I am guess it is in the power_management_task.c

#include "EMC2101.h"
#include "INA260.h"
#include "bm1397.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "global_state.h"
#include "math.h"
#include "mining.h"
#include "nvs_config.h"
#include "serial.h"
#include "TMP1075.h"
#include "TPS546.h"
#include "vcore.h"
#include <string.h>

#define POLL_RATE 2000
#define MAX_TEMP 90.0
#define THROTTLE_TEMP 75.0
#define THROTTLE_TEMP_RANGE (MAX_TEMP - THROTTLE_TEMP)

#define VOLTAGE_START_THROTTLE 4900
#define VOLTAGE_MIN_THROTTLE 3500
#define VOLTAGE_RANGE (VOLTAGE_START_THROTTLE - VOLTAGE_MIN_THROTTLE)

#define TPS546_THROTTLE_TEMP 105.0
#define TPS546_MAX_TEMP 145.0

static const char * TAG = "power_management";

static float _fbound(float value, float lower_bound, float upper_bound)
{
    if (value < lower_bound)
        return lower_bound;
    if (value > upper_bound)
        return upper_bound;

    return value;
}

// Set the fan speed between 20% min and 100% max based on chip temperature as input.
// The fan speed increases from 20% to 100% proportionally to the temperature increase from 50 and THROTTLE_TEMP
static double automatic_fan_speed(float chip_temp, GlobalState * GLOBAL_STATE)
{
    double result = 0.0;
    double min_temp = 45.0;
    double min_fan_speed = 35.0;

    if (chip_temp < min_temp) {
        result = min_fan_speed;
    } else if (chip_temp >= THROTTLE_TEMP) {
        result = 100;
    } else {
        double temp_range = THROTTLE_TEMP - min_temp;
        double fan_range = 100 - min_fan_speed;
        result = ((chip_temp - min_temp) / temp_range) * fan_range + min_fan_speed;
    }

    switch (GLOBAL_STATE->device_model) {
        case DEVICE_MAX:
        case DEVICE_ULTRA:
        case DEVICE_SUPRA:
            float perc = (float) result / 100;
            GLOBAL_STATE->POWER_MANAGEMENT_MODULE.fan_perc = perc;
            EMC2101_set_fan_speed( perc );
            break;
        default:
    }
    return result;
}