In electronic products with increasing integration, multiple power supplies are often designed on the same circuit board to meet different needs. When using different power sources in combination, it is inevitable that there will be mutual influence between the power sources. This article selects a scenario for analysis and provides a reference solution.

Dual power supply issue

A customer has experienced such an application scenario during the power module application process, as shown in Figure 1 below. The customer uses two power sources to supply power to the back-end circuit and requests to switch the input power supply without interruption. During this process, it was found that the back-end circuit may be damaged. After analyzing the waveforms of each node, it was found that when the DC-DC module is powered on, a peak voltage of 13.12V is generated at the output end of the module. When the peak voltage exceeds the withstand voltage of the back-end circuit by 13V, it can cause damage to the back-end circuit.

Analysis of the problem of dual power supply combined use

We have gained an understanding of the customer's board's use of dual power switching. During use, the customer first supplies power through the TYPEC interface, then powers up the DC-DC module to establish a stable 12V power supply, and then switches to the DC-DC module for power supply. After analyzing the customer's circuit, it was found that when power is supplied through the adapter, the 12V voltage of the adapter is simultaneously connected to the output terminal of the DC-DC module. The reason for this situation may be that the 12V voltage of the adapter is applied to the output terminal of the DC-DC module, damaging the feedback loop signal of the DC-DC module, causing a spike in the output voltage of the DC-DC module, thereby damaging the back-end circuit. Verify the start-up waveform of the DC-DC module with and without adapter power supply through comparison.

Solution to the problem of dual power supply combined use

This problem can be solved from the source or Pathogen transmission: to solve the problem from the source, it is necessary to isolate the impact of adapter voltage on the DC-DC module; To solve the problem from the Pathogen transmission, it is necessary to eliminate the peak voltage generated by the DC-DC module.

Add a diode at the output end of the DC-DC module to isolate the influence of adapter voltage,

Add a voltage regulator diode in front of the back-end load circuit to eliminate voltage spikes that exceed the tolerance range.