Current Limit Of Linear Power Regulator Based On LM350
Current Limit of Linear Power Regulator Based on LM350: Understanding the Limitations
Introduction
When it comes to designing a linear power supply (PSU), one of the key components is the linear regulator. The LM350 is a popular choice among electronics enthusiasts and professionals due to its high current capability and low dropout voltage. However, as with any linear regulator, there are limitations to its performance, particularly when it comes to current limiting. In this article, we will delve into the current limit of linear power regulators based on the LM350 and explore the reasons behind its non-linear behavior.
Background on Linear Regulators
Linear regulators are a type of voltage regulator that use a linear control mechanism to regulate the output voltage. They are commonly used in power supplies, audio equipment, and other applications where a stable output voltage is required. The LM350 is a popular linear regulator that can handle high currents and has a low dropout voltage, making it suitable for a wide range of applications.
Current Limiting in Linear Regulators
Current limiting is a critical feature in linear regulators, as it prevents the regulator from delivering more current than it can handle. This is particularly important in applications where the load current may vary, such as in power supplies or audio equipment. The LM350 has a built-in current limiting feature that is designed to prevent the regulator from overheating or damaging the load.
The Problem with Non-Linear Current Limiting
However, as you may have noticed, the current limit of the LM350 is not always linear. When adjusting the R5 potentiometer, the circuit seems to jump between two limiting points, rather than smoothly increasing or decreasing the current limit. This non-linear behavior can be frustrating, especially when trying to fine-tune the current limit for a specific application.
Understanding the Causes of Non-Linear Current Limiting
So, what causes the non-linear current limiting behavior in the LM350? There are several factors that contribute to this phenomenon:
- Internal Current Limiting Circuitry: The LM350 has an internal current limiting circuit that is designed to prevent the regulator from delivering more current than it can handle. This circuitry is based on a simple comparator circuit that compares the output current to a reference voltage. When the output current exceeds the reference voltage, the comparator triggers a current limiting action.
- R5 Potentiometer: The R5 potentiometer is used to adjust the current limit of the LM350. However, the potentiometer is not a linear device, and its resistance changes in a non-linear manner as the wiper moves. This non-linearity can cause the current limit to jump between two limiting points, rather than smoothly increasing or decreasing.
- Load Current Variations: The load current can vary significantly depending on the application. For example, in a power supply, the load current may increase or decrease as the load is connected or disconnected. This variation in load current can cause the current limit to jump between two limiting points.
Mitigating Non-Linear Current Limiting
So, how can you mitigate the non-linear current limiting behavior in the LM350? Here are a few suggestions:
- Use a Linear Potentiometer: Instead of using a non-linear potentiometer, consider using a linear potentiometer. This will help to smooth out the current limit and prevent it from jumping between two limiting points.
- Add a Current Limiting Circuit: Consider adding a current limiting circuit to the LM350. This can be a simple circuit that uses a comparator and a current limiting resistor to prevent the regulator from delivering more current than it can handle.
- Use a Different Linear Regulator: If the non-linear current limiting behavior is a major concern, consider using a different linear regulator that has a more linear current limiting characteristic.
Conclusion
In conclusion, the current limit of linear power regulators based on the LM350 is not always linear. This non-linear behavior can be caused by a combination of factors, including internal current limiting circuitry, non-linear potentiometer behavior, and load current variations. By understanding the causes of non-linear current limiting and using mitigating strategies, you can help to smooth out the current limit and prevent it from jumping between two limiting points.
References
- National Semiconductor Corporation. (1999). LM350 Linear Regulator Datasheet.
- Texas Instruments Incorporated. (2019). TL431 Linear Regulator Datasheet.
Additional Resources
- Linear Regulator Tutorial by Analog Devices
- Current Limiting in Linear Regulators by Linear Technology
- Power Supply Design Tutorial by Texas Instruments
Related Articles
- Understanding Linear Regulators
- Current Limiting in Power Supplies
- Power Supply Design Considerations
Frequently Asked Questions: Current Limit of Linear Power Regulator Based on LM350
Introduction
In our previous article, we discussed the current limit of linear power regulators based on the LM350 and explored the reasons behind its non-linear behavior. In this article, we will answer some of the most frequently asked questions related to the current limit of linear power regulators based on the LM350.
Q: What is the current limit of the LM350?
A: The current limit of the LM350 is typically around 1.5A to 3A, depending on the input voltage and the load current. However, the current limit can vary depending on the specific application and the values of the external components.
Q: Why does the current limit of the LM350 jump between two limiting points?
A: The current limit of the LM350 jumps between two limiting points due to the non-linear behavior of the internal current limiting circuitry and the R5 potentiometer. The internal current limiting circuitry is based on a simple comparator circuit that compares the output current to a reference voltage. When the output current exceeds the reference voltage, the comparator triggers a current limiting action. However, the R5 potentiometer is not a linear device, and its resistance changes in a non-linear manner as the wiper moves. This non-linearity can cause the current limit to jump between two limiting points.
Q: How can I adjust the current limit of the LM350?
A: The current limit of the LM350 can be adjusted using the R5 potentiometer. However, it's essential to note that the potentiometer is not a linear device, and its resistance changes in a non-linear manner as the wiper moves. To adjust the current limit, you can use a linear potentiometer or add a current limiting circuit to the LM350.
Q: What are the limitations of the LM350 current limiting circuit?
A: The LM350 current limiting circuit has several limitations, including:
- Non-linear behavior: The current limiting circuit is based on a simple comparator circuit that compares the output current to a reference voltage. However, the comparator is not a linear device, and its behavior can be affected by various factors, including temperature and input voltage.
- Limited current range: The current limiting circuit is designed to limit the output current to a specific range, typically around 1.5A to 3A. However, the current limit can vary depending on the specific application and the values of the external components.
- Sensitivity to load current variations: The current limiting circuit is sensitive to load current variations, which can cause the current limit to jump between two limiting points.
Q: Can I use a different linear regulator with a more linear current limiting characteristic?
A: Yes, you can use a different linear regulator with a more linear current limiting characteristic. Some popular alternatives to the LM350 include the TL431 and the ADP1710. These regulators have more advanced current limiting circuits that can provide a more linear current limiting characteristic.
Q: What are the design considerations for a linear power supply with a current limiting circuit?
A: When designing a linear power supply with a current limiting circuit, there are several design considerations to keep in mind, including:
- Current limiting range: The current limiting range should be set to a value that is higher than the maximum load current.
- Current limiting accuracy: The current limiting accuracy should be set to a value that is within 10% of the desired current limit.
- Load current variations: The load current variations should be taken into account when designing the current limiting circuit.
- Temperature and input voltage effects: The temperature and input voltage effects should be taken into account when designing the current limiting circuit.
Conclusion
In conclusion, the current limit of linear power regulators based on the LM350 is not always linear, and it can be affected by various factors, including internal current limiting circuitry, non-linear potentiometer behavior, and load current variations. By understanding the causes of non-linear current limiting and using mitigating strategies, you can help to smooth out the current limit and prevent it from jumping between two limiting points.
References
- National Semiconductor Corporation. (1999). LM350 Linear Regulator Datasheet.
- Texas Instruments Incorporated. (2019). TL431 Linear Regulator Datasheet.
- Analog Devices. (2020). ADP1710 Linear Regulator Datasheet.
Additional Resources
- Linear Regulator Tutorial by Analog Devices
- Current Limiting in Linear Regulators by Linear Technology
- Power Supply Design Tutorial by Texas Instruments
Related Articles
- Understanding Linear Regulators
- Current Limiting in Power Supplies
- Power Supply Design Considerations