1. Definition and classification of surges

Electrical Surge, in simple terms, refers to an instantaneous peak that exceeds a stable value. Divided into surge voltage and Inrush current.

2. Inrush Current

(1) Inrush current refers to the peak current or overload current that is much greater than the steady-state current generated at the moment of power supply connection or in case of abnormal circuit conditions.

(2) In the process of electronic design, it is often encountered that at the moment when our power supply is started, a high peak current can be clearly seen on the oscilloscope, which is about twice the normal value, up to 30A. This is because when powered on, the transformer and capacitor inductance in the power supply need to be charged, requiring a high current, which leads to the instantaneous peak current.

3. The hazards of Inrush Current

The impact of surges on sensitive electronic and electrical equipment can be classified into the following types:

(1) Destruction

● Voltage breakdown semiconductor devices
● Damaging the metalized surface of components
● Damaging the printed circuit board's printed circuit or contact points
● Destruction of three terminal dual thyristor components/thyristors

(2) Interference

● Locked, thyristor or three terminal bidirectional thyristor component out of control
● Partial destruction of data files • Data processing program error
● Errors and failures in receiving and transmitting data

(3) Premature aging

● Early aging of components and significantly shortened lifespan of electrical appliances
● Decreased output sound and image quality

4.How to suppress Inrush Current

Since Inrush Current poses so many hazards, we need to suppress this "eye-catching package" in the electronic design process and keep it within a reasonable range.

(1) Series resistor

Connect a power resistor in series to keep the current (Vin/R) within a controllable range. But there are advantages and disadvantages, as observant friends may have noticed, this design is simple, cost-effective, and only suitable for small current applications, approximately<1A.

(2) Increase RC circuit to slow down switch startup speed

By controlling the startup speed of the switch, the size of dv/dt can be reduced, thereby reducing the size of the Rush Current. However, due to the non-linear nature of the switch startup time, the Inrush Current is also non-linear.

(3) Switch for selecting Soft Start function

To obtain a linear dV/dt, a switch with a slow start function can be used. This type of switch can dynamically adjust the rise time of the output waveform by changing the capacitance value. Taking TI's TPS22975 Load Switch chip as an example, the CT pin is externally connected to a Cr capacitor, and the rise time of the output waveform varies depending on the capacitance value.

Alright, that concludes today's article. I hope it will be helpful to you.