78L05: How to use, working principle and application areas of thermal shutdown function

By CJ 90

78L05: How to use, working principle and application areas of thermal shutdown function

78L05 is a common linear voltage regulator IC, also known as a positive voltage regulator. It is a component designed based on a fixed positive voltage regulator and is used to provide stable 5V DC power supply. In the 78L05 voltage regulator, the first two numbers like "78" are positive voltage, 05 is the output voltage produced by the IC, like 5V, and the letter "L" between 78 and 05 is low current, like 0.1A. This voltage regulator is used in most electronic projects.

The 78L05 has internal current limiting and thermal shutdown features, making it particularly suitable for overload conditions. When using the 78L05 as an alternative, the output impedance is significantly improved while the bias current is greatly reduced compared to a traditional Zener diode-resistor bank.

Due to the excellent performance and stability of 78L05, it is widely used in various electronic equipment, including computers, electronic instruments, communication equipment and consumer electronics products. In these applications, 78L05 can ensure stable operation of the circuit and provide reliable power support.

Ⅰ.Specification parameters of 78L05

•Number of voltage regulators:1
•Output Configuration:Positive
•Output type:Fixed
•Junction temperature:-22℃ to 125℃
•Power consumption:500mW
•Operating temperature:-20℃ to 85℃
•Storage temperature:-65℃ to 150℃
•Current-Quiescent (Iq):5.5 mA
•Voltage-Input (maximum):30V
•Voltage-Output (min/fixed):5V
•Voltage drop (max):1.7V@40mA
•Protection functions:overcurrent, overtemperature, short circuit

Ⅱ.Pin configuration of 78L05

•Pin1 (output Vo): output voltage regulation +5V
•Pin2 (Gnd): Connect to ground
•Pin3(V+): Unregulated input voltage

Ⅲ.How to use 78L05

1.Wiring: Connect the input power to the 78L05's input pin (usually labeled Vin), and connect the load (such as a circuit or device) to the output pin (usually labeled Vout). At the same time, connect the ground pin to the ground wire.

2.Input voltage: Make sure the input voltage is within the rated input voltage range of 78L05. Generally speaking, its typical input voltage range is 7V to 20V. Exceeding this range may damage the regulator.

3.Capacitance: Generally, in order to improve the stability and performance of the voltage regulator, it is recommended to add appropriate capacitance between the input and output pins. Connect an electrolytic capacitor in parallel between the input pin and ground. The capacitance is usually between 0.33μF and 1μF. Connect a smaller capacitor in parallel between the output pin and ground, usually between 0.1μF and 0.33μF.

4.Output voltage: 78L05 stabilizes the input voltage to 5V output. You can verify that the output is stable around 5V by measuring the voltage at the output pin.

5.Overload protection: Although the 78L05 has a certain overload protection function, exceeding its rated output current should still be avoided. Make sure the load does not exceed the 78L05's maximum output current.

6.Heat dissipation: If the load is large or the ambient temperature is high, an additional heat sink may be needed to cool the voltage regulator chip to ensure that the voltage regulator operates within a safe temperature range.


Ⅳ.Working principle of thermal shutdown function of 78L05

The 78L05 voltage regulator has a thermal shutdown feature to protect the chip from overheating. When the chip temperature exceeds its rated operating temperature range, the thermal shutdown function will automatically trigger, causing the chip to stop working, thereby preventing overheating damage.

Specifically, there is a temperature-sensitive element inside the 78L05. When the temperature exceeds a preset safety threshold, this temperature-sensitive element will change its resistance value or electrical characteristics. This change will be detected by the 78L05's internal control circuit, which will then disconnect the output and stop providing power to the load, thereby preventing damage caused by overheating.

When the temperature inside the 78L05 drops to a safe range, the thermal shutdown function will automatically reset, and the 78L05 will restart working and provide power to the load. This automatic reset feature allows the 78L05 to protect itself in the event of overheating and continue to operate after the temperature returns to normal.

The thermal shutdown function of the 78L05 does not completely prevent overheating, but only protects it. Therefore, in the design of the circuit, other methods such as adding heat sinks and reducing load current should also be considered to avoid overheating. In addition, when the thermal shutdown function of 78L05 starts up frequently, it is necessary to carry out circuit design and load condition detection to avoid long-term overheating and damage to the circuit.

Ⅴ.Correct selection and use of 78L05

1.Understand the parameter specifications: First, you need to understand the basic parameter specifications of the 78L05, including its maximum input voltage, minimum input voltage, maximum output voltage, minimum output voltage, and maximum output current. These parameters will determine whether the 78L05 is suitable for your application.

2.Heat dissipation considerations: Since the 78L05 generates heat during operation, appropriate heat dissipation measures need to be considered. This can be accomplished by adding heat sinks, reducing load current, or improving ventilation.

3.Consider the package type: 78L05 has multiple package types, such as TO-92, SOT-89, SOIC, etc. The appropriate package type needs to be selected based on the circuit board design and application requirements.

4.Working environment temperature: The working temperature range of 78L05 is usually 0°C to +125°C. It is necessary to ensure that the application environment is within this temperature range to ensure the normal operation of 78L05.

5.Consideration of load current: The maximum output current of 78L05 depends on its package type, usually between 100mA and 500mA. It is necessary to ensure that the application load current is within this range to prevent overheating or damage to the device.

6.Input and output voltage considerations: Make sure the input voltage of the 78L05 is always higher than its output voltage to prevent damage to the device. At the same time, we should also pay attention to whether its maximum output voltage and minimum output voltage meet the application requirements.

7.Circuit layout and wiring: When laying out and wiring on the circuit board, the resistance and inductance between the power line and the ground line should be minimized to improve the stability and efficiency of the power supply.

