Comprehensive Understanding of the 78M05 Chip
14 March 2024
Ⅰ. Development history of linear voltage regulators
Ⅳ. External components of 78M05
Ⅴ. Technical key points of 78M05
Ⅵ. Internal circuit diagram of 78M05
Ⅶ. Judgment of the quality of 78M05
Ⅷ. How to optimize the static power consumption of 78M05?
The 78M05 is a linear voltage regulator chip that is mainly used for DC power stabilization and filtering. Its internal circuit protection function is integrated so that it can ensure the safety and stable operation of the equipment. In this article, we will help you better understand the features and advantages of this device through a detailed introduction of the 78M05's pin diagram and function, external components, technical points, and internal circuit diagrams, which will provide a reference for your subsequent circuit design and use.
A linear voltage regulator is a device used to stabilize the output voltage in a circuit. Its development can be traced back to the 1960s. At that time, resistor voltage division was often used in circuits of electronic equipment to achieve voltage stability, but this method had problems such as low efficiency and high power consumption. In order to solve these problems, researchers began to look for more efficient and stable voltage stabilizing devices.
In 1964, National Semiconductor produced the first linear regulator device, the LM100. This voltage stabilizing device uses the structure of a current source and a differential amplifier to provide a stable output voltage and also has high anti-interference capabilities. With the development of technology, linear voltage regulator devices have been gradually improved. In the early 1970s, National Semiconductor introduced a new linear voltage regulator device, the LM309, which used the structure of a current source and a differential amplifier to provide higher output current and lower output voltage.
However, traditional linear voltage regulator devices have some shortcomings, such as low efficiency and large heat dissipation. In order to solve these problems, researchers began to develop new linear voltage regulator devices. In the 1980s, National Semiconductor introduced a new linear voltage regulator called the 78M05. 78M05 is an improvement based on the structure of the previous generation voltage regulator device LM309. It uses a bipolar transistor power amplifier structure with higher efficiency and lower heat dissipation. The "78" in the name of 78M05 means that it is the 78th linear voltage regulator device produced by National Semiconductor, and the "M05" means that it is a voltage regulator device with an output voltage of 5V. In addition to 5V output voltage, there are other models with different output voltages, such as 78M03 (3V output voltage), 78M12 (12V output voltage), etc.
Over time, linear regulator devices have been further improved and developed. Now, there are more new linear voltage regulator devices on the market, which have higher efficiency, lower heat dissipation, smaller size and other characteristics.
78M05 is a three-port current positive fixed voltage regulator, which is one of the 78 series three-terminal voltage regulators. The regulator's maximum output current is 500mA, its input bias current is 3.2mA, and its maximum input voltage is limited to 35V. In addition to stable output voltage and high output current capabilities, the 78M05 also has a number of notable features. For example, it has a built-in overheating protection function that automatically reduces the output current once the temperature exceeds the safe range to ensure that the chip is not damaged. In addition, it also has overload protection and short-circuit protection functions. When the circuit is overloaded or short-circuited, it can automatically cut off the output current to prevent circuit damage. Due to these stability and protection functions, 78M05 has been widely used in a variety of equipment, such as power supply in car audio, LED lighting and other fields, as well as in power management circuits of communication equipment and electronic equipment.
Alternatives and equivalents:
• LM340
• LM340A
The 78M05 has a total of three pins, namely input pin (Vin), ground pin (GND) and output pin (Vout). The pin layout is as follows:
1. Input pin (Vin): used to receive input voltage, usually connected to the positive pole of the power supply.
2. Ground pin (GND): used for grounding, connected to the negative pole of the power supply.
3. Output pin (Vout): used to output a stable voltage.
The main external components of 78M05 include:
1. Output filter capacitor: Its main function is to suppress self-oscillation. However, its capacity should be smaller than the input filter capacitor, and a capacity of tens of microfarads (μF) to hundreds of microfarads (μF) is usually selected. When connecting, the positive pole of the filter capacitor should be connected to the output terminal of the 78M05, and the negative pole should be connected to the power ground.
2. Input filter capacitor: Its positive pole should be connected to the input terminal of 78M05, and its negative pole should be connected to the power ground. This input filter capacitor is necessary when the input is a rectified unidirectional pulsating voltage. Its capacity is related to the output current. It is generally recommended to choose a capacity above 1000μF. However, if the input is already a DC voltage and an external protection diode is connected, then this input filter capacitor can be omitted.
