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PMP6024: Auxiliary Power Supply and Dimming input recognition

Part Number: PMP6024
Other Parts Discussed in Thread: LM2596, , LM3409

I want to use this design for one of our upcoming project. I want to control dimming using WiFi or BLE or any other external RF-SOC. I have following requirements.

1. I need 3.3V or 5V power supply. If in this design the auxiliary power supply is available, can somebody help me to find out the pin from which I can take the 3.3V or 5V power out? If no, can i use LM2596 as buck converter to get it from ISO_15V pin or do you suggest any other chip?

2. Dimming input identification: Is EN pin of U15 used for dimming? If yes, It had been directly connected to +50V. Will it not damage the IO (which will be used for PWM generation) of PWM generating circuit? If no, please help me to identify the dimming inputs in this design.

3. What are the output voltages and currents available at VLED1 & VLED2. As this design says '60W, 2-string', does it mean 60W output at each string totaling to 120W or is it 30W at each string?

4. If I want to change VLED outputs to 20W each at both strings, what changes I need to make in the design? 


Best Regards,


  • Hello,

    1) Due to cross regulation the accuracy of using the main transformer may to be good enough. Using a simple buck converter from one of the bias winding would work better, or you could add a winding that regulates a little higher than 3.3V or 5.0V and linear regulate it down to what you need.

    2) Yes the EN pin can be used for PWM dimming. The voltage levels are stated in the datasheet and can be driven with 3.3V logic or 5V logic. If you plan on using this pin with logic circuitry you don't want it pulled up to Vin, use a pull up to the logic voltage you are using.

    3) This design is 60W total, 30W each string. The design was intended to show Class 2 use which means under 60V on the output. This one is set to 50V so the LED strings connected have to be less than 50V otherwise the buck converter cannot work. This information is all in the PMP6024 report.

    4) You can change R79 and R89 or change Viadj on the LM3409. This changes the current going to the LEDs. The power will be the current times the overall LED stack voltage which is not regulated, only the LED current is. The design equations are in the LM3409 datasheet. You also do not have to change the output power capability of the flyback since it is regulating voltage and you power requirement is less.

    Best Regards,