LNK6404 or an alternative module

Posted by: viktor.wagner on 10/26/2017

Hello dear PI team,
I just try a switching power supply with our converter (translation 1: 1)
and your Linkswitch LNK6404. I have made this with fixed frequency (Schmitttrigger, C and R), but because of the high EMI disturbances I wanted with your LNK6404 by frequency jittering minimize the disturbances.
Now to the question: Since I have no additional winding on the transmitter, I do not know how I connect the FB and BP Pins.
Maybe you have an alternative module that fulfills this function.
I have a circuit diagram attached.

PS:I do not want the FB PIN connect over Optokoppler and secondary coil, since
it is not possible for reasons of space. May I can connect the FB pin by means of voltage divider (over 2 resistors) and the primary coil (of the transformer). See IG_7757.jpg

Thanks in advance and nice weekend

Files

IMG_7756.jpg (114.7 KB)

IMG_7757.jpg (107.19 KB)

Comments

Hi Victor,

You will have poor output load regulation, having no primary side regulation via an extra winding or no feedback taken from the output side by means of the optocoupler.

You may just connect the 1uF capacitor at the bias pin without additional supply from the extra winding. The supply of the IC will take from the drain pin during off time of the Mosfet. The disadvantage is that you will get low efficiency.

Regards,
PI-Picard

Hi Picard,
thank you for the quick support.
I've already tried that. The LNK6404 then clocks with a very low
Frequency of about 360Hz. With this frequency very little power is transmitted.
Is there no way to get higher Frequency and in addition to activate the frequency jittering?
Thanks in advance and have a nice weekend

Hello,
how can I feedback the LNK6404 via optocoupler.
I have not found any examples in the data sheet. Is it even possible? Or do you have another LinkSwitch that could do it?
PS: I have very little space on my assembly and the following conditions:
- Vin about 60V
- transformer (ratio 1: 1, without additional winding),possibly via optocoupler
- Vsec 16V (for DALI)

Thanks in advance

Hi Viktor,

There are no examples using optocoupler because that is the advantage of our solution. To eliminate it all secondary control circuitry and have simpler primary side control. May I ask if you would require more space if you use optocoupler plus the feedback control circuit? Is it still possible to try with an additional winding? The advantage is that you can provide external bias circuit to supply the device for better efficiency and less no load power consumption. If you want, you can try using optocoupler and see the response.
Further, you need to measure the drain current and see if it is current limiting at such a low DC input voltage. What is your output power requirement?

Regards,
PI-Picard