UCC256403: Audible noise from system during no load

Eswara rao Gottapu

Prodigy 30 points

Part Number: UCC256403

Tool/software:

While testing LLC converter with below specification

Input:- 360V to 410V

Output: - 400V

we are getting the audible noise from LLC converter during No condition. after adding minimum load there no noise from system.

RefDes	Value	Unit
R_BLKupper	14.97	MΩ
R_BLKlower	124	kΩ
R_BWupper
R_BWlower	6.6	KΩ
C_ISNS	150	pF
R_ISNS	42	Ω
C_VCRupper	22	pF
C_VCRlower	2700	pF
Lr	11	uH
Lm	48	uH
Cr	0.054	uF
C_SS	470	nF
R_LLupper	820.00	KΩ
R_LLlower	750.00	KΩ

Please check attached values, suggest which area getting impacted. to eliminate the noise which component needs change.

Thanks & Regards

Eswara rao

3 months ago

0 Sougata Nayak 3 months ago

TI__Intellectual 1270 points

Hi,

In burst mode, controller will make noise as the switching frequency comes under audible range. If you dont want to get audible noise, you may have to disable burst mode.

Regards,

Sougata

0 Eswara rao Gottapu 3 months ago in reply to Sougata Nayak

Prodigy 30 points

Please Suggest changes for burst mode disable, By considering above values only.

0 Sougata Nayak 3 months ago in reply to Eswara rao Gottapu

TI__Intellectual 1270 points

Hi,

You can change Bias winding resistors RBWlower and RBWupper with option no 7 and can use design calculator for computing the same.

Regards,

Sougata

0 Eswara rao Gottapu 3 months ago in reply to Sougata Nayak

Prodigy 30 points

Okay, please confirm how controller will dissipate the energy during No load condition if operates same frequency. what is control method during no load??

0 Sougata Nayak 3 months ago in reply to Eswara rao Gottapu

TI__Intellectual 1270 points

At no load condition, if burst mode is disabled, current will be circulating within the converter itself and it will cause reduction in no load efficiency.

0 Eswara rao Gottapu 3 months ago in reply to Sougata Nayak

Prodigy 30 points

Okay, can you please tell me how current will circulate the within the converter? By changing PWM frequency or Duty?

0 Sougata Nayak 3 months ago in reply to Eswara rao Gottapu

TI__Intellectual 1270 points

Hi,

Please refer page No-20 of below document for analysis.

https://www.ti.com/lit/an/sluaaj7/sluaaj7.pdf?ts=1750912563015&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUCC256404

Regards,

Sougata

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UCC256403: Audible noise from system during no load