Powertrain and Electrification Analog DriversのトピックRe: tl431 regulator resistor

tl431 regulator resistor

Justin_just — Fri, 31 Oct 2025 09:07:32 GMT

Hello team,

i have some doubts and want some clarification regarding TEA1733T ic.

tea1733t ic datasheet:
https://www.nxp.com/docs/en/data-sheet/TEA1733T.pdf

Application notes:

https://www.nxp.com/docs/en/application-note/AN10868.pdf

Fig:1 -This is the reference schematic diagram of TEA1733T IC.

1- My first question is if i want 24v 3 amp as an outpt then what is the value of these resistor R23 and R24 (how these resistors are to be selected),what about R25 and C17?

2- My second question is what is the switching voltage of the MOSFET that fed to the transformer primary side where gate voltage is 10-12V and switching frequency is 66khz?

Thank you.

Re: tl431 regulator resistor

TomasVaverka — Fri, 31 Oct 2025 10:51:01 GMT

Hello Justin,

For a 24V/3A output, the feedback divider (R23 and R24) sets the TL431 reference at 2.5V. The ratio is:

So if R24 = 5.1 kΩ, R23 ≈ 43 kΩ.

R25 and C17 form part of the compensation network for loop stability. Typical values are R25 = 1 kΩ–10 kΩ and C17 = 100 nF–470 nF, tuned per AN10868.

The MOSFET switches the rectified DC bus voltage, which is about 160 V for 115 VAC input or 325 V for 230 VAC input. Gate drive is 10–12 V and the switching frequency is around 66 kHz.

BRs, Tomas

Re: tl431 regulator resistor

Justin_just — Fri, 31 Oct 2025 13:32:59 GMT

Thank you @TomasVaverka for your answer .

Re: tl431 regulator resistor

Justin_just — Mon, 03 Nov 2025 11:46:44 GMT

Hello @TomasVaverka I have some doubts ,can you please explain?

1- What is the purpose of (MBR20100) this D9 and D10 diode ?

2- How OPTIMER and ISENSE pin works internally ?

Application notes:

https://www.nxp.com/docs/en/application-note/AN10868.pdf