You use a three-terminal regulator by connecting the input to your unregulated voltage source. Connect the ground pin to the circuit ground. Connect the output to your load. Pick the right type, fixed or adjustable, to fit your needs. Always check the pin setup and use the right capacitors. If you forget about the small quiescent current in the ground pin, your current math may be wrong. Using the wrong capacitor can make noise or interference. At Donghai Semiconductor, we design our three-terminal regulator products to help you avoid these common mistakes.
Key Takeaways
Pick the right regulator type for your project. Use fixed regulators for common voltages. Use adjustable regulators for custom voltages.
Connect the input, ground, and output pins the right way. Put capacitors close to the pins. This helps your circuit stay stable and quiet.
Use a heatsink to handle heat from power loss. This keeps your regulator cool and working well.
Use built-in protections like current limiting and thermal shutdown. These features help keep your circuit safe.
Test your circuit with real loads. Check your wiring twice to avoid mistakes. This helps make sure your voltage stays steady.
Choosing a Three-Terminal Regulator
Picking the right three-terminal regulator is important. It helps your electronic circuit work well. You must choose between fixed voltage regulators and adjustable 3-terminal positive voltage regulators. Your choice depends on your project’s voltage and current needs. Knowing the differences helps you pick the best voltage regulator ICs for your job. This is true if you power a simple LED circuit or build a complex power supply for instruments.
Fixed Voltage Regulators
Fixed voltage regulators give one steady output voltage. The 78xx series is used for positive voltages. The 79xx series is used for negative voltages. The 78xx series has models like L7805CV (for LED), L7812CV (for power tools), L7815CV (for chargers), and L7809CV (for instrumentation). These regulators are simple to use. You only need a few extra capacitors to keep them stable.
Tip: Use fixed voltage regulators if your circuit needs a common voltage like 5V, 9V, 12V, or 15V. This makes your design easy and dependable.
Here is a table that compares fixed and adjustable regulators:
Parameter | Fixed Voltage Regulators (78xx, 79xx series) | Adjustable Voltage Regulators (LM317 series) |
Output Voltage | Fixed (like 5V for 7805, 12V for 7812) | Adjustable from 1.25V to 37V with resistors |
Output Current | Usually up to 1A | Up to 1.5A |
Dropout Voltage | About 2V | About 2V |
Efficiency | Low (30-60%) | Low (30-60%) |
Heat Dissipation | High, needs heat sink | High, needs heat sink |
External Components | Few (just some capacitors) | Needs resistor network for voltage setting |
Application Use | Simple, fixed voltage needs | Flexible voltage needs, custom outputs |
You can use fixed voltage regulator models in many ways. The table below lists some popular models and what they are used for:
Regulator Model | Type | Output Voltage | Key Features | Typical Applications |
7805, 7812 (78xx series) | Fixed linear regulator | 5V, 12V fixed | Simple 3-pin design, needs few extra parts | Consumer electronics, general power supply |
L7805CV | Fixed linear regulator | 5V | Steady output, easy to use | LED circuits |
L7812CV | Fixed linear regulator | 12V | Reliable, strong | Power tools |
L7815CV | Fixed linear regulator | 15V | Handles more current | Chargers |
L7809CV | Fixed linear regulator | 9V | Gives steady voltage | Instrumentation |
79XX series | Fixed negative linear regulator | -5V, -12V fixed | Makes negative voltage rails | Audio circuits, amplifier boards needing two supplies |
L7915CV | Fixed negative linear regulator | -15V | Negative voltage supply | Home appliances |
Note: Fixed voltage regulators like L7805CV and L7812CV work well for Donghai Semiconductor’s consumer electronics and industrial products.
You will see fixed voltage regulators in many places:
Adjustable Regulators
Adjustable 3-terminal positive voltage regulators are flexible. The LM317T positive voltage regulator is a favorite. You can set its output voltage from 1.25V to 37V by changing two resistors. This is great for custom power supplies, battery chargers, and test equipment.
