A voltage regulator is an electronic device that is found in most electronic devices. The main function of this device is to maintain the fixed output voltage to make sure that the voltage stays within suitable limits. These devices are commonly used in different types of motor vehicles to ensure equivalent generator output voltage to the electrical load & also to ensure the battery charging requirements. These are also used within electronic apparatus where extreme variations in voltage could be harmful. This article provides brief information on one of the LM series voltage regulators namely; the LM340 voltage regulator, its working, and its applications.
What is the LM340 Voltage Regulator?
The LM340 is a three-terminal voltage regulator that uses internal thermal shutdown, current-limiting & safe-area compensation to make it essentially durable. They can deliver above the 1.5 Amps output current if sufficient heat sinking is given so this is known as a 1.5A fixed voltage regulator. These voltage regulators are used in a wide range of applications like; local regulation for noise elimination, and distribution problems coupled through single-point regulation. These regulators are used with exterior components to get modifiable output voltages & currents. To make the whole series of regulators very easy to utilize and reduce the number of exterior components then considerable attempt was made.
Pin Configuration:
The pin configuration of the LM340 voltage regulator is shown below. This IC includes three pins and each pin functionality is discussed below.
LM340 Pin Configuration
- Pin- 1 (Input): This is an input voltage pin.
- Pin- 2(GND): This is a ground pin.
- Pin- 3 (Output): This is an output voltage pin.
Features & Specifications:
The features and specifications of the LM340 voltage regulator include the following.
- This voltage regulator has three terminals.
- It is available in the SOT-223 package.
- The output current of this regulator is up to 1.5 A.
- It is accessible in fixed 5V, 12V & 15V Options.
- ±2% o/p voltage tolerances at TJ = 25°C.
- Line regulation per voltage at 1A load is 0.01%.
- It has short circuits, internal thermal overload, and SOA protection.
- Output capacitance is not necessary for stability.
- The type of mounting is Through-Hole.
- Its weight is 2.299997 grams.
- Its operating temperature ranges from 0°C to 125°C.
- The packaging type is Tube.
- Moisture Sensitivity Level or MSL is 1 (Unlimited).
- The terminal finish is Tin/Lead or Sn/Pb.
- The terminal pitch is 2.54mm.
- Its current rating is 1A.
- Its maximum input voltage is 35V.
- Its output voltage is 15V.
- Its minimum voltage supply is 17.5V.
- Its quiescent current is 8mA.
- Its accuracy is 2 %.
- Its maximum dropout voltage is 2V at 1A.
- Its Power Supply Rejection Ratio or PSRR is 80dB.
- Its height x length x width is 4.7mm x 14.986mm x 10.16mm.
- Its thickness is 4.572mm.
LM340 Series Voltage Regulator Block Diagram
The block diagram of the LM340 voltage regulator is shown below. In the following diagram, the Vref reference voltage simply drives the op-amp’s non-inverting input.
LM340 Block Diagram
Here for the operational amplifier, there are various voltage gain stages are used where the high gain assists the operational amplifier to make the error voltage in between the two terminals to be approximately zero. So, the inverting input terminal value is similar to the non-inverting terminal. Therefore, the flow of current throughout the potential divider is written as
I = Vref/R2
The resistor ‘R2’ in this block diagram is not an exterior component connected to the regulator IC, however, an internal resistor is built within the IC while designing. Thus the o/p voltage is written as;
Vout = Vref/R2 (R1 + R2)
This output voltage shows the output of the voltage regulator that can be controlled simply by putting preferred R1 & R2 values. This voltage regulator IC includes a series pass transistor that handles above 1.5 A of load current.
Similar to other voltage regulator ICs, this IC has current limiting & thermal shutdown options features. The thermal shutdown feature of this IC turns off this IC once the internal temperature of the voltage regulator IC increases over its preset value. This temperature rise may be because of extreme ambient temperature, external voltage, or heat sinking. The value of the preset cut-off temperature for this IC is 175° C.
LM340 Series Voltage Regulator Circuit Diagram
The LM340 voltage regulator circuit diagram is shown below. In this circuit, the LM340 IC includes three pins where Pin 1 is the input, pin2 is GND and Pin 3 is the output.
LM340 Circuit Diagram
Whenever there is somewhat of a distance from the LM340 IC to the filter capacitor of the unregulated power supply, then unwanted oscillations may occur in this voltage regulator IC because of lead inductances in the circuit. To remove these unwanted oscillations, the ‘C1’ capacitor has to be connected to the pin 1 of the IC.
Sometimes, the ‘C2’ capacitor is used to develop the circuit’s transient response. In the LM 340 series regulators, any device requires a minimum 2 to 3V input voltage which is higher as compared to the regulated output voltage, or else, it will discontinue regulating. In addition, there is a highest input voltage due to extreme power dissipation.
Applications
The applications of the LM340 voltage regulator include the following.
- The LM340 is used as a fixed voltage regulator within a broad range of applications like local regulation for the noise elimination & distribution issues associated with single-point regulation.
- These regulators are used in AC inventors, HVAC systems, solar energy string inverters, SMPS post-regulation, industrial power supplies, etc.
- These are used in test & measurement equipment.
- These regulators are used in brushless & brushed DC motor drivers.
- These are used in error amplifiers, low o/p voltage switching power supplies, accuracy current limiters, monitoring of voltage, analog & digital circuits, current source & sink circuits, etc.
- These voltage regulators are used in adaptable current or voltage linear & switching power supplies.
Please refer to this link for the LM340 Voltage Regulator Datasheet.
Thus, this is an overview of the LM340 voltage regulator, pinout, specifications, circuit, and its applications. The LM340 is a positive voltage regulator including three terminals which uses internal thermal shutdown, safe-area compensation & current-limiting which makes them durable. This voltage regulator delivers over the 1.5A output current when sufficient heat sinking is provided. These regulators don’t need any outside components for regular operation but, by connecting a few parts, we can enhance the transient response to provide an uneven output voltage (or) improve the output current. Here is a question for you, what is what is LM314 IC?