3. Protection diode: Its positive pole should be connected to the output terminal of 78M05, and its negative pole should be connected to the input terminal of 78M05. Its main function is to prevent the input terminal voltage from being significantly lower than the output terminal when the input terminal of the 78M05 is powered off, thereby protecting the circuit. If the input filter capacitor has been connected to the circuit, this protection diode can be omitted.
1. Temperature protection
The voltage regulator has built-in temperature protection. When the operating temperature exceeds the set threshold, it automatically shuts down the protection circuit. This function can effectively avoid damage or dangerous situations caused by overheating of the equipment.
2. Short circuit protection
78M05 has a short-circuit protection function. When a short-circuit occurs in the load, the voltage regulator can automatically cut off the current to prevent the chip and other components from being damaged due to short-circuit. This function can effectively protect the security of the device and improve the stability of the device.
3. Output transistor safe operating area (SOA) protection
In order to protect the output transistor from damage by excessive current, 78M05 adopts SOA protection function to ensure that the output current operates within a safe range. This function can effectively avoid damage to the output transistor and improve the stability of the device.
4. Thermal overload protection
The 78M05 also has built-in thermal overload protection. When the chip temperature is too high, it will automatically detect and shut down the protection circuit to prevent the chip and other components from being damaged. This feature can effectively extend the life of the voltage regulator and improve the reliability of the device.
5. Wide input voltage range
The input voltage range of 78M05 is 7V to 30V. This feature enables it to adapt to a variety of input voltage requirements in different application scenarios, thus showing application value in power management circuits. Whether in low-voltage equipment or high-voltage equipment, 78M05 can work stably and exert its excellent performance.
A typical integrated linear regulator usually only requires VIN (input voltage), VOUT (output voltage), FB (feedback), and optionally GND (ground) pins. As a typical 3-pin linear regulator, the 78M05 has a particularly simple design, requiring only one input capacitor and one output capacitor to set the output voltage. Therefore, almost any electrical engineer can easily design power supplies using these simple linear regulators.
We can judge whether 78M05 is good or bad from the following aspects:
1. Voltage withstand test: We can perform a voltage withstand test to ensure that the 78M05 is able to withstand stable operation within the rated operating voltage range and that there is no leakage or breakdown.
2. Source reliability: We usually choose 78M05 from reliable manufacturers and suppliers with good reputation, which can ensure the quality control of raw materials and manufacturing.
3. Specification compliance: We need to verify that the specifications of the 78M05 meet the standard requirements, such as whether the output voltage is +5V and the input voltage range is between 7V and 25V. A non-compliant chip may result in unstable output or not work properly.
4. Temperature and load test: By conducting temperature and load tests on the 78M05, we were able to evaluate its stability and reliability under different operating conditions. A high-quality 78M05 should be able to work continuously and efficiently under rated operating conditions.
We can optimize the static power consumption of 78M05 in the following ways.
First, optimize the circuit design. When designing the power circuit, we try to reduce unnecessary components and lines to reduce the power consumption of the entire circuit. In addition, through reasonable circuit design, we can reduce the voltage drop and current loss on the power line, thereby reducing power consumption.
Secondly, choose alternative products with low power consumption. There may be some similar products on the market with lower static power consumption, and we can consider replacing the 78M05 to further reduce power consumption.
Third, use low-power operating modes. If the 78M05 supports low-power operation mode, then we can enable this mode to reduce power consumption when high output current is not required.
Fourth, perform thermal design. Although the static power consumption itself is low, the 78M05's efficiency will be affected in a high temperature environment, which may lead to an increase in power consumption. Therefore, a proper thermal design can help keep the 78M05 at a lower operating temperature, thus maintaining lower power consumption.
Fifth, select the proper input voltage. 78M05 requires an input voltage of at least 7V for proper operation. While ensuring a stable output voltage, minimizing the input voltage can effectively reduce power consumption. Because the higher the input voltage, the higher the current flowing through the regulator, the static power consumption increases accordingly.
Frequently Asked Questions
1. Where are regulators used?
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant.
2. What is the function of 78m05?
The LM78M05-MIL three-pin positive voltage regulator employs built-in current limiting, thermal shutdown, and safe-operating area protection, which makes them virtually immune to damage from output overloads. With adequate heat sinking, they can deliver in excess of 0.5-A output current.
3. What is LM7805 used for?
LM7805 is one of the most commonly used positive regulator in electronic circuits to lower down the voltage from the higher input voltage and it provides a regulated output of +5V with 2% regulation. This regulator has a 2.5V linear drop-out.
