Hi Alex,

May I know why do you need the LYTSwitch-4313 as a voltage source? LYTSwitch-4 is a primary-side constant current controller. What is you application? Thank you for your interest in Power Integrations product.

Hi PI-Zek,

The application is a small form factor isolated modular led driver for architectural lighting.

I am trying to create an offline led driver that can act as a voltage source for a constant current buck converter, while still allowing it to operate on a phase cut dimmer.

A constant current buck converter allows for a larger variation in forward voltage of leds. We can detect the input phase and then dim the buck accordingly. This would allow for a more modular design.

For example, if the voltage supply was good to 30 watts (30v @1A as a supply to the CC buck converter), we would have the ability to drive any led between 1-29v at almost any current up to the max power (limited by the CC buck converter to 3A), while being able to dim with a traditional phase cut dimmer and maintain a good power factor.

See attached image.

Let me know if that makes sense.

Thanks,

Alex

Hi Alex,
I have a LYTSwitch 4 reference design for CV application but not TRIAC Dimmable. You need to add some components to be able to work at CV operation.

Please find attached file for your reference.

Hi PI-Martok,

If I understand correctly, it will not dim (on its own) based on a TRIAC input but will it operate as a CV supply with a TRIAC input? So no matter what the TRIAC is doing to the line voltage, the output of the CV supply will be relatively the same?

Dimming will be controlled by separate hardware.

Also, the attached reference design appears to be non-isolated? Is it an isolated design or non-isolated?

On a side note, it doesn't necessarily have to be the LytSwitch-4 controller. That just happens to be what I am working with at the moment for another project. If there is a different controller that can act as a CV supply with a TRIAC input, I am open to using that.

Thanks,

Alex

Hi Alex,
The feedback will adjust the duty cycle to regulate the voltage as the the RMS voltage go lower during TRIAC dimming. But I'm not sure how far the feedback regulate the output. The IFB range is limited but probably enough for single input range PSU.

The topology of the attached reference design is buck-boost(non Isolated). The added components for CV operation is the same when using flyback topology. You can refer to the application notes and PI Expert only only for flyback design.

Hi PI-Martok,

Thank you for the responses.

Would this kind of solution also work with a TinySwitch-4? Can a TinySwitch-4 operate on an TRIAC waveform?

Also is the architecture of the attached schematic correct for the flyback version of the CV? I still need to tune the component values but I want to make sure its right.

For the transformer design, PIXI designer does not offer a CV option for the LytSwitch-4. Is it still possible to use PIXI for the transformer design? If so, what would need to change from the CC version?

Thanks,

Alex

Hi Alex,
TinySwitch-4 cannot operate in TRIAC waveform. It needs bigger capacitor to operate and the PF is too low.
Your schematic looks good. You can refer to the reference design I attached previously for the calculation of component values.
You can use the PI expert online for CV or CC. Just input the required CV output voltage and output current. set the current limit mode at "FULL".

Hi PI-Martok,

Should I ignore the error messages that come up? See attached.

Thanks,

Alex

Hi Alex,
There is an error opening the file that you attached. Can you give the output specification and I will try to do the PIXL design for you. Thanks

Hi Pi-Martok,

Output specifications:
Vo = 30V
Io(max) = 1000mA
Vin = 85-132Vac

Thanks,

Alex

Hi Alex,
Please see attached design based from PIexpert online. I use LYT4316 device and PQ2020 core for your 30W flyback PSU. Transformer wire gauges need to optimized for efficiency and winding area.

https://piexpertonline.power.com/site/login

Hi PI-Martok,

Thank you very much for your help and quick responses.

Alex