LNK 413 led driver design

Thanks for posting here, and especially for including transformer designa nd schematic (from PI Expert forum).

Is the output stable ie the design is regulating and the LED are constantly on but the current is too low?

Assuming the LEDs are on but current is too low there are a couple of possibilities that come to mind.

In LinkSwitch-PH output current is a function of the V pin and FB pin current. If the output current is too low then either the V pin current is too high or the FB pin current is too low. It's more likely to be the FB pin so let's start there.

Does the output current change with line voltage?

Check the bias winding voltage (across C6), measure at 100 VAC and 220 VAC and tell me the measured DC voltage (using a DVM is fine).

I'm automatically notified when you reply so I'll response ASAP once you let me know your results.

Cheers

PI-Chekov

100V - Bias voltage = 18.3V , LED current 550mA

150 - 200 V - Bias voltage = 18.4 - 18.5 V , LED current fluctuating ( 700 - 800 mA)

230V - Bias voltage = 18.5 LED current 680mA

most of the time i have notified that at lower voltages ( 100 - 150) LED driver is working smoothly and when further increased audible noise starts and output current drops .

thanks
ajith

Bias voltage looks fine (I was concerned the bias winding may have been wound backwards making a forward rather than a flyback winding. Had it been configured as a forward winding the voltage would change proportionally with input AC).

How is your PCB layout around the V pin?

The V pin is high gain and high impedance. If any of the power traces or components connected to the drain are close to the V pin components or traces then you could see the problems you reported.

Could also be the same issue around the FB pin. I just wonder if noise is making the FB pin hit the 210 uA skip threshold - this could cause audible noise.

Cheers PI-Chekov