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LYT5226D output LED current adjustment via potentiometer

Posted by: A. Lehmann on

Hello!

I have a question regarding the aforementioned LED Driver. I am currently designing a circuit to drive LEDs, with 230VAC input, and 32V/280mA output for the LEDs. In order to better understand the function of the driver, I took a look at the DER-515 demo board for it. My question is this: in the circuit we currently use with a different driver that is EOL, we use a potentiometer to adjust the output, in order to compensate for the fact that our LEDs also have electrical tolerances. Based on the (attached) schematic of the DER-515, which resistor would I have to replace with a potentiometer to achieve the desired adjustability? My supplier said it should be R7, the DS pin resistor, however he was not sure and suggested I ask here.

I have also attached the full description of the DER-515 in case it helps.

Thanks in advance for any help and advice.

Files

첨부 파일 파일 크기
DER-515 Schematic.pdf 124.24 KB
PI DER 515 LYT 5226D.pdf 11.62 MB

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Submitted by PI-Salt on 03/06/2023

Hi,

 

Thank you for showing interest at Power Integrations and its product.

Reviewing your specification for this project,

Input Voltage: 230 VAC

Output Voltage: 32 V

Output Current: 280 mA

Output Power: 8.96 W

 

We could refer to the application note (AN65) on choosing the recommended topology for this project.

 

From AN65 on page 2, the recommended topology you should used for this design is buck or flyback.

(https://www.power.com/sites/default/files/documents/an65.pdf)

 

DER-515 is a non-isolated buck-boost design. From Table 2 of AN65 (previous link given), minimum output voltage should be greater than 48 V, which is not compatible for you design specification.

 

DER-528, a flyback design, would be a viable fit for you specification based on the recommendation of the application note. 

 

I also attached a PI XLS design based on your current specification with DER-528 as a guide.

 

After all of the design is done, page 9 or step 8 of AN65 will help you fine tune feedback and protection parameters. 

 

Thank you.

첨부 파일 파일 크기
LYTSwitch-5 Isolated Flyback Design.pdf 56.72 KB
Submitted by A. Lehmann on 03/08/2023

Hello,

thank you for your response. I have created a custom circuit that uses a buck design, which according to the document you linked is designed for 27-100V output voltage, rather than buck-boost. The input and output values are not the issue, I have a running system. My question is simply which resistor (based on the DER-515 circuit so I have something to compare to my own circuit) I ought to replace with a potentiometer to be able to adjust the output current.

Thanks again for your response, and thanks in advance for help with my issue.

Submitted by PI-Salt on 03/08/2023

Hi,

 

LYTSwitch-5 offers two ways to sense output current for proper regulation: Indirect (PSR) and Direct (SSR). The method used depends on the topology and is programmed using the RDS resistor value.

If the output ground reference differs from the input ground reference of the IC controller (e.g., in Buck or Isolated Flyback), indirect current sensing (PSR) is used, which eliminates the need for a complex optocoupler or level shifter circuitry. This method senses the signal via the RDC sensing resistor, which feeds the DRIVER CURRENT SENSE (DS) pin of the IC through the RDS resistor. The signal is then processed internally, and the interpolated value is outputted to the FEEDBACK (FB) pin.

A filter comprising CFB and RFB is used to filter the feedback signal.

In contrast, if the ground references are common between the input and output circuitry, direct sensing (SSR) is used. In this method, the RDS resistor is connected to the SOURCE pin, and the FEEDBACK pin senses the output current via the RFB2 sense resistor, which is connected in series with the load. A small low pass filter (RFB and CFB) is required to filter the feedback signal.

So for your buck design, RDS is fixed at 6k. (page 5, AN-65)

Output current could be adjusted by changing the RDC resistor, or R10 in DER-515. The voltage drop across this resistor is sensed through DS pin and the recommended average voltage drop across this sense resistor is 200 mV. (page 9, AN-65)

 

 

Thanks.