Electronic – Why does a spark occur when an SMPS is connected to the load circuit

batteriesbattery-chargingpower electronicspower supplyswitching

I am using a 36VDc SMPS as a power supply. A spark is generated when I connect 36V with my load circuit.

Specification:

  • Voltage source: 36VDc
  • Current consumption: more than 3A

I want to know why a spark is generated when I attach my load circuit, and how can I reduce the spark.

I have tried some RC circuit solutions given for arc suppression circuits but I can not identify how can I use those solutions.

Is there another way to reduce the sparks?

I tested with a 1545CT Schottky diode to put at the beginning of my circuit as mentioned in this answer, but the solution isn't useful in my case.

@Manumerous, can you guide me for which type of MOSFET I have to use in my circuit with configurations to avoid a spark?

Best Answer

This is a very common occurrence if your load contains a large capacitor bank. The problem is that if the voltage over a capacitor changes fast (as when you connect the load to the power supply), this results in very large currents. This can be seen by the following differential equation for the capacitor current:

$$I_c(t) = C \frac{dV(t)}{dt}$$

Unfortunately this is exactly the case when you connect your load to the power supply. In this case your capacitors will draw a lot of current (which is often called the inrush current)

You can reduce this by limiting the current with a large enough resistor. This approach is the simplest, but adds additional losses through the resistor and increases the input impedance. A better Option would be to use an NTC Thermistor in that case. These resistors have a negative temperature coefficient, which means that there resistance decreases when they heat up. Therefore, the resistance of the NTC Thermistor becomes very low after it is warmed up by the current passing through it. This achieves a power loss that is lower than when a fixed resistance is used. You can find some information about NTC Thermistors here: How to Use NTC Thermistors for Inrush Current Limiting

Alternatively you could add an electric switch (like a MOSFET for example), which ramps up the voltage and therefore eliminates the spark. An in depth discussion about that topic as well as schematics for how to connect the MOSFET can be found here: StackExchange Electrical Engineering: P-Channel MOSFET Inrush Current Limiting

Furthermore also the geometry of the connector can influence the stark. There are dedicated anti-spark connectors which help reduce it or ensure that the spark can not come in contact with the skin.

Related Topic