A three-terminal regulator helps keep circuits safe and working well. You use a three-terminal regulator to give a steady voltage. This stops devices from breaking. If voltage changes too much, bad things can happen. You might see lights flicker, get hot, or sensors stop working right.
LEDs can flicker or get dim.
Parts can wear out faster from heat.
Power supplies can get too hot and waste energy.
Sensors and control units might send wrong signals.
Circuits can break more often and not work as well.
You can trust a regulator for easy design and steady work. Learning how a three-terminal regulator works helps you pick the best one for your projects.
Key Takeaways
A three-terminal regulator keeps voltage steady. This helps protect devices from harm. It also makes sure things work well.
It has three pins: input, output, and ground or adjust. These pins work together to control voltage. They help keep voltage stable.
Safety features are built in. These include overcurrent and thermal protection. They stop damage and help devices last longer.
There are fixed and adjustable types. You can pick steady or custom voltages. This is good for different projects.
Three-terminal regulators are simple to use. They need only a few extra parts. They work well in electronics for homes, factories, cars, and new energy.
Three-Terminal Regulator Basics
Definition
A three-terminal regulator is found in many electronic circuits. This device helps keep the output voltage steady, even if the input voltage changes. It is a voltage regulator IC with three pins: input, output, and ground or adjust. You use it to give your circuit a fixed or adjustable voltage. Some common types are the 78xx series for fixed voltages and the LM317 series for adjustable voltages. These regulators are integrated circuits, so they are simple to use and work well in many situations. A basic three terminal voltage regulator can protect your devices from voltage swings.
Tip: Picking a three terminal regulator makes your circuit easier and safer.
Structure
Every three-terminal regulator has three main terminals:
Input: You connect the unregulated voltage here.
Output: You get the regulated voltage from this pin.
Ground (or Adjust): You use this pin as a reference or to set the output voltage.
Inside a basic three terminal voltage regulator, there are important parts:
A potential divider (resistors R1 and R2) checks the output voltage.
An internal reference voltage, often made by a zener diode, keeps things stable.
A series pass transistor acts like a resistor that can change.
An error amplifier compares the output voltage to the reference and makes changes.
Protective circuits, like thermal shutdown and current limiting, keep the regulator safe.
Here is a table that shows the main parts and what they do:
Component | Role in Regulator |
Input Terminal | Gets the input voltage |
Output Terminal | Gives the regulated output voltage |
Ground/Adjust Terminal | Sets the reference or output voltage |
Series Pass Transistor | Controls the output voltage |
Error Amplifier | Keeps the voltage steady |
Reference Voltage | Gives a stable reference |
Protective Circuits | Stops overheating and overload |
You only need a few extra parts, like capacitors, to help with noise and response. This makes three terminal voltage regulators cheap and easy to use.
Function
A three-terminal regulator keeps the output voltage the same. It does this by changing its internal resistance. When the input voltage goes up or down, the series regulator inside changes the current flow. This keeps the output voltage steady. If the load changes, the regulator quickly reacts to keep the voltage right.
For example, if you raise the input voltage, the regulator makes the series pass transistor more resistant. This stops the output voltage from going up. If you lower the input voltage, the regulator lowers the resistance to keep the output voltage from dropping. Both fixed and adjustable three terminal voltage regulators work this way.
Note: You can use diodes at the ground terminal to make the output voltage higher. This trick lets you set custom voltage levels with a basic three terminal voltage regulator.
People pick a three-terminal regulator because it is simple and reliable. You only need input and output capacitors, so your design stays neat and cheap. Compared to switching regulators, a linear regulator like the three-terminal type is easier and costs less for low-power projects. You get steady performance with little work.
How a Three Terminal Fixed Voltage Regulator Works
Internal Components
Inside a three terminal fixed voltage regulator, there are many key parts. These parts work together to keep the voltage steady. Here are the main things inside:
The pass transistor acts like a gate. It controls how much current goes out.
The error amplifier checks if the voltage is right.
The voltage reference gives a steady number for the amplifier to use.
Feedback resistors watch the output and send info back.
Protective circuits stop damage from too much current or heat.
