Inrush Current Limitation: An Innovative Circuit Solution
This circuit undoubtedly falls into the category of “Why didn’t I think of that earlier?” It addresses a common challenge encountered by anyone working with electronics, which is the necessity or desire to control the inrush current of a substantial load. In the past, this task was accomplished by introducing a robust resistor into the supply line’s series and deploying a contractor (or a relay equipped with supplementary electronics) to promptly bypass the resistor.
This bypass was activated by a delayed gate signal originating from an RC network that featured an upstream series diode. However, this approach had a notable drawback: it suffered from the fact that triacs with unipolar triggering exhibited different trigger sensitivities for positive and negative half-waves. Consequently, the proposed type (TIC106) typically triggered at a gate current of 60 µA. This feature enabled resistors R1 and R2 to possess relatively high values.
Adjusting Trigger Delay with Resistors and Capacitor
The trigger delay in this circuit is determined by a combination of resistors and capacitor C1. This delay is contingent on the tolerances of the components and might extend to several hundred milliseconds. It’s imperative to use a 5 W resistor for R3 since it needs to dissipate a substantial amount of power during this brief timeframe. The author has frequently employed similar series circuits as soft-start mechanisms for incandescent lamps, especially ones with low cold resistance.
This application becomes critical, especially in scenarios like camping, where using an inverter to convert 12 V DC to 230 V AC can lead to high inrush currents with a 100-watt incandescent lamp. These currents can pose startup challenges for the inverter, even with a 300-watt rating, and can potentially damage the lamp. Additionally, when relatively large transformers are in use, they can generate significant peak currents during switch-on, thus impacting the circuit’s elegant simplicity. The choice of R3’s value should be tailored to the specific intended use or desired inrush current level.
Understanding the Role of Resistors in Electronic Circuits
Resistors, fundamental electrical components, serve the vital function of limiting or regulating the flow of electrical current within an electronic circuit. Moreover, resistors can be strategically employed to provide a precise voltage for active devices such as transistors, enhancing their utility in various circuit configurations and applications.