Soft Starter (Inrush Current Limiter) for AC/DC Loads

[Hesambook]

Inrush current/Switch-ON surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Inrush current is much higher than the load’s steady-state current and that’s the source of many problems such as fuse blowing up, load failure, load’s lifetime reduction, sparks at the switch contacts … etc. I tried to address this problem with an easy, however effective solution. I have introduced two circuits for both AC and DC loads.

References

Article: https://bit.ly/2AlBcyB

[1] DB107 Datasheet: https://www.diodes.com/assets/Datasheets/products_inactive_data/ds21211_R5.pdf

[2] BD139 Datasheet: https://www.onsemi.com/pub/Collateral/BD139-D.PDF

[3] DB107 Schematic Symbol and PCB Footprint: https://componentsearchengine.com/part.php?partID=771938

[4] BD139 Schematic Symbol and PCB Footprint: https://componentsearchengine.com/part.php?partID=971726

[5] CAD Plugins: https://www.samacsys.com/library-loader-help

 

[d123]

Hi,

They're nice circuits, practical and useful. Nice work. Have you considered doing a DC one with a linear ICL circuit, using a current source, capacitor and MOSFET? They are also useful when inrush current level and/or required rise time fit together...

 

[Hesambook]

Hi,

They're nice circuits, practical and useful. Nice work. Have you considered doing a DC one with a linear ICL circuit, using a current source, capacitor and MOSFET? They are also useful when inrush current level and/or required rise time fit together...

Thanks. may I ask you to explain a bit? You can control the current limit (inrush level) by changing the power resistor and also the delay for the relay activation

 

[d123]

Hi,

I just meant that in certain cases, the solution I mentioned is also an option, no switching in and out of devices and it is smaller: (two NPNs, one PMOS, two resistors and one capacitor) when a small voltage drop, the PMOS Rds(on), is not an issue that will affect circuit functionality. Every solution has pros and cons.

 

[Hesambook]

Hi,

I just meant that in certain cases, the solution I mentioned is also an option, no switching in and out of devices and it is smaller: (two NPNs, one PMOS, two resistors and one capacitor) when a small voltage drop, the PMOS Rds(on), is not an issue that will affect circuit functionality. Every solution has pros and cons.

for DC load isn't it?

 

[d123]

Hi,

Yes, DC.