You can see what each part does in this table:
Component | What It Does in the Regulator |
Pass Transistor | Changes how much resistance there is to control the voltage |
Error Amplifier | Checks the voltage and sends a signal to fix it |
Voltage Reference | Gives a steady number for the amplifier to compare |
Feedback Resistors | Send part of the output voltage back for checking |
Protective Circuits | Stop the regulator from getting too hot or having too much current |
All these parts work together to give you a steady voltage every time.
Regulation Principle
A three terminal fixed voltage regulator uses feedback to keep voltage steady. The regulator uses negative feedback to control the output. The error amplifier checks the output voltage and compares it to the reference. If the voltage changes, the amplifier tells the pass transistor to fix it. The pass transistor then changes its resistance.
Negative feedback works like a smart helper. If the input voltage changes, the regulator fixes it fast. The feedback loop always checks and corrects the voltage. You do not have to worry about small changes in input or load. The regulator keeps your devices safe and working well.
Operation
You use a three terminal fixed voltage regulator to get steady power. Here is how it works step by step:
You connect the input voltage to the regulator.
The regulator checks the output with feedback resistors.
The error amplifier compares the output to the reference.
If the voltage is wrong, the amplifier tells the pass transistor to change.
The pass transistor changes resistance to fix the voltage.
Protective circuits watch for too much current or heat and shut down if needed.
Tip: You do not need extra parts to set the voltage. The fixed voltage regulator has a built-in reference, so you always get the same output.
You get smooth power for your devices. This regulator wastes less energy than shunt regulators. It is also easier to use than adjustable regulators. The feedback system inside keeps your circuit safe and simple.
Features and Protections
Built-in Protections
Three-terminal regulators have safety features built in. You do not need extra safety parts. These protections work by themselves.
Overcurrent Protection: The regulator stops too much current. This keeps things from getting too hot. Your devices stay safe from harm.
Overtemperature Protection: If the regulator gets hot, it turns off. It waits until it cools down. This stops damage from heat.
Short-Circuit Protection: If there is a short circuit, the regulator shuts off fast. This keeps your circuit safe from big power surges.
Safe Operating Area (SOA) Protection: The regulator checks its own limits. It makes sure all parts stay safe, even when things change quickly.
Polarity-Reversal Protection: Some regulators protect against wrong wiring. This saves your circuit from mistakes.
These protections help you avoid problems like too much current, heat, or short circuits. You get steady power and longer life for your devices. The regulator keeps voltage steady and stops damage. Your projects stay safe and work well.
Output Stability
A three-terminal regulator gives steady voltage. It works even if the input or load changes. This is important for electronics that need clean power.
Line Regulation
Line regulation means the regulator keeps voltage steady. It does this even if the input voltage goes up or down. Your devices work right, even when power changes.
Load Regulation
Load regulation shows how well the regulator keeps voltage steady. If you add more devices or use more current, the regulator reacts quickly. It keeps voltage close to the same, usually within 1-2% or a few millivolts. This helps protect your electronics from voltage changes.
Ripple Rejection
Ripple rejection means the regulator blocks unwanted noise from the input. This is important for circuits that need clean power, like audio or sensors. The regulator uses special designs to filter out ripple. How well it works depends on the pass device and design. For example, some regulators with BJTs block ripple better at higher voltages. LDOs with MOSFETs may have more ripple at high frequencies. Always check the datasheet for ripple rejection if you need very clean power.
Aspect | Explanation | Example / Note |
Pass Device Type | Ripple rejection depends on transistor type. | LM7805 (BJT) blocks ripple better than some LDO MOSFETs up to 100 kHz. |
Dropout Voltage Impact | Higher dropout voltage blocks ripple better. | Low dropout can mean less ripple rejection in some LDOs. |
Design Technology | New ICs can block ripple better, but old ones may still work well. | LM317 can block ripple better than some new LDOs. |
Frequency Dependence | Ripple rejection changes with frequency and load. | Always check PSRR curves in the datasheet for your project. |
Ease of Use
Three-terminal regulators make building circuits easy. You do not need many extra parts. You can use them in lots of projects.
Simple Circuit Design
You only connect three pins: input, ground, and output. This makes it easy to add a regulator. You do not need hard wiring.