8.Short circuit and overheating protection: Although 78L05 has overheating protection and short circuit protection functions, you should still try to avoid short circuit and overheating situations. If this occurs, disconnect the power supply immediately and check the circuit.


VI.Application fields of 78L05

1.Household appliances: including televisions, audio systems, microwave ovens, etc., will use 78L05. The main function of 78L05 is to provide stable 5V power supply for key components on the circuit board. In household appliances, the application of 78L05 is mainly reflected in the following aspects:

•Control circuit power supply: In some household appliances, the control circuit requires a stable power supply to ensure its normal operation. 78L05 can provide the required 5V power supply for these control circuits to ensure the normal operation of household appliances.

•Standby power supply: For many household appliances, it is necessary to provide stable power supply to some key components even in standby mode. The 78L05 can provide the required 5V power to these components to ensure that they can operate normally in standby mode.

•Digital logic circuit power supply: In household appliances, digital logic circuits are widely used in various control and signal processing processes. 78L05 can provide a stable 5V power supply to these digital logic circuits, ensuring that they can perform various tasks accurately and reliably.

2.Medical equipment: 78L05 is used in various medical monitoring equipment, medical sensors, etc. As a fixed-voltage three-terminal integrated voltage regulator, 78L05’s excellent internal current limit and thermal shutdown characteristics make it widely used in medical equipment. widely used in. The stable output voltage of 78L05 ensures that the sensor can accurately measure and transmit physiological parameters, such as temperature, pressure, flow, etc.

3.Industrial automation: including factory equipment, sensors, robots, etc., 78L05 is often used to provide stable power supply.

4.Automotive electronics: In automotive electronic systems, 78L05 is used to provide stable power to various electronic control units, such as engine control units, instrument panels, vehicle entertainment systems, etc.

•Engine control unit (ECU): ECU is the core electronic component of the car and is responsible for controlling various parameters of the engine, such as fuel injection, ignition timing, etc. 78L05 provides a stable 5V power supply to the ECU, ensuring that the engine can be accurately controlled according to different driving conditions and needs.

•Instrument panel and display system: The automobile's instrument panel and various display systems require stable power supply to ensure accurate displays and readings. 78L05 provides reliable 5V power supply for these systems, allowing the driver to understand the vehicle's status and driving information at any time.

•In-vehicle entertainment systems: Audio, navigation systems and other in-vehicle entertainment devices in modern cars require stable power to ensure clear sound quality, accurate navigation and good user experience. The 78L05 provides 5V power to these devices, ensuring they can operate stably in a variety of driving conditions.

5.Electronic equipment: 78L05 is often used to provide stable 5V power supply to various digital circuits, analog circuits and power management circuits, such as microcontrollers, logic circuits, sensors, operational amplifiers, etc.

6.Electronic instruments: 78L05 can be used in various electronic instruments, such as measuring equipment, laboratory equipment and testing instruments. Among these devices, 78L05 provides a stable 5V power supply to ensure the normal operation of circuit components.

7.Power adapter: 78L05 can be used to design small power adapters to provide stable power for devices that require 5V input.

8.Communication equipment: Wireless communication equipment, network equipment and telephone systems all require stable power to ensure their normal operation. The 78L05 can provide the required 5V stable power supply for these devices.

9.Logic circuit power supply: Many digital logic circuits (such as TTL, CMOS) require 5V stable power supply, and 78L05 can provide stable operating voltage for these circuits.

10.Computer hardware: Computers and their related hardware often require reliable voltage regulators to provide stable power. The 78L05 can be used to power computer motherboards, graphics cards, hard drives, and other peripheral devices.

11.Battery-powered applications: In battery-powered applications, 78L05 can convert the unstable output voltage of the battery into a stable 5V power supply to supply electronic equipment and circuits.

12.Microcontroller and sensor power supply: Many microcontrollers (such as Arduino, PIC, AVR, etc.) and sensors (such as temperature sensors, humidity sensors, light sensors, etc.) require 5V stable power supply, and 78L05 can meet these needs.


Ⅶ.Methods to detect damage to 78L05

1.Measure the input voltage: First, check whether the input voltage is within the rated range. If the input voltage exceeds the rated input voltage range of the 78L05, the regulator may be damaged.

2.Measure the output voltage: Use a multimeter or oscilloscope to measure the output voltage. You should get a stable output voltage close to 5V. If the output voltage is far away from 5V, or fluctuates greatly, it may mean that the 78L05 is damaged.

3.Replace with a new voltage regulator: If the above inspection still cannot determine whether the 78L05 is damaged, you can try to replace it with a new voltage regulator and test the input and output voltages again. If the new regulator is working properly, the original 78L05 may be damaged.

4.Check the thermal condition: Touch the 78L05 chip to check whether its temperature is abnormally high. If the chip overheats, it may indicate that the regulator is damaged or has an overload condition.

5.Check the surrounding circuits: Sometimes voltage regulator damage may be caused by excessive load, short circuit or other circuit problems. Therefore, it is also important to check whether the surrounding circuit connections are correct and to rule out other circuit problems.

(VI=10V,Io=40mA,0<Tj<125°C,C1=0.33μF,Co=0.1μF,unless otherwise specified)


Frequently Asked Questions

1.What is the function of 78L05?
The function of 78L05 is to take an input voltage (typically higher than 5 volts) and regulate it down to a stable 5-volt output.

2.What is the dropout voltage of 78L05?
The dropout voltage of 78L05 is typically around 2 volts.

3.What is the thermal shutdown feature of 78L05?
The thermal shutdown feature of 78L05 protects the device from over-temperature conditions by shutting down the regulator if the temperature exceeds a certain threshold.

4.How is 78L05 typically connected in a circuit?
78L05 is typically connected by connecting the input voltage to the Vin pin, the load to the Vout pin, and grounding the GND pin.