Incandescent lamp on XC23

Guillaume Fournier 6 years ago in Expansion modules / XC2x updated by Gustav Widén (System support) 6 years ago 1


I am using a DOUT LS on XC23 to drive a 12V incandescent bulb on an instrument panel.  In steady state, the lamp draws 85 mA.  I am getting an overload on this output when I try to activate the lamp.  I was able to temporarely solve the problem by using a 22 ohms in series with the load.  So I believe the problem is the inrush current of the lamp.  The instruction book of the XC23 clearly states that the LS DOUT "are designed to drive small loads, e.g. lamps and buzzers".  The example even shows a lamp being driven by a LS DOUT.

Can you explain if I'm doing something wrong.  If not, is there any fix available to solve this issue ?



In think you are right in your guess that the inrush current is too high. 

In the XC23 user manual Appendix A , this is how we specified it:

The maximum load 300 mA per channel is the limit we set for each channel, it is intended as a continuous current. 

This gives some margins to the overload limit for an individual DOUT on the XC23, the detection limit is somewhere between 0.5 to 0.9 A. This protective function reacts within microseconds. 

Say that your incandescent lamp has an inrush current about 15 times higher than steady state, this would be about 1.2 to 1.3 A, causing the overload detection to react.  

What you could try is to bank four channels together to get to a higher load. 

The max combined load 850 mA that we set for the four channel combinations is due to thermal limitations, so I don't think this  should be as much of a problem for an inrush current.