78L05 Pinout: Understanding its Features and How to Use One

78L05 Overview and Key Specifications

The 78L05 is a three-terminal positive voltage regulator that outputs a steady +5V from a higher input voltage. Some of the key specifications of the 78L05 include:

Parameter	Value
Output Voltage	+5V
Input Voltage Range	+7V to +20V
Output Current (Max)	100mA
Dropout Voltage	2V
Operating Temperature Range	0°C to +125°C

The 78L05 is available in both TO-92 and SO-8 packages. It provides a simple, inexpensive solution for powering 5V electronics.

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78L05 Pinout and Pin Functions

The 78L05 voltage regulator has three pins:
1. Input
2. Ground
3. Output

Here is the 78L05 pinout diagram for the common TO-92 through-hole package:

      _____
IN —-|     |—- OUT
      78L05  
GND --|     |   
      ‾‾‾‾‾

And here is the 78L05 pinout for the SO-8 surface mount package:

 _______________________
|                       |
|         78L05         |
|                       |
| IN   NC  GND  OUT  NC |
|_______________________|

The functions of each 78L05 pin are as follows:

Input (IN)

This is where the higher, unregulated input voltage is applied. The 78L05 requires an input voltage that is at least 2V higher than the regulated 5V output. Typically a 9V battery or 12V power supply works well.

Ground (GND)

The ground pin connects to the 0V or negative side of the power supply. This pin is the reference for the 5V output.

Output (OUT)

This is the regulated +5V output from the 78L05 that powers your load circuit. The 78L05 can supply up to 100mA of current.

Note that the SO-8 package has two additional “no connect” (NC) pins that are not used.

Basic 78L05 Circuit

Using a 78L05 in your project is very straightforward. Here is the typical circuit for using a 78L05 to provide 5V power:

        ┌────────┐
     ───┤ IN  OUT├──┬─── +5V
        │   78L05│  │
        │     GND├──┴─── GND
        └────────┘
              │
            ─┬┴┬─ 
             │││  100nF  
             │││
             GND

The input voltage, which must be at least 7V, is applied to the 78L05 IN pin. The regulated 5V output appears on the OUT pin.

Connect the GND pin to the negative or 0V side of your power supply and circuit. It’s also good practice to place a 100nF ceramic capacitor close to the GND and OUT pins to improve stability and reduce high frequency noise.

That’s really all there is to it! With this simple circuit, you now have a stable 5V supply to power your electronics project.

Calculating Resistor Values for LEDs

One common use of the 78L05 is to power 5V LEDs. To limit the current through an LED to a safe value, you need a current-limiting resistor in series. Here’s how to calculate the resistor value:

The formula is:

R = (Vs - Vf) / I

Where:
– R is the resistor value in ohms
– Vs is the supply voltage (5V in this case)
– Vf is the forward voltage of the LED (usually around 2V for red, 3V for blue and white)
– I is the desired LED current in amps (a common value is 20mA or 0.02A)

For example, to power a red LED at 20mA from 5V, the calculation is:

R = (5V - 2V) / 0.02A
  = 3V / 0.02A 
  = 150 ohms

So a 150 ohm resistor in series with the red LED will limit the current to a safe 20mA value when powered by the 5V from a 78L05.

78L05 Power Dissipation and Heatsinking

An important consideration when using any linear voltage regulator like the 78L05 is power dissipation. The 78L05 has to dissipate power equal to the voltage dropped multiplied by the load current.

The power dissipated in the 78L05 is:

P = (Vin - Vout) × Iout

Where:
– P is power in watts
– Vin is the input voltage
– Vout is the regulated output voltage (5V)
– Iout is the load current in amps

For example, if powering the 78L05 with 12V and drawing the full 100mA load:

P = (12V - 5V) × 0.1A
  = 7V × 0.1A
  = 0.7W

The 78L05 in a TO-92 package can dissipate around 0.5W without a heatsink. Above that, the chip can get very hot and go into thermal shutdown or fail. If your 78L05 is dissipating more than 0.5W, consider:

Adding a heatsink to the 78L05 to help dissipate the heat. A small clip-on TO-92 heatsink can work wonders.
Reducing the input voltage closer to 7V to minimize the voltage dropped and power dissipated in the regulator.
Using an alternative switching regulator which is much more efficient, especially with higher input voltages and currents.

