85 - 530 VAC input, 5 VDC / 70mA output power supply

Hi Vukadin,
Below are my suggestions.
My questions are next:
- Which option is better, InnoSwitch or DER-58 with some other PI IC (and which would you recommend for this design)?
Use Similar to DER-58. Innoswitch IC have higher power capability thus it is more expensive on your design. To Chack your design you may want to visit our design tool on the link below.
https://piexpertonline.power.com/site/login
- Is there going to be a problem with minimum on time?
If you would be using on-off control it wont have any minimum on time issue since it would act like on a burst mode.
- Is there any commercially available transformer to be used in this design?
-If you mean a pick-and-place transformer, none.
- Is there going to be audible noise due to a high number of cycles skipped?
Audible noise shouldn't be a problem since you will be drawing a very low power

Regards

Hi,
Thank you for prompt response.
Regarding IC for DER-58 design, which is better to use LNK304 or LNK3204? Are both of them intended for use in new designs? As far as I saw, they are almost the same (with LNK3204 having higher breakdown voltage).
Is there DER-58 eval board that can be purchased?
Regards,
Vukadin.

Hi Vukadin,
LNK3204 is the improve version of LNK304 and LNKSwitch-TN2 such as LNK3204 are thus recommended for new design. For evaluation board please contact local distributor/FAE so that they may help you on your requirement.

Thanks.

Hi,
Thank you for information.
We will use LNK3204, like I assumed.
I have two more questions, have you tried to use high voltage film capacitors for designs like this (high input voltage, low output power) in input stage instead of electrolytic capacitors and how do they worked?
Regards,
Vukadin

Hi vukadin,
Yes it will be ok as long as the minimum capacitance is twice the maximum output power if you are using 85Vac input. Ex. 0.35W x 2 = 0.7uF you should be using at least 0.7uF of input cap.
Regards

Hi,
That's great! Thank you for information.
Regards,
Vukadin.

Hi,
We have made power supply according to DER-58. Changes are (we used what we have already in house):
- RF1: Regular 10R/3W resistor,
- C1-C4: 4u7/400V,
- D9-D12: P6KE200,
- D14: BZX85C15,
- Q1: P3NK60ZFP,
- D15: UF4007,
- Feedback circuit: According to DI-124, with VR6: 2PD4V3.
When turned on power supply maintains regulation for short period of time and then starts reseting due to a high temperature on LNK. Measured temperatures are next:
- LNK304 turns off on 70 C and then turn on on 50 C.
- On transformer ferrite core 55.4 C is measured (before reset).
- On MOSFET Q1 46.5 C is measured (before reset).
Do you have any suggestion what can be a reason for this behavior.
Regards,
Vukadin.

Hi,
It looks like something is oscillating when we take a look on D pin of LNK304 (take a look at the picture in attachment). Any idea?
Regards,
Vukadin.

Hi Vukadin,

It seems behaving anything but a flyback waveform.

About the temperature protection, are you sure it is the over temp protection that is keep on resetting? Since 70degC is very low even if you have thermal resistance on the plastic material of the LNK304 IC. Specs wise it would turn of at 135degC with 75degC hyterisis. Meaning, if it Over temp protect at 135degC the IC will restart only when it already cools to around 60degC.

Hi,
I agree that waveform is pretty strange.
I suppose that temperature protection is reseting chip, since every other protection have autorestart time set to 800 ms (according to datasheet). Here, there is at least 20 seconds between restarts.
Also, it looks like some other component (in feedback part, or somewhere else) has strong temperature variation because output voltage falls from ~5.15 to ~ 4.9V during process.
Regards,
Vukadin.

how is the device heat-sunk?

Hi Easy Peasy,
There is no heatsink on device. It is cooled by wide plane connected on source pins. I will extend this and repeat measurements.
Regards,
Vukadin.

Hi all,
I have extended source plane, but no improvements, still have same behavior. Any other ideas?
Regards,
Vukadin.

Need to know more about your transformer - and a picture of the power supply would help too

Hi Easy Peasy,
Transformer is made according to PI DER-58 (Wide-range Flybak using LNK304). Wires and core used are mentioned in document. Bobin is with 10 pins instead of 8, and we used other insulating tape. Coil used is Ferroxcube E13/7/4 3F3 (https://www.tme.eu/en/Document/37bfe69b814ef7b7eac1fcc463270891/e1374.pdf) on which we made air gap of ~350 um in center part.
I have made power supply on test board for now. Pictures are in attachment.
Regards,
Vukadin.

It does look a bit like your Tx is incorrectly terminated (phasing of output wires)

What is your Lp?

Hi,
What is the latest update, have you already find a solution?
You may want to put this on a PCB as your current board are prone to noises.
I have also attached application notes for LNKTN for design guide to improve your design.

Hi,
We have ordered transformer samples from transformer manufacturer and will make PCB these days. Then, we will test again.
Regards,
Vukadin.

Hi all,
We got transformer samples and tested on test board. Power supply works OK in range from 100 VDC input up to 600 VDC. It provides desired output (5V/70mA) and temperatures of LNK and transformer when input is 600 VDC are ~74 C and ~70C (when placed in plastic enclosure).
Regards,
Vukadin.

Hi,
That's good to hear.

Regards.