Tip: Use an adjustable regulator if you need a special voltage or want a variable power supply.
The LM317 keeps about 1.25V between its output and adjust pin. You set the output voltage with a voltage divider made of two resistors. If you use a potentiometer instead of one resistor, you can change the output voltage easily. This is a common way to use adjustable regulators.
Here is how to set the output voltage:
Put a fixed resistor (R1) between the output and adjust pin.
Connect a second resistor (R2) or potentiometer from the adjust pin to ground.
The output voltage depends on the ratio of R1 and R2.
You can use adjustable regulators for:
When you pick a three-terminal regulator, think about these things:
Criterion | Explanation |
Input Voltage vs Output Voltage | Input voltage must be higher than output voltage by at least the dropout voltage. |
Current Rating | The regulator must handle the highest load current. |
Power Dissipation | Figure out (Vin - Vout) × Load Current to estimate heat. |
Thermal Resistance (Theta-JA) | Use datasheet values to guess temperature rise. |
Maximum Junction Temperature | Make sure the regulator stays under its top temperature (usually 125°C). |
Low Dropout Voltage (LDO) | Pick LDO regulators for small input-output voltage gaps. |
Quiescent Current & Noise | Check these for sensitive analog or battery-powered circuits. |
Note: Donghai Semiconductor has many voltage regulator ICs, including fixed and adjustable types, for consumer electronics, industrial equipment, and automotive electronics.
Wiring and Installation
It is simple to set up a three-terminal regulator. You just need to follow some easy steps. Connect each pin the right way. Put the capacitors in the best places. This keeps your circuit working well and quiet.
Pinout and Connections
First, check the pinout for your regulator. Most three-terminal regulators have three pins: Input, Ground, and Output. The order of the pins can change with the package type. Always look at the datasheet before you start.
Here is an easy wiring guide:
Connect the Input Pin
Connect the input pin to your DC voltage source. The input voltage should be at least 2 volts higher than the output.
Connect the Ground Pin
Connect the ground pin to your circuit’s ground. This pin gives the reference for the output voltage.
Connect the Output Pin
Connect the output pin to your load. This pin gives the regulated voltage.
Tip: Always check your connections twice. If you mix up the pins, the regulator will not work. You might get the same voltage at the output as the input. Sometimes, you may get no voltage at all. If the ground is not connected well, the output voltage can be wrong. Bad soldering or broken wires can cause the regulator to get too hot or break.
Here is a table that shows pinouts for common regulator packages:
Package Type | Pin 1 | Pin 2 | Pin 3 |
TO-220 | Input | Ground | Output |
TO-252 | Input | Ground | Output |
TO-92 | Input | Ground | Output |
If you use Donghai Semiconductor regulators, check the datasheets for the pinout.
Capacitor Placement
Capacitors help the regulator stay stable and quiet. You need to use the right size and put them in the right spots.
Input Capacitor:
Put a 0.33 µF ceramic capacitor close to the input pin. This helps block noise from your power source. You can also add a 10 µF electrolytic capacitor for better results.
Output Capacitor:
Put a 0.1 µF ceramic capacitor near the output pin. This keeps the output voltage steady. A 10 µF electrolytic capacitor helps with quick changes in load.
Smoothing Capacitor:
Use a smoothing capacitor to lower voltage ripple. Place it close to the regulator output and your load.
Note: Where you put the capacitors is very important. If they are far from the regulator, you may get more noise and less stability. Always keep capacitors close to the pins. Keep them away from heat. Decoupling capacitors can trap high-frequency noise and stop it from spreading.
Here is a quick checklist for placing capacitors:
Use ceramic capacitors for low ESR and small size.
Add electrolytic capacitors for better response to changes.
Make sure the voltage rating is at least 1.5 times your input voltage.
Place capacitors close to the regulator pins and load.
Group noise-sensitive loads and use local decoupling capacitors.
If you follow these steps, your three-terminal regulator will work well and quietly. You will avoid problems like wrong output voltage, noise, and instability. Donghai Semiconductor suggests using these tips for all their regulator products.
