How to Use LD33 Low-Dropout Voltage Regulator: Examples, Pinouts, and Specs

The LD33 is a low-dropout (LDO) voltage regulator capable of providing a fixed output voltage of 3.3V with a maximum output current of up to 800mA. This component is ideal for applications requiring a stable 3.3V supply from input voltages that are very close to the output voltage, such as battery-powered devices, microcontroller circuits, and portable electronics.

• Power supply for 3.3V logic ICs and microcontrollers
• Battery-powered devices requiring a stable 3.3V
• Peripheral power supply for microprocessor systems
• Portable electronics and wearable devices

• Output Voltage (Vout): 3.3V
• Input Voltage (Vin): 4.5V to 7V (recommended operating range)
• Dropout Voltage: Typically 1V at 800mA load
• Output Current (Iout): Up to 800mA
• Quiescent Current: Typically 5µA
• Temperature Range: -40°C to +125°C

1. Connect the input voltage (4.5V to 7V) to the IN pin of the LD33.
2. Connect the GND pin to the system ground.
3. The OUT pin will provide a regulated 3.3V output. Connect this to the circuit requiring a 3.3V supply.
4. Optionally, add a capacitor (typically 10µF) between the IN pin and GND close to the regulator to stabilize the input supply.
5. Similarly, add a capacitor (typically 10µF) between the OUT pin and GND to filter any output noise.

• Ensure that the input voltage is within the specified range to prevent damage to the LD33.
• Do not exceed the maximum output current of 800mA.
• Use capacitors on the input and output as recommended to minimize voltage fluctuations and noise.
• Provide adequate heat sinking if the regulator is expected to dissipate significant power due to high load current or a large voltage drop from input to output.

• Output voltage is lower than 3.3V: Check if the input voltage is within the recommended range and if the load current is not exceeding 800mA.
• Regulator is overheating: Ensure that the power dissipation is within the limits and improve heat sinking if necessary.
• Output voltage is unstable: Verify the presence and correct value of the input and output capacitors.

• If the output voltage is incorrect, recheck the input voltage and load conditions.
• For overheating issues, reduce the load current or improve heat dissipation.
• For voltage instability, ensure that the recommended capacitors are used and are placed close to the regulator pins.

Q: Can I use the LD33 without capacitors? A: While the LD33 may work without capacitors, it is strongly recommended to use them for stability and noise reduction.

Q: What is the maximum input voltage for the LD33? A: The absolute maximum input voltage is typically around 15V, but for safe and reliable operation, keep the input voltage within the recommended range of 4.5V to 7V.

Q: How can I increase the output current capability? A: The LD33 is rated for a maximum of 800mA. If you need more current, consider using a regulator with a higher current rating or parallel multiple LD33 regulators with proper current sharing measures.

Q: Is the LD33 regulator suitable for battery-powered applications? A: Yes, the LD33's low quiescent current makes it suitable for battery-powered applications where power efficiency is crucial.

// No specific code is required for using the LD33 with an Arduino UNO.
// The following example demonstrates how to power an Arduino UNO with the LD33.

// Connect the LD33 as follows:
// LD33 IN pin -> External power supply (4.5V to 7V)
// LD33 GND pin -> External power supply ground and Arduino GND pin
// LD33 OUT pin -> Arduino 3.3V pin

void setup() {
  // Initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  // Turn the LED on (HIGH is the voltage level)
  digitalWrite(LED_BUILTIN, HIGH);
  // Wait for a second
  delay(1000);
  // Turn the LED off by making the voltage LOW
  digitalWrite(LED_BUILTIN, LOW);
   // Wait for a second
  delay(1000);
}

Remember that the Arduino UNO's 3.3V pin is an output, not an input. To power the board with the LD33, connect the LD33's output to a breadboard rail and power the 3.3V components from there, not directly to the Arduino's 3.3V pin.