LM1084 5-A Low Dropout Positive Regulator

LM1084 is a 5-ampere voltage regulator. It is available in fixed and adjustable voltage versions. There are many voltage regulator ICs available which give a stable and regulated voltage at the output. LM1084 IC is one of them. It is a positive voltage regulator with a pin configuration similar to LM317. It has a low voltage drop at high current value. You can adjust the output voltage by using a network of two resistors connected between adjustable and output terminal. It has its own overload recovery circuit.  Over Current protection, circuit provides output current within a safe operating range. Hence, it consumes very low power.

LM1084 Pin Configuration

Pinout diagram presents that the voltage regulator has three pins. This pin assignment makes it easy to use for power supply and battery charging applications.

LM1084 pinout

It has three pins in total.

  • Pin#01: Input pin of the voltage regulator
  • Pin#02: Output pin of the voltage regulator
  • Pin#03: Adjustable pin connected to two resistors in case of variable voltage and connected to ground in case of fixed voltage.

Features

The features and technical specifications of the LM1084 chip are:

  • It can provide fixed voltages of 3.3V, 5V and adjustable voltage in a range of 0V to 29V.
  • Output current = 5A.
  • The load and line regulations are 0.015% and 0.1%.
  •  75 dB ripple rejection.
  • Its operation is specified in a temperature range of -65 °C to 150 °C.
  • Internal current limiting and thermal protection functions

Where to use LM1084?

This IC is versatile in its applications. You can use this chip in programmable output regulation and local on-card regulation. It can function as a precision current regulator by connecting a fixed resistor between the adjust and output pins. In other standard three-terminal regulators, it is very difficult to achieve a high ripple-rejection ratio. But the adjust pin of this chip can be bypassed which leads to a high rejection ratio.

How to use LM1084?

It is a regulator IC which has a maximum voltage drop of 1.5V. The LM1084 IC is used in two modes which are fixed voltage and adjustable version. In the case of fixed voltage devices, the resistors R1 and R2 shown in the circuit diagram below are integrated inside the devices.

Adjustable output voltage circuit Example

In an adjustable voltage version, the voltage drop across resistor R2 adds to the reference voltage of 1.25V developed between output and adjust pin. This combined voltage is used to set the desired voltage at the output.

LM1084 adjustable voltage power supply circuit example

In some adjustable voltage applications, an additional capacitor is connected between adjust pin and ground. This capacitor is used to increase the ripple rejection. The output capacitor improves the transient response. In applications which require large changes in output current, a large value capacitor is used.  For a ripple rejection, connect a capacitor parallel with R2 in figure 3. It smooths out the ripples from the output and removes the excess noise.

Battery Charger Circuit Example

It can be used as a battery charger where LM1084 IC acts as a constant voltage, constant current part. It senses the voltage potential across the battery and compensates it for the current-voltage. The regulator IC delivers the maximum current which is used to charge the battery. When the battery is near the fully charged state, the voltage potential across Rs and the regulator reduces the current in order to maintain the battery voltage. The circuit diagram is given below.

LM1084 battery charger Circuit example

Equivalents and Alternatives

LM1085, LM317LM723LM7912

LM1084 Applications

Some uses of this versatile IC are listed below:

  • It is used in Switching DC to DC Converters as a post regulator.
  • Their high efficiency makes them suitable for use as linear regulators.
  • They are also used for implementing battery charger circuits.

2D Diagram

The LM1084 IC is available in TO-263 and TO-220 packages. The two-dimensional diagram of the 3-pin TO-220 package along with its dimensions is given. For other packages, check the datasheet.

voltage regulator 2d diagram

Datasheet

LM1084 Datasheet

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