LM337TG Detailed explanation of pin function specifications and circuit principle instructions

LM337TG Detailed explanation of pin function specifications and circuit principle instructions

The LM337TG is an adjustable voltage regulator produced by ON Semiconductor. It is a three-terminal adjustable voltage regulator used in power supply circuits, providing a negative voltage output. This part is commonly used for applications where a precise negative output voltage is required. The "TG" suffix typically refers to the TO-220 package type.

Pin Function Specifications and Circuit Principle

The LM337TG belongs to the TO-220 package, which is a through-hole type of package. This package has 3 pins. Below is the detailed description of each pin's function:

Pinout Description (TO-220 Package) Pin Number Pin Name Pin Function Description Pin 1 Adjust This pin is used to adjust the output voltage. It connects to a voltage divider or potentiometer to set the desired negative output voltage. The voltage adjustment is determined by the ratio of two resistors between this pin, the output pin, and ground. Pin 2 Output This is the output pin, providing the regulated negative voltage. It is typically connected to the load in the circuit. Pin 3 Input This is the input pin where the unregulated negative voltage is supplied. A filter capacitor is often used here to stabilize the input voltage.

Detailed Pin Function Explanation:

Adjust Pin (Pin 1): The adjust pin is used to set the output voltage of the LM337TG. By connecting a resistor between the output pin (Pin 2) and adjust pin (Pin 1) and another resistor between the adjust pin (Pin 1) and ground, the output voltage can be adjusted within a given range. The output voltage

is calculated based on the formula:

[ V{OUT} = V{REF} \left( 1 + \frac{R1}{R2} \right) + I_{ADJ} R1 ] Where: (V_{REF}) is the reference voltage (approximately 1.25V), (R1) is the resistor connected between the output pin and the adjust pin, (R2) is the resistor between the adjust pin and ground, (I_{ADJ}) is the small current flowing into the adjust pin (typically small enough to be ignored). Output Pin (Pin 2): The output pin provides the negative regulated voltage, determined by the adjustment of the adjust pin. The LM337TG's voltage regulation ensures that the voltage at this pin remains stable even with varying input voltages, as long as they stay within specified limits. Input Pin (Pin 3): The input pin is where the unregulated negative voltage is fed into the LM337TG. This pin must always have a more negative voltage than the output pin to function correctly.

Frequently Asked Questions (FAQ) about LM337TG:

Q: What is the LM337TG used for? A: The LM337TG is an adjustable negative voltage regulator used in various power supply applications to provide a stable negative voltage output. Q: How do I set the output voltage of the LM337TG? A: The output voltage can be set by adjusting the resistor values between the Adjust pin (Pin 1) and the Output pin (Pin 2) and between the Adjust pin and Ground. Q: What is the maximum output current of the LM337TG? A: The LM337TG can supply up to 1.5A of current, depending on the heat sink and thermal conditions. Q: Can the LM337TG be used for positive voltage regulation? A: No, the LM337TG is specifically designed for negative voltage regulation. For positive voltage regulation, you would use the LM317 or other positive regulators. Q: What is the typical reference voltage for the LM337TG? A: The typical reference voltage is 1.25V between the Output and Adjust pins (Pins 2 and 1). Q: How should I calculate the output voltage? A: The output voltage is calculated using the formula (V{OUT} = V{REF} \left( 1 + \frac{R1}{R2} \right) + I_{ADJ} R1), where R1 and R2 are external resistors. Q: Can the LM337TG regulate a voltage above or below the reference voltage? A: Yes, by using appropriate resistor values, the LM337TG can regulate the output voltage to be either higher or lower than the reference voltage of 1.25V. Q: What is the typical dropout voltage for the LM337TG? A: The typical dropout voltage for the LM337TG is about 3V, meaning the input voltage needs to be at least 3V more negative than the output voltage for proper regulation. Q: Can I use the LM337TG without a heatsink? A: It depends on the power dissipation. If the power dissipation is high (e.g., large difference between input and output voltage), a heatsink is recommended to prevent overheating. Q: What is the thermal resistance of the LM337TG? A: The thermal resistance for the LM337TG is typically 4°C/W when used with a heatsink. Q: Can I use the LM337TG in a buck converter circuit? A: The LM337TG is not designed for switching regulators like buck converters. It is a linear voltage regulator and is suitable for low to moderate current applications. Q: What capacitors should I use with the LM337TG? A: It is recommended to use a 0.1µF ceramic capacitor at the input pin and a 1µF to 10µF electrolytic capacitor at the output pin for stability. Q: What is the output voltage range of the LM337TG? A: The LM337TG can provide an output voltage from -1.25V to -37V, depending on the resistors used for adjustment. Q: Can the LM337TG be used in a battery-powered circuit? A: Yes, as long as the input voltage is sufficiently negative compared to the output voltage, and the current demand is within the regulator's capabilities. Q: What are the limitations of the LM337TG? A: The LM337TG has a limited output voltage range and is inefficient for large voltage drops due to its linear nature, which can lead to significant heat generation. Q: What should I do if the LM337TG is overheating? A: If the LM337TG is overheating, check the power dissipation and consider using a heatsink or improving airflow around the regulator. Q: Is the LM337TG a suitable replacement for the LM317? A: No, the LM317 is a positive voltage regulator, while the LM337TG is a negative voltage regulator. They cannot directly replace each other. Q: Can I use the LM337TG to power a motor? A: The LM337TG is not ideal for motor applications due to its low efficiency and potential overheating. A dedicated motor driver IC is recommended. Q: What is the maximum input voltage for the LM337TG? A: The maximum input voltage is typically -40V, but it is essential to check the datasheet for specific limits. Q: How do I protect the LM337TG from overvoltage? A: To protect the LM337TG, you can use a zener diode or a clamp circuit to limit the input voltage to a safe range.

Conclusion

The LM337TG is a versatile adjustable negative voltage regulator with a TO-220 package and three pins. It provides a stable negative voltage output and is widely used in power supply applications. Proper calculation and adjustment of resistor values between the pins allow for custom output voltage configurations.