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taewan
Level 2
Level 2
5 questions asked 10 sign-ins First like received

TL431.JPG

hello. I am Kim studying in Korea and I am designing and experimenting with a half-bridge LLC resonant circuit. The current circuit has 380V~400V input and 30V, 50A output.
A problem occurred while doing feedback control during the experiment. As shown in the attached circuit, a feedback control circuit was constructed using TL431 and an optocoupler.
The problem is that whenever the DC input voltage changes, the output voltage rises proportionally and the output voltage is not adjusted to 50V at all.
Please help me...

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1 Solution
Guruprasad_A
Moderator
Moderator
Moderator
25 likes received 250 sign-ins 50 solutions authored

Hi @taewan ,

Thank you for posting in the Infineon community.

The schematic of the feedback control circuit using TL431 and an optocoupler is acceptable. (Value must be adjusted during testing).

  1. Please check the resistor values for R35 and R36. Since the switching frequency is determined by the equivalent of these two resistors.
  2. Please verify the R48 value. Typically, it is in Mohms.

We are still checking the schematic. Can you give us more information so that we can analyze the issue?

  1. Voltage at Vmc and CS.
  2. LG pin waveform
  3. Vcc voltage value.

Regards, 

Guruprasad A

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1 Reply
Guruprasad_A
Moderator
Moderator
Moderator
25 likes received 250 sign-ins 50 solutions authored

Hi @taewan ,

Thank you for posting in the Infineon community.

The schematic of the feedback control circuit using TL431 and an optocoupler is acceptable. (Value must be adjusted during testing).

  1. Please check the resistor values for R35 and R36. Since the switching frequency is determined by the equivalent of these two resistors.
  2. Please verify the R48 value. Typically, it is in Mohms.

We are still checking the schematic. Can you give us more information so that we can analyze the issue?

  1. Voltage at Vmc and CS.
  2. LG pin waveform
  3. Vcc voltage value.

Regards, 

Guruprasad A

0 Likes