Arduino battery charger withtwo TL431 voltage detectors.
Fig. 1 Arduino battery charger with two TL431 voltage detectors.

TL431 Battery Charger Voltage Detector Circuits Schematics

by Lewis Loflin

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Fig. 2 Arduino with TL431 voltage detectors control
battery charge current with LM317-MJ2955.
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Opto-isolated constant current source using an LM317 and LM358 current monitor.
Fig. 3
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Fig. 4 Arduino battery charger with opto-isolated
CCS and 2 TL431 voltage comparators.
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Note: Indicator LEDs DP9, DP10, and DP11 not shown.

Fig. 5 A TL431 shunt regulator circuit configured
as a voltage comparator.

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Fig. 6 TL431 over voltage detector with optocoupler output.

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Arduino Code for Above Circuits

/*
  Use pwm to control output current
  for constant current source for battery charger
*/

#define TL431A 4 // HIGH out V = set
#define TL431B 5 // HIGH out V = set
#define pwmOut 6

// 1K resistor to GRD.
#define redLed 11
#define yellowLed 10
#define greenLed 9

#define ccsHigh 255 // 100%
#define ccsMed 144 // 50%
#define ccsLow 45 // 25%
#define ccsOff 0 // 0% or OFF

int temp = 0;

void setup() {

  // High from TL431 Vin > Rset
  pinMode(TL431A, INPUT);  // Rset = 12.6V
  pinMode(TL431B, INPUT);  // Rset = 13.6V

  pinMode(redLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(greenLed, OUTPUT);

  pinMode(pwmOut, OUTPUT); // CCS optocoupler
  Serial.begin(9600);
  Serial.println("Serial OK");
}

void loop() {
  // battery voltage less than 12.6V
  if (digitalRead(TL431A) == 0 && digitalRead(TL431B) == 0) {
    digitalWrite(redLed, HIGH); // high charge rate
    digitalWrite(yellowLed, LOW);
    digitalWrite(greenLed, LOW);
    delay(500);
    temp = ccsHigh;
  }   // 1 Amp

  // battery voltage 12.6V to 13.6V
  if (digitalRead(TL431A) == 1 && digitalRead(TL431B) == 0) {
    digitalWrite(redLed, LOW);
    digitalWrite(yellowLed, HIGH); // medium charge rate
    digitalWrite(greenLed, LOW);
    delay(500);
    temp = ccsMed; // slow charge rate can use ccsLow
  }   // 0.5 Amps

  // battery voltage V > 13.6V
  if (digitalRead(TL431A) == 1 && digitalRead(TL431B) == 1) {
    digitalWrite(redLed, LOW);
    digitalWrite(yellowLed, LOW);
    digitalWrite(greenLed, HIGH); // charged
    delay(500);
    temp = ccsOff; // charged turn off
  }   // 0 Amps

  analogWrite(pwmOut, temp);
  Serial.print("PWM value = ");
  Serial.println(temp);
  delay(5000);  // delay 5 Sec.
}

Using TL431A Li-Ion Battery Charger Tutorials
TL431A Lithium-Ion Cell Charging Circuits
Charging Multi-Cell Lithium-Ion Battery Packs
TL431 Over-Voltage, Under-Voltage Detector Circuits
TL431A Constant Current Source Working Circuits Demo
Power TL431 Constant Current Source Circuits

TL431 Battery Charger Voltage Detector Circuits Schematics

Arduino Code for Above Circuits

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