Minimal External Components
Most three-terminal regulators need just a few capacitors. You do not need extra safety circuits. The regulator already has safety built in. This means fewer parts and a neat design.
Easy Implementation
You can use three-terminal regulators in small or big projects. They fit in tight spaces. Beginners like them because they are simple. Professionals trust them for steady and accurate power. You get steady voltage with little work. This saves time and helps your projects work well.
Types and Series
Positive and Negative Regulators
There are two main types of three-terminal voltage regulators. One is positive, and the other is negative. Positive regulators give a steady positive voltage from a higher positive input. Negative regulators give a steady negative voltage from a negative input. Most electronic devices use positive regulators. Negative regulators are needed when a circuit needs both positive and negative voltages. This happens in audio or op-amp circuits.
Positive regulators have NPN transistors inside. Negative regulators have PNP transistors.
Most power supplies use positive regulators.
Negative regulators are best for dual polarity power supplies.
Positive types are easier to find and use in more projects.
Negative types, like the 79xx series, are made for negative voltage rails.
You often see LM7815 (positive) and LM7915 (negative) together in symmetric power supplies.
Positive voltage regulators make up about 70% of the global market. Negative voltage regulators hold 30%. Negative regulators are growing fast because of power-sensitive uses.
Common Series
The 78xx and 79xx series are used in many projects. The 78xx series gives fixed positive voltages like 5V, 9V, 12V, or 15V. The last two numbers in the part number show the output voltage. For example, a 7805 gives 5V, and a 7812 gives 12V. The 79xx series works the same way but gives negative voltages.
Here is a quick look at common series regulators:
Series | Output Voltage | Polarity | Example Use |
78xx series | 5V, 9V, 12V, 15V | Positive | Microcontrollers, sensors |
79xx series | -5V, -12V, -15V | Negative | Audio, op-amp circuits |
You can trust these series for stable, fixed voltages in your designs. They are easy to use and work well in many electronics.
The market for three-terminal voltage regulators keeps growing. There is strong demand in North America, Asia Pacific, and Europe. New trends focus on saving energy, smart devices, and electric cars.
Adjustable Regulators
Sometimes you need more than just fixed voltages. A three-terminal adjustable voltage regulator, like the LM317, lets you set the output voltage to many values. You only need two resistors to set the voltage you want. This makes adjustable regulators great for custom power supplies or projects that need different voltages.
Advantage | Explanation |
Wide Output Voltage Range | You can set voltages from 1.2V to 37V. |
Simple Voltage Setting | Only two resistors are needed for adjustment. |
Better Linearity and Load Regulation | You get stable voltage even when the load changes. |
Integrated Protection Circuits | Built-in safety features keep your circuit safe. |
Programmable Output | You can use it for programmable power supplies or current regulators. |
Higher Ripple Rejection | Adding a filter capacitor improves noise rejection. |
Low Noise and Good Stabilization | You get clean, stable power for sensitive devices. |
You can use an adjustable regulator for many special jobs. It gives you more control than a fixed linear regulator. Adjustable types are found in lab power supplies, battery chargers, and precision circuits.
Applications
Consumer Electronics
Three-terminal regulators are used in many home electronics. These devices need steady power to work well. LDO regulators help phones, tablets, and laptops run better. You also find them in TVs and audio gear. They help cut down on noise and keep things working right. Donghai Semiconductor makes the L7805CV for LED lights and the L7915CV for home machines. These products come in TO-220 and TO-252 packages. These shapes fit well in small spaces.
Device Type | Regulator Model | Application Area |
LED Lighting | L7805CV | Stable power for LEDs |
Home Appliances | L7915CV | Reliable voltage supply |
Smartphones/Tablets | LDO Series | Power for processors |
Audio Equipment | LDO Series | Noise reduction |
Donghai’s voltage regulator ICs are good for cheap and quiet devices. You can use them in headphones, wearables, and IoT gadgets. These regulators help keep your electronics safe and working well.
Industrial Uses
Three-terminal regulators are found in factory electronics. They give steady voltage to control systems and sensors. The L7809CV is good for measuring tools. The L7812CV is used in electric tools. Donghai’s regulators have built-in safety features. These include current limiting and thermal shutdown. These features help your machines last longer and work better.
