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LED Driver ICs Forum Discussions

User21125
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What's the difference of TLD5099EP dimming between using PWMO and opening PWMO ?
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fausto_borg
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Moderator 10 likes received 10 sign-ins 5 solutions authored
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For an LED driver the difference is on the waveform of the output current.
Using PWMO connected to and NMOS the system is able to produce very sharp current waveform at output, while if the PWMO is left open the the current waveform is prolonged even after the PWM signal goes to low level.
The reason is that without the dimming element the output current is not interrupted by the PWM modulation and it flows into the load until the output voltage of the DC-DC is higher than the forward voltage of the LED string.
This means that with a dimming element the system is able to replicate at output also very low duty cycle PWM modulation that are not possible without (the system has to recharge the output voltage to have the desired output current).

You can find more information on the PWM features in the datasheet
Other information related to LITIX Power devices can be found in the webpage

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fausto_borg
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Moderator 10 likes received 10 sign-ins 5 solutions authored
Moderator
For an LED driver the difference is on the waveform of the output current.
Using PWMO connected to and NMOS the system is able to produce very sharp current waveform at output, while if the PWMO is left open the the current waveform is prolonged even after the PWM signal goes to low level.
The reason is that without the dimming element the output current is not interrupted by the PWM modulation and it flows into the load until the output voltage of the DC-DC is higher than the forward voltage of the LED string.
This means that with a dimming element the system is able to replicate at output also very low duty cycle PWM modulation that are not possible without (the system has to recharge the output voltage to have the desired output current).

You can find more information on the PWM features in the datasheet
Other information related to LITIX Power devices can be found in the webpage
fausto_borg
Moderator
Moderator 10 likes received 10 sign-ins 5 solutions authored
Moderator
Here in the below picture I also highlight the main difference on the produced waveforms of output current and voltage.
4943.attach
As reported in the previous reply, the main advantage using the PWMO dimming device is the sharp waveform of the current.
You can also look that the output voltage stays constant, because the dimming element prevent the discharge of the output capacitor on the LED string.
User21125
Level 1
Welcome! First question asked First reply posted
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Thanks for your detailed explanation,that helps a lot. sometimes leave the PWMO open just for the cost-down.
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