Key Features and Protections
Three-terminal regulators have features that keep circuits safe. These features help your projects work well and last longer. At Donghai Semiconductor, our voltage regulator ICs have these protections. This helps you build strong electronic systems.
Current Limiting
Current limiting stops your devices from using too much current. If your load tries to take more current than allowed, the regulator helps. It uses a sensing resistor and a transistor to check the current. When the current gets too high, the transistor turns on. This stops the current from going higher. The output current stays at a safe level. If you keep adding more load, the output voltage drops. But the current does not go past the safe limit. You can find this feature in battery management systems and motor drivers.
Here are some current limits for popular regulators:
Regulator Model | Typical Max Output Current |
78L05 | 100 mA to 150 mA |
LM7805 | 1 A |
78M05 | 0.5 A |
78S05 | 2 A |
78T05 | Up to 3 A |
Tip: Always look at the datasheet for the current limit. This helps you choose the right part for your project.
Thermal Shutdown
Thermal shutdown keeps your regulator from getting too hot. If the inside of the regulator gets too warm, it shuts down or lowers the output current. This protects your circuit from heat damage. You do not need extra parts for this. The regulator does it by itself. Your circuit will stay safe, even if it gets hot or the load goes up.
Voltage Regulation
Voltage regulation gives your circuit a steady output voltage. The regulator uses feedback loops and control circuits to keep the voltage stable. Changes in input voltage or load do not change the output much. Your devices get reliable power. The type of regulator, like fixed or adjustable, changes how well it controls voltage. Low Dropout Regulators (LDOs) work well when the input voltage is close to the output voltage.
Some things that affect voltage regulation are:
Type of regulator (fixed, adjustable, LDO)
Internal feedback and control circuits
Dropout voltage
Load and input voltage changes
Thermal protection features
Note: Donghai Semiconductor voltage regulator ICs give steady voltage, strong current limiting, and automatic thermal shutdown. These features help you make safe and reliable electronic circuits.
Power Dissipation and Heatsinking
When you use a three-terminal regulator, you need to think about heat. Regulators change extra voltage into heat. If you do not control this heat, your device can get too hot. It might stop working. Donghai Semiconductor helps you learn how to keep your regulator cool and safe.
Calculating Power Loss
You can find out how much heat your regulator makes with a simple formula. Subtract the output voltage from the input voltage. Then multiply that number by the current your load uses. This shows how much power is lost as heat.
For example, if your input voltage is 5V and your output voltage is 3.6V, and your load uses 140mA, you do this:
Power Loss = (5V - 3.6V) × 0.14A = 0.196W
This means your regulator makes 0.196 watts of heat. If your load current is much bigger than the quiescent current, you can ignore the small extra current. Always check the worst-case situation. If your input voltage goes up or your load gets bigger, the heat will go up. You must make sure your regulator can handle this heat.
Tip: Use the formula Power Loss = (Vin - Vout) × Iload for quick checks. Always plan for the highest load your circuit might have.
Heatsink Selection
You need a heatsink if your regulator makes lots of heat. A heatsink is a metal piece that helps move heat away from the regulator. You can use a folded aluminum box or the metal case of your device. Use insulation washers and mica sheets to keep the regulator safe from electrical shorts.
If your regulator gets very hot, use a bigger heatsink or put it on the enclosure. Good airflow helps cool things down. Sometimes, you can use a resistor before the regulator to drop some voltage and share the heat. This lets you use a smaller heatsink on the regulator.
Here are some tips for picking a heatsink:
Use a big metal piece for better cooling.
Make sure the heatsink does not touch any electrical parts.
Add airflow if you can.
Share heat with resistors if needed.
Power Dissipation (W) | Heatsink Recommendation |
< 0.5 | Small metal tab or PCB copper |
0.5 – 1.5 | Folded aluminum or small finned |
> 1.5 | Large external heatsink, airflow |
Note: Donghai Semiconductor designs regulators to work with many heatsink types. Always check your regulator’s datasheet for mounting advice.
