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High-Voltage Constant Current LED driver w/ DC input

Posted by: JEO on

I'm trying to design a LED driver, but after analysing PI controllers couldn't find an adequate solution.

The specs are:

Vin = 70V to 140Vdc

Vout = around 130V (depends on LED string)

Iout = 250mA

Any help would be a blessing. Thanks for yr patience.

JEO

评论

Submitted by PI-Wrench on 02/16/2022

What sort of features/solution were you looking for that you couldn't find in the PI lineup? The power requirement is modest, so a fair number of products could suffice for this application.

Submitted by JEO on 02/16/2022

Thanks for yr attention.

Special features are a low component count and transformerless converter for driving 20W LED power.

In the present phase, I'm using a LNK3207P, buck-boost with a constant current output of 170mA, driving a LED string reaching around 60V.

With Vin=70Vdc, trying to increase the output current (or more output voltage with a string with more LEDs) will cause thermal problems (controlled ambient temperature of 40ºC). The device starts thermal protection and the LED string flickers at regular time intervals.

A small heatsink glued to the LNK3207P improves to a maximum of 200mA@60V.

Probably I'm trying to put the device to the maximum.

The LYT1604D seems to be a more powerfull choice for transformerless designs, but it misses buck-boost topology, as far as my limited knowledge understood.

As I need 20W of LED power, my solution now is to use 2 converters of 10W (170mA@60V), sharing the input PI filter, for driving 2 LED strings.

But a better/smarter solution would be very appreciated.

Thanks,

JEO

 

Submitted by PI-Wrench on 02/17/2022

I had a look at the product catalog - there are solutions that could provide a boost-derived constant current circuit, but they would require an inductor with an extra winding - hence, a transformer of sorts. Attached is a rough-cut schematic showing a possible solution using  a device from the TOPSwitch-JX family, to give you a rough idea of the overall topology and estimated parts count. Let me know if this could possibly work for your requirements.

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Submitted by PI-Wrench on 02/17/2022

I may have figured out a way to run without the bias wdg using TinySwitch-4. Let me know if you are OK with the overall topology, and we can explore that option.

Submitted by JEO on 02/22/2022

Thanks for yr concern and for the clever ideia of using a TOPSwitch-JX in a buck-boost topology. And sorry for my delay.

Due to the lower on-resistance of the MOSFET in the TOPSwitch-JX family compared to TinySwitch-4, I prefer to try it. And TOPSwitch (E-version) is easier to heat-sink.

As I have no problems with no-load consumption and efficiency is not the major concern, will supply the transistor's opto-coupler with a zener//cap linked to Vin by a pull-up resistor (wasting about 1W). This way I avoid the bias winding and can use a common drum coil.

Hope this week to have time to experiment yr idea with some devices I bought sometime ago. I will let you know about the results.

Thanks again,

JEO

Submitted by PI-Wrench on 03/01/2022

This design I showed in previous posts may require a 400V output diode rather than 200V, depending mostly on the voltage for the LED string you are trying to drive..