MP4033 NTC shutdown does not work when dimmer is attached

[gfuchs]

According to the data sheet the NTC input pin should follow this curve.

I find that the driver I am tested does work this way when no dimmer is attached in the AC line. However, if I add a standard triac dimmer the minimum current that I can achieve is 50% of the maximum even with the NTC pin pulled to ground. Is there any reason that the NTC pin should behave differently with and without a line dimmer?

[gfuchs]

As a follow up, the problem only occurs with leading edge (triac) dimmers, with trailing edge dimmers (ELV) the NTC pin operates normally.

[Saquib.FAE]

@gfuchs

I find that the driver I am tested does work this way when no dimmer is attached in the AC line. However, if I add a standard triac dimmer the minimum current that I can achieve is 50% of the maximum even with the NTC pin pulled to ground. Is there any reason that the NTC pin should behave differently with and without a line dimmer?

Hello @gfuchs,

The NTC pin should operate as per Fig 19 irrespective of the type of dimmer used. May I know what type of triac dimmers are you using and what is the value of Rntc used in your application?