A good heatsink keeps your regulator cool. Your circuit will last longer and work better. You protect your devices and get the best performance from your three-terminal regulator.
Application Circuits
At Donghai Semiconductor, there are many ways to use a three-terminal regulator. You can make a variable voltage power supply. You can also increase output current or fix common problems. Let’s see some popular circuit examples.
Variable Voltage Power Supply
You can build a variable voltage power supply with an LM317. This setup lets you change the output voltage for different needs. Here is how you do it:
Connect the input pin of the LM317 to your DC source.
Use two resistors. R1 goes from the adjustment pin to ground. R2 goes from the output pin to the adjustment pin.
The output voltage uses this formula:
Vout = 1.25V × (1 + R2/R1)
If you use a potentiometer for R2, you can adjust the voltage.
Add input and output capacitors close to the pins for better stability.
You can set the output from 1.25V up to about 30V. This depends on your input voltage. This power supply is good for testing circuits, charging batteries, or powering devices that need different voltages. You can also use two LM317s for both current and voltage control. Always use a heat sink to keep the regulator cool.
Common uses for a variable voltage power supply:
Testing electronic parts
Powering small motors
Driving LEDs and sensors
Charging batteries
Boosting Output Current
Sometimes, you need more current than one regulator can give. You can boost the output current by adding a power transistor. Here is a simple way to do it:
Use a PNP or NPN transistor as a helper.
Put a resistor between the regulator output and the transistor base to sense current.
When the load needs more current, the transistor helps supply it.
This method lets your power supply give more current. Always add a heat sink to the transistor. Use protective diodes and check that the transistor does not get too hot. This setup is used in power supplies for bigger loads.
Troubleshooting Tips
You might have problems with your circuit. Here are some steps to help you fix them:
Check that your input voltage is steady and high enough.
Make sure input and output capacitors are the right value and close to the regulator.
Check all wiring and solder joints for good connections.
Make sure the load current does not go over the regulator’s rating.
Use a good heat sink to stop overheating.
Look for damage, like output voltage matching the input or no regulation.
Replace broken parts if needed.
Tip: If your output voltage is not steady, try bigger capacitors or move them closer to the regulator pins.
These tips help your three-terminal regulator circuits work well. For good results, always follow best practices and check your work. At Donghai Semiconductor, we suggest using our regulators for your next variable voltage power supply or fixed voltage power supply project. Try these circuit ideas and see how easy it is to get steady, adjustable power for your electronics.
You can get good results with three-terminal regulators if you follow some simple steps. Pick an input voltage that is 2 to 3 volts higher than your output. Put the input and output capacitors close to the pins. This helps lower noise in your circuit. Use a heat sink to handle extra heat from power loss. Always read the datasheet and check your wiring before turning on your circuit. Test your circuit with real loads to make sure it works right. You can find more help in datasheets and learning guides. Donghai Semiconductor suggests these tips so your circuits stay safe and work well.
FAQ
How do you choose the right three-terminal regulator for your project?
First, think about how much voltage you need. Next, check how much current your circuit uses. Then, pick either a fixed or adjustable regulator. Donghai Semiconductor has many choices for electronics, factories, and cars.
What happens if you connect the pins incorrectly?
Your circuit might not work at all. You could get no voltage or the wrong voltage. Always read the datasheet and check the pin layout before you start wiring.
Why do you need capacitors with a voltage regulator?
Capacitors help keep the voltage steady. They block noise and stop voltage spikes. Put them close to the regulator pins for the best results.
Can you use a three-terminal regulator for battery charging?
Yes, you can use adjustable regulators like LM317 for charging batteries. Set the output voltage to match your battery. Always watch the temperature and current while charging.
How do you keep your regulator cool during operation?
Use a heatsink or a metal tab to move heat away. Make sure air can flow around the regulator. Figure out how much power is lost and choose the right heatsink size.
