• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 513 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3409 EVM & Tungsten lamp as load

Mandar Mahajan
Intellectual 255 points
Other Parts Discussed in Thread: LM3409

hello all,

i am using Lm3409 EVM for one of my project.

The Evaluation board is doing perfect current control and changing the LED current from 0 to almost 1 Amp.

 How ever when I change the load from LED to tungsten lamp, the LM3409 stops functioning.

 I do not expect the bulb to glow at this low level current how ever I expect 1.0 Amp current to flow through the bulb. 

 Cold resistance of filament is around 0.75 Ohm which goes up as the filament gets heated.

 Pl. suggest the remedy.

  • 0
    TI__Mastermind 25500 points

    The likely reason is that with a 0.75ohm resistance and 1A of current the output would only be at 750mV which is not high enough to charge the COFF pin to its threshold and trigger the off timer. In the datasheet under the shunt FET PWM dimming section it shows to use an external voltage source to OR in when the output voltage is too low. In a case like this you will need to use some other source for the off timer so that it will switch properly.

  • 0 in reply to Clinton Jensen
    Intellectual 255 points

    Thank You Mr. Jensen for your reply. i will try this & let you know.

    however, Can i connect both the loads (LED & Tungsten lamp) to this device through a MOSFET as a switch?

    Regards

    Mandar

  • 0 in reply to Mandar Mahajan
    TI__Mastermind 25500 points

    I am not sure I understand what you mean. Is there any way you could upload some kind of schematic to show me how you want to connect them? It would also help if you can give some information on what you are trying to do with the two loads. Thanks.