I want to make a low-power isolated switching power supply, 100V to 2.5V output about 80 mA, is it feasible to use LNK361?

huo_hu

I want to make a low-power isolated switching power supply, 100V to 2.5V output about 80 mA, is it feasible to use LNK361? [Copy link]

 

 

This chip is quite commonly used. I wonder if anyone knows the conversion efficiency, or if there is any other simpler method. Without considering the input voltage fluctuation, can the efficiency reach 85%?

maychang

"Can the efficiency reach 85%?"

Based on the 3.3V voltage regulator in the picture, the efficiency will definitely not reach 85%.

huo_hu

maychang posted on 2021-10-19 18:34 "Can the efficiency reach 85%?" Based on the 3.3V voltage regulator in the picture, the efficiency will definitely not reach 85%.

It needs to be improved. Reduce the number of turns to lower the voltage. Just ensure 2.0~3V.

huo_hu

LNK363 seems to be simpler

maychang

huo_hu posted on 2021-10-19 20:22 It needs to be improved. Reduce the number of turns and lower the voltage. It will be fine if it can guarantee 2.0~3V

For such a low voltage output of 2.5V, the forward voltage drop of the secondary rectifier tube cannot be ignored. Assuming the tube voltage drop is 0.4V, the efficiency of this part is already 0.862, which is very close to 85%.

maychang

huo_hu posted on 2021-10-19 20:22 It needs to be improved. Reduce the number of turns and lower the voltage. It will be fine if it can guarantee 2.0~3V

"It needs to be improved. Reduce the number of turns to lower the voltage. Just make sure it's 2.0~3V."

Generally speaking, the lower the output voltage, the more difficult it is to achieve high efficiency.

tagetage

The isolation efficiency cannot be achieved, the output current is too small, and it is very difficult to achieve even without isolation.

huo_hu

The output adds a middle tap and two half-wave rectifiers

maychang

huo_hu posted on 2021-10-20 10:49 Output with an intermediate tap and two half-wave rectifiers

"Add a middle tap to the output for two half-wave rectifications."

Your circuit is a flyback converter. How can a flyback converter have "two half-wave rectifications with a center tap"? Besides, "two half-wave rectifications with a center tap" cannot improve efficiency.

se7ens

The duty cycle is too small. Please check whether the minimum duty cycle of the control chip meets the design requirements.

huo_hu

maychang published on 2021-10-20 12:35 "How about adding a middle tap to the output for two half-wave rectification?" Your circuit is a flyback converter. How can a flyback converter "add a middle tap to two half-wave rectification"?

Output is not common ground

maychang

huo_hu posted on 2021-10-20 17:55 The output is not shared

"Output is not shared"

If the output is not required to share a common ground, then there is no way to "center tap two half-wave rectification". Center tap, the two windings must have a common point, which is the center tap.

maychang

huo_hu posted on 2021-10-20 17:55 The output is not shared

"Output is not shared"

Besides, “output is not shared” cannot improve efficiency.

huo_hu

Thank you for your guidance. I will try again and ask you if I have any questions.

soso

huo_hu posted on 2021-10-22 21:53 Thank you for your guidance, I will try again and ask if I have any questions

Looking forward to the sequel.

huo_hu

soso posted on 2021-11-2 10:13 Looking forward to the follow-up.

Later this plan was not adopted because the isolation voltage of this power supply was not high enough. In addition, the switching power supply EMC was difficult to use, so we still used the most primitive transformer.

soso

huo_hu posted on 2021-11-3 17:09 Later, this solution was not adopted because the isolation voltage of this power supply was not high enough. In addition, the switching power supply EMC was more difficult, so the most primitive transformer was used.

Okay, got it.