transient quantity, but is sometimes mistaken for ripple noise. Therefore, when a power supply module is used to supply power to multiple circuit units, for a circuit with periodic load changes, a π-type filter needs to be added at the front stage to reduce the interference of transient changes in this part of the circuit to other circuits.

Reason 2: oscilloscope ground problem

When testing the ripple noise of the power supply output, the ground clamp and ground wire of the oscilloscope and the module output pin form a loop, which is similar to the antenna receiver and will introduce other noise. If the test environment interference is large, this noise will also be introduced by the oscilloscope, affecting the results of the ripple noise test.

And usually the ground of the oscilloscope probe we bought is connected to the ground wire inside the oscilloscope, which has weak immunity to power frequency interference and is easy to introduce interference noise. Therefore, in use, it is very good to ensure that the oscilloscope probe floats (isolate the power supply of the oscilloscope, or directly use the battery-powered oscilloscope) to reduce the interference introduced. If the power supply of the measurement object is also floating, this is better, so that it will not cause changes in circuit characteristics and increase the output noise of the module.

FAQ 2: After the module is started, the output voltage is low

Reason 1: the input has anti-reverse circuit

Cause 2: output wire impedance is too large or voltmeter connection is not standard

When using the power supply module, we are testing the output voltage and often seek to directly test the voltage at the input end of the power supply circuit. However, since the impedance between the output terminal of the module and the input terminal of the power supply circuit is too large, the measured value is lower than the actual value. Therefore, when testing the output voltage of the power supply module, the voltage between the output pins of the module should be measured instead of the voltage at the input of the power supply circuit.

Reason 3: When using the module, the required power of the power supply module is not accurately estimated, so that the module is in an overload start or overload working state

For example, ZY_FKES-3W a power module with constant voltage input and unregulated output, the rated power is 3W, that is, the power range used by the module cannot exceed 3W. ZY0505FKES-3W module under 5V input, when the output 400mA, the output voltage is about 4.98V; When the output is 600mA, the output voltage is about 4.88V. If it is overloaded, the output voltage will be lower. As the load increases, the output voltage decreases, and this constant voltage input is the characteristic of the unregulated output module.

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