TNY280 dual-voltage design

Posted by: Richard Wright on 06/16/2010

I put this on the PI Expert forum without response, so I am re-posting here.
Thanks.

I used the PI Expert software to generate the attached dual-voltage design. The first voltage is for a string of 20 leds @ 350mA (approx 64 volts) the second is a 9.0v @ 20mA to be used for logic. Could you please verify the opto-isolator connection is correct? The documentation generated didn't show this very clearly. Also, if you could check my capacitor voltage-ratings. This is for universal voltage input. I have attached my schematic. If you need the PI expert file I generated, please let me know. Any help is appreciated. Thanks!

-Richard Wright c/o Lumasmart

Files

LS450PS2_0.pdf (24.47 KB)

Comments

You need to add 100 ohm resistor in series with zener D5 to limit current into opto LED. Also zener sense point should be before final LC filter -- that is, attach zener to cathode of D4 which is the unfiltered output. This will allow converter to operate with greater stability margin.

everything else looks OK...

Thanks for the info!

Hi,
Just wanted to be sure this is what you meant. Thanks again!

Hello,

The circuit seems to be working well as far as voltages. However, when I was using the PI-Expert, I selected LED type circuit. I guess I was ussuming a constant-current supply, and not constant voltage. If I connect 20 LEDs in series, I get more than 450mA to start, and it slowly rises to about 508mA then it starts to flash. If I go to 21 LEDs, the current starts at about 285mA then rises slowly. I beleive the slow rise is due to the LEDs heating up, as I do not have them heat-sinked other than to the pcb. I varified with a resistive load of about 194-ohms, and it seems to hold steady at 67volts, 350mA. Is there a way that I could modify the circuit for constant-current? The 9-volt tap is great. Thanks.

Richard Wright c/o Lumasmart

Hi,
Per your last post, it mentioned to put a 100-ohm resistor in series with the zener diode to limit the current to the opto-coupler, which I understand. However, is there a correct way to determine the proper value for this resistor? I see in the PI expert software it only lets a value of up to 97-ohms.
Any info would be great. Also, what voltage would be considered appropriate for the cap in the clamping circuit? I have a 250v, 2.7nF device, is this okay?
Thanks.
-Rick