I am trying to power a Phlatlight csm360 with 6A.
I have used the design suggested in the National AN-2041 application note for the LM3434 driver chip and built a board that should deliver the 6A. For the LED, this equates to an Vled of about 15V.
At the moment the current driver is setup for 5A, using a 12m Ohm sense resistor. According to the application note, the LM3434 tries to keep the Vsense = 60mV, thus this should give the 5A.
We are using a 100W 16V power supply. The LM3434 states that it is capable of Vout = 0.9(Vin) = 14.4V. At 5A, the LED requires about 13.8V.
I have now done some tests on the board I build. When shorting the outputs, I measure exactly 60mV over the sense resistor. This shows that the design indeed regulates the current.
But, when connecting any resistive load <3 Ohm (which will keep Vout < 15V), or when connecting the LED, I expect to see the same, ie. that the Vout is changed to achieve V = I x R with I kept at 5A). Still, the Vout just goes up until it reaches the supply voltage (16V). I then measure 70mV to 100mV over the sense resistor, equating to 6A to 8A into the load/LED.
Clearly something is wrong, as the LM3434 should keep this Vsense at 60mV.
Does anyone have any suggestion as to why my board is not regulating to the set current? The design is a copy of the circuit in AN-2041 (page 2), but using the 12m Ohm sense resistor.
Any ideas?
Thank you guys!
I have used the design suggested in the National AN-2041 application note for the LM3434 driver chip and built a board that should deliver the 6A. For the LED, this equates to an Vled of about 15V.
At the moment the current driver is setup for 5A, using a 12m Ohm sense resistor. According to the application note, the LM3434 tries to keep the Vsense = 60mV, thus this should give the 5A.
We are using a 100W 16V power supply. The LM3434 states that it is capable of Vout = 0.9(Vin) = 14.4V. At 5A, the LED requires about 13.8V.
I have now done some tests on the board I build. When shorting the outputs, I measure exactly 60mV over the sense resistor. This shows that the design indeed regulates the current.
But, when connecting any resistive load <3 Ohm (which will keep Vout < 15V), or when connecting the LED, I expect to see the same, ie. that the Vout is changed to achieve V = I x R with I kept at 5A). Still, the Vout just goes up until it reaches the supply voltage (16V). I then measure 70mV to 100mV over the sense resistor, equating to 6A to 8A into the load/LED.
Clearly something is wrong, as the LM3434 should keep this Vsense at 60mV.
Does anyone have any suggestion as to why my board is not regulating to the set current? The design is a copy of the circuit in AN-2041 (page 2), but using the 12m Ohm sense resistor.
Any ideas?
Thank you guys!
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