Did you connect an LED load during power up? If not, then the output voltage will go up until the Zener diode at the output clamps it to 100 V. However, this would cause a failure on the Zener diode.

( I initially did not connect a led load . Some time zener may be burnt due to that.)

Later I connected a led load (12V) with a 5k6 (5W) resistor in series without a zener.
I changed the FB resistor to 15 ohm , 27 ohm, 39 ohm values but still the output voltage is around 230V-240V . is this OK?
Is this regulation done using the IC or the Zener?
What if zener is not used. Is zener compulsory?

When you connect an LED load, don't put a series resistor with the LED load. The power supply operates in CC mode. It is the one that will set the output current. When you connect a 12 V LED load, the output should clamp to 12 V. Zener diode is not compulsory, but it's highly recommended in case there is an output open fault so it can protect the output capacitors.

Thanks PI-Crumb for replying my post.

I constructed the circuit in the application note using DOT board except the smd IC LYT0006 as shown in attached herewith. See the attachment.

I got 80mA across the LED load. 14 leds. ( 14 = 2 X 7 0.5W LEDs).

Voltage across the Led = 19.5V . Izen = 0 mA. (Zener used = 22V)

FB resistor = 22 ohm (carbon film cheap one ) .

According to these results
the electrical power consumption across LED = 19.5V x 0.08 = 1.56W

Is this results OK ?

How can we change the wattage as 3W , 5W , 7W, 10W with LYT0006D ?

Hi ubotheju,

Based on previous discussions, we can assume that the design you are currently using is from:
RDR-378 7W Non-Dimmable, Non-Isolated Buck LED driver. Microsoft Word - RDR-378 7W 85V 82mA A19 Non-Dim Non-Iso Buck LYT0006D Rev1.0 10-04-13.doc (power.com)
 

This design you are currently using is rated for 85V LED, 82 mA, 7W rated and based from the query above it seems that you have a different LED load. 

It would be beneficial if we could know your rated Vout, Iout so we could use the PIXLS tool according to your specific design needs. Please see attachment below which is design for 1.52 W (19V, 80mA) to serve as an example to your design.

To adjust for the power you need to design as per AN-60 - LYTSwitch-0 Design Guide | Power Integrations. Essentially, you need to design the minimum inductance needed for your specific design and design the feedback resistor that would cater that power. All the design guide is described inside this document. 

PIXLS tool is an easy to use and will help you know the correct values needed for your design. Thank you.

Hi  PI crumb, 

I managed  to design  7W led driver   with  about 140mA , 45V ( 3.1V x 14 (led)=  43.4V   )  with your advice.  However it need to be further tested for the performance.

I set the feedback resistor to  13.3 ohms.

What is the best current for LEDs.  150mA ?

What is the best  LED type (3V, 6V , 9V ...)  for lyt0006D ? 

Also  I  started working with  lyt1604 and had  similar problem and  started another PI session.

Thank you

Upeka Botheju

hi,

The current is dependent on the type of LED you use. Please check the specs of the LED you are using and the current should be derated based on that. As for the voltage, the higher voltage would mean lower current. LYT0006D has a current limit of 0.35 A so to be able to use it on your design, the output current should be less than that. Please run your design through PI Expert Online to be sure. https://piexpertonline.power.com/pixls/design/index