der263

Posted by: brano on 04/22/2012

Hi
I am designing a led bulb circuit by the der263 design but I am going to dim by using microcontroler. Also a active load will by controled by the microcontroler.
If the circuit is running without leds but with 330ohm load on the output the output oscilating like short circuit protection. But there is only 330ohm on the output. Should I conect 330 ohm after start up?

Brano

Comments

The active load is not the same as connecting 330ohm at the output. Pls refer to page 12 of the report on the operation of the active load.

If you open the load, it will go to OVP mode of the circuit.

Hi
OK, the active load is not conected if 1-10 signal missing(by der263).
To symplify my try there is not pwm block and active block in my circuit.
If the output is open and without a load there is about 40V. How can I reduce it to 35V? Decreasing VR3 nominal voltage does not help me.

I intend to replace pwm block and active load block by microcontroler. There will be 3bits a/d converter instead off active block. Is it possible to replace
active load? It will not be so quick like native analog circuit?

Brano

It is already shining. Active load helps to dim into low levels. 8 levels of active loads only degradeate a linearity. How can I decrease open state voltage?

Brano

If you want a very tight ovp like the 35V that you required, yo need to add a dedicated secondary ovp using an optocoupler. The transistor side of the opto will replace Q3, and the diode side is in series with a zener diode in the secondary tied across the output.

What is a function of VR3 diode?

Brano

VR3 is the diode that sets the OVP. However since its sensing the bias winding, its not as accurate as the dedicated ovp I previously mentioned above. This Vr3 will be on the secondary side in series with the opto diode if you decided to pursue the accurate secondary ovp.