78L05 Dropout Voltage

The dropout voltage of a linear regulator like the 78L05 is the minimum difference between the input and output voltage for the regulator to still maintain regulation.

The 78L05 has a dropout voltage of around 2V. This means the input voltage must be at least 2V higher than the 5V output for the 78L05 to function properly.

If your input voltage drops too close to the 5V output voltage, the 78L05 will “drop out” of regulation and the output voltage will sag below 5V. This is important to keep in mind if your input voltage is variable or could drift lower over time, like a battery discharging.

To avoid dropout issues, ensure your 78L05 input voltage stays above 7V at all times. A 9V battery is a good fit for the 78L05 to provide some headroom.

78L05 Protection Features

The 78L05 includes several built-in protection features that help make it robust and reliable:

Current limiting: The 78L05 limits its output current to a safe value (around 200mA) if the load tries to draw too much. This helps protect the 78L05 and your circuit from damage due to short circuits or overloads.
Thermal shutdown: If the 78L05 gets too hot, it will automatically shut down to prevent damage. It will recover and start working again once it cools off.
Safe operating area protection: The 78L05 is designed to operate within a safe range of voltage and current. It will automatically limit the output to stay within the safe operating area.

While these protection features help make the 78L05 easy to use, it’s still important not to push a linear regulator to its limits. Follow the power dissipation and dropout voltage guidelines for best results.

78L05 vs. Other 5V Regulators

The 78L05 is just one of many types of 5V voltage regulators. Some key advantages of the 78L05 are:

Simple to use 3-pin design
Inexpensive and widely available
Decent 100mA output current
Robust with built-in protection features
Available in both through-hole and surface mount packages

Some potential disadvantages of the 78L05 compared to other 5V regulators:

Relatively high dropout voltage (2V) compared to some LDO (low dropout) regulators
Not as efficient as switching regulators, especially at higher input voltages and currents
Maximum 100mA output current may be limiting for some projects

Ultimately, the 78L05 is a solid choice for many 5V applications up to 100mA. For projects with higher power needs or efficiency concerns, consider a switching regulator. For ultra-low dropout needs, an LDO regulator may be a better fit.

78L05 FAQs

Here are answers to some frequently asked questions about the 78L05 voltage regulator:

What is the 78L05 used for?

The 78L05 is a linear voltage regulator that provides a fixed +5V output from a higher input voltage. It is commonly used to provide a regulated 5V power supply for digital logic circuits, microcontrollers, sensors, LEDs, and other electronics projects that require 5V.

How much current can a 78L05 supply?

The 78L05 can supply a maximum output current of 100mA. This is suitable for powering small projects and circuits, but may not be enough for devices that require more power. Check the current requirements of your load and ensure it does not exceed 100mA when using a 78L05.

What is the minimum input voltage for a 78L05?

The 78L05 requires an input voltage at least 2V higher than the regulated 5V output. This 2V difference is called the dropout voltage. Therefore, the minimum recommended input voltage for a 78L05 is 7V to ensure proper regulation. A common choice is a 9V battery.

How do I know if my 78L05 is overheating?

The 78L05 can get quite hot when dropping a large voltage and supplying significant current. If the 78L05 is too hot to touch, it is likely overheating. You can also calculate the power dissipation and compare it to the 0.5W rating. If overheating, add a heatsink, reduce the load current, or lower the input voltage if possible.

Can I adjust the 78L05 output voltage?

No, the 78L05 is a fixed 5V regulator. The output voltage is internally set and cannot be adjusted. If you need an adjustable voltage, consider a variable regulator like the LM317. If you need a different fixed voltage, consider another regulator in the 78xx series like the 7803 (3.3V), 7806 (6V), 7808 (8V), or 7812 (12V).

Conclusion

The 78L05 is a simple and reliable choice for powering your 5V electronics projects up to 100mA. By understanding the 78L05 pinout, features, and usage guidelines, you can harness this versatile voltage regulator in your designs.

Remember to keep the input voltage above 7V, watch the power dissipation and dropout voltage, and add a capacitor on the output for best stability. With the 78L05, it’s easy to add a robust 5V power supply to your project.

I hope this article has been a helpful introduction to the 78L05 voltage regulator. Happy building!