TNY267 Power Capacity

[Pravin Gosavi]

Hello I want to drive 100x 1w leds. Leds fwd vtg is 2.5V when connected in series the whole combination fwd vtg will be 250V. And current about 400mA. Of course this set up will be on the output side of a transformer.
Suppose Input to the circuit is also 250V DC. As only 400mA current will be flowing through the IC's inbuilt mosfet Can I use tny267 IC here?
Datasheet says max power handling capacity of the IC is somewhat 20W.
But I don't think there will be any problem using it?

 

[cowboybob]

You wish to drive a 100W load with a 20W max output supply, is that correct?

Perhaps re-read the datasheet for the tny267 and its intended use.

So, as to your question:

But I don't think there will be any problem using it?

Yes, it will be a problem.

 

[Pravin Gosavi]

I am going to design the power supply. It's not a ready-made one.

 

[Pravin Gosavi]

This is the reference diagram. I think we can do it just by increasing the secondary turns and modifying feedback loop. And also by adding constant current control circuit. And some other modifications?

 

[crutschow]

I am going to design the power supply. It's not a ready-made one.

So the purpose of the tny267 circuit is to provide an isolated power supply for the LEDs?

 

[ronsimpson]

1) I don't know how you are going to use the IC. Do you have a schematic?
2) Is this part in production? The data sheet is hard to find.
3) If you use the part in the way it was designed it would be "on" for about 50% of the time. So to get 400mA out (100%) you will need 800mA (50%) from the power line. Plus there is slope to the current so you will have currents of 1.2 to 1.5A.
4) If you use the part in a DC to DC mode......well the part will not work at high duty cycles. Example 80%

 

[AnalogKid]

Can I use tny267 IC here?

No. The chip has a current limit of 450 mA and a max duty cycle of 68%. Rather than "think" it will work, run the numbers and see.

Power Integrations has dozens of parts better suited for your application, and an entire section of their site is devoted to LED applications.

ak

 

[Pravin Gosavi]

1) I don't know how you are going to use the IC. Do you have a schematic?
2) Is this part in production? The data sheet is hard to find.

Yes, I have attached the schematic in the above post. The part is available here at a very low price and its the most famous IC in "Low Cost SMPS" designers.

3) If you use the part in the way it was designed it would be "on" for about 50% of the time. So to get 400mA out (100%) you will need 800mA (50%) from the power line. Plus there is slope to the current so you will have currents of 1.2 to 1.5A.
4) If you use the part in a DC to DC mode......well the part will not work at high duty cycles. Example 80%

That means I still can use it for more power than what is read to be max in the datasheet like for 250 mA current?

 

[Pravin Gosavi]

Power Integrations has dozens of parts better suited for your application, and an entire section of their site is devoted to LED applications.

I need what is available here at cheap rate.

I will consider the option.
Thanks.

 

[ronsimpson]

Do you have to be isolated? Why?

 

[Pravin Gosavi]

No. But it's better than other methods with least no. Of components.
And How non-isolated 250VDC power supply for leds could be build??

 

[AnalogKid]

You don't need to build one. According to your post #1, a 250 V power supply is available to power the circuit.

ak

 

[dr pepper]

The tny series probably isnt the way to go, have a look at the topswitch smps ics, these go to the kind of power ratings your talking, obviously you'd need a transformer or should I say coupled inductor to isolate from the line.

 

[ronsimpson]

I will consider the option

Look at "Top Switch"

 

[ronsimpson]

How non-isolated 250VDC power supply for leds could be build??

Non isolated does not have a transformer. It usually just has a inductor. In your case you get 320 volts DC from the 220 V ac. Then buck down to the 250V you need.

I hope you know that you do not want to regulate to 250 volts, but you do want to regulate to 400mA. LEDs are current devices not voltage devices.

 

[Pravin Gosavi]

In the case how can I generate PWM for the mosfet of the buck boost converter?
I mean is there any chip to do this which can be directly powered from 250VDC (like tny IC don't need external powering circuit)?

 

[ronsimpson]

If you look at the TopSwitch, usually there is a winding from the transformer that makes a low voltage supply to power the IC. Most parts work this way.

 

[Pravin Gosavi]

Ok. Thanks.