Welding machines use LDO regulators for steady power.
UPS systems need stable voltage to protect circuits.
Electric tools use the L7812CV for safe use.
Measuring tools use the L7809CV for correct readings.
Donghai’s three-terminal regulators make your factory projects safer and more reliable. Their strong design and special packages, like TO-220 and TO-263, work well in tough places.
Automotive and New Energy
Three-terminal regulators are important in cars and new energy systems. You need steady voltage for electric car controllers and chargers. The L7815CV is great for electric car chargers. Donghai’s regulators help save energy and make batteries last longer. They do this by using less current when not working hard. New LDO technology helps lower noise and boost efficiency.
Electric car converters use LDO regulators for steady power.
Battery management needs exact voltage control.
Car inverters need good regulators for safe use.
Donghai Semiconductor’s voltage regulator ICs, like the L7815CV, support car electronics and new energy projects. You get power that is efficient, low-cost, and reliable for your needs.
Donghai Semiconductor
Company Overview
You want a company that knows about power device technology. Donghai Semiconductor started in 2004 in Wuxi, Jiangsu Province. The factory is big, about 15,000 square meters. It can make 500 million power devices every year. The company works on research, design, packaging, and testing for new semiconductor products. The team has experts with over 20 years of experience in power device research. Donghai has ISO and RoHS certificates to show they care about quality and safety. You can count on them for smart solutions in voltage regulator ics and other power devices.
Product Range
You need choices when picking voltage regulator ics for your project. Donghai offers many three-terminal regulators, like the L7808CV and 78m12A. These can give up to 1.5A of current. They come in different packages, such as TO-220 and TO-252. You can pick output voltages from 5V to 15V. There are also 6V, 8V, 9V, 10V, and 12V options. The regulators use N-type silicon and discrete device technology. You get built-in safety features like thermal overload, short current, and safe output transistor operation. Donghai supports both standard and custom orders, so you can find what you need.
Model | Output Voltage | Max Current | Package | Key Features |
L7808CV | 8V | 1.5A | TO-220 | Thermal, short-circuit protection |
78m12A | 12V | 1.0A | TO-252 | RoHS compliant, safe operation |
L7805CV | 5V | 1.0A | TO-220 | Reliable, easy integration |
The chart shows that Donghai’s voltage regulator ics have many output voltages. This makes it simple to find one for your project.
Technical Strength
You want your devices to be safe and work well. Donghai has advanced labs for testing, checking reliability, and doing research. Their automatic machines help make products fast and keep quality high. The company works on new ideas for making power devices. They help with electronics for homes, factories, new energy, and cars. The technical team creates solutions for solar energy, electric cars, and battery management. You get help from their skills in packaging, discrete device technology, and circuit design. Donghai helps your projects work well and last a long time.
Three-terminal regulators help protect your electronics and make them work well. They give a steady voltage and are simple to add to your projects. These regulators have safety features like shutting down if they get too hot or if too much current flows. If you learn about the pins, voltage choices, and how much current they handle, you can build better circuits. You can start with easy regulator circuits or try adjustable ones for special needs. Companies like Donghai Semiconductor make reliable regulators you can use. Try using three-terminal regulators to get better at building and to make your devices last longer.
FAQ
What is the main use of a three-terminal regulator?
A three-terminal regulator keeps voltage steady in a circuit. It stops voltage from changing too much. This helps your devices work safely and last longer.
How do you connect a three-terminal voltage regulator?
First, connect the input pin to your power source. Next, connect the output pin to your device. Then, connect the ground pin to your circuit’s ground. Most circuits need two capacitors for best results.
Can you adjust the output voltage of a three-terminal regulator?
Some models, like the LM317, let you change the output voltage. You do this by using two resistors. Fixed models, like the 7805, give only one set voltage.
What protections do three-terminal regulators offer?
Three-terminal regulators help stop too much current, heat, or short circuits. These features keep your devices safe and help them last longer.
Where can you use Donghai Semiconductor’s voltage regulator ICs?
You can use Donghai Semiconductor’s voltage regulator ICs in many places. They work in home electronics, factory machines, new energy systems, and cars. These ICs are good for any project that needs steady and safe power.
