Low-SideBuck-Boost on LNK3202
Good day.
I am trying to make a converter based on LNK3202, but it does not produce the required voltage level. I use the Low-SideBuck-Boost -Optocoupler Feedback topology page 3 AH70. If you replace LNK3202 with LNK3206, everything works as it should.
I use an LTV-816 optocoupler, a US1M diode, a BZV55С3V9 zener diode, a 2200 μH choke.
Comments
Required output voltage 5V, output current 40mA.
Output voltage is:
- about 2.5V with a resistor Rz = 470 Ohm
- about 4V without Rz
Hi,
The power limit might have been reached. Can you send the schematic with component parts, and input specifications? Does the same result happen when tested using higher input voltage?
Thanks
Good day, thanks for your answers.
1. Input voltage AC 85-265 V 50 Hz.
2. The input is a half-wave rectifier.
3. The converter is currently without load.
4. Increasing the input voltage does not give positive results.
Attachment | Size |
---|---|
LNK3202.pdf | 16.33 KB |
Hello,
There might be a problem in the feedback. You can try reducing R42 to 220 ohms to supply 5mA to the optocoupler.
Thanks
Hello.
With a resistor R42 100 Ohm also does not work. The output voltage is 2.8 V.
Earlier, I conducted an experiment and reduced the value of the R42 resistor from 2 kOhm to 100 Ohm. Then I removed it completely. The result is described in the post above.
Hi,
Have you tried testing it at no-load?
Also, can you send the waveform during start-up at no-load and full-load so that see if auto-restart is observed?
Thank you.
Hello,
I wrote earlier that I am testing the converter without load (no-load mode).
Attached to the message are 2 photos waveform of the output voltage.
Attachment | Size |
---|---|
load 50 mA.jpg | 744.96 KB |
no-load.jpg | 759.12 KB |
Hi Rokali,
Good day!
To summarize the specification
85Vac - 265Vac
5V / 40mA Load
Input is Half Bridge Thanks
The concern is:
LNK3202 is used Output is not regulating
LNK3206 is used Output is OK
With the above experiment using LNK3202 and LNK3206, this is my perspective.
LNK3206 has a high current limit (ILIM) which can charge the output within 50msec.
LNK3202 has a low current limit (ILIM) which cannot charge the output within 50msec.
At start up Vo should be in regulation within 50msec. If not, Output will shutdown and retry again after 1.5sec.
Since the output capacitor is quite high and ILIM and ILIM is low,
Please try to reduce the Output capacitor 100uF to 10uF.
Regards
PI-CHLOE
Good day, PI-Chloe!
Thanks for your answer.
I tried the LNK3202 with a 10 uF capacitor. The converter still does not supply the required voltage.
I also tried the LNK3204 microcircuit on the same board. Everything works as it should.
Hello,
May I know what the required output voltage and current is? What is the produced output voltage when LNK3202 is used?
Thank you.