Simple 3 Ampere Adjustable Power Supply Circuit using IC LM350

Imagine a super powered adjustable power adapter for your electronics projects.

This circuit uses a special chip LM350 that acts like a strong and reliable power source.

It can crank out up to 3 amps of juice and adjust the voltage anywhere from 1.25V to 25V.

This makes it perfect for powering all sorts of electronics, testing circuits or even driving small motors.

Basically, it is like a one stop shop for giving your projects the exact power they need.

Circuit Working:

Parts List:

This is a compact adjustable power supply capable of delivering a stable voltage and currents up to 3 amperes.

The circuit is quite conventional, and its voltage output can be adjusted from 1.25V to 25V.

The key component is the LM350 IC which combines a voltage regulator and a power stage.

It includes built in overload protection that activates when power dissipation reaches 30 watts.

The output voltage is set by connecting the ‘adj’ pin of the IC to a voltage divider made of R1 and P1.

The output voltage can be calculated using the formula mentioned below.

Capacitors C1 and C2 improve regulation while diodes D1 and D2 protect the regulator IC when its output is turned off.

The value of resistor R1 is 120Ω ensuring a minimal load current for the IC around 3.4mA to maintain optimal performance.

When constructing the circuit, it is crucial to provide adequate heatsinking for the LM350 IC as its power dissipation can reach around 85 watts.

The heat resistance of a TO 3 package is typically 1.5oC W and the maximum allowable temperature is 150oC.

Using a heatsink with a heat resistance of 1.5oC W, the total heat resistance becomes 4oC W.

At 30 watts dissipation and an outside temperature of 25oC the resulting internal IC temperature is 145oC.

When this dissipation level is reached the internal protection activates, shutting down the IC.

To avoid high dissipation levels, it is advisable to use lower voltage transformers when the required output voltages are low.

For example, if supplying voltages around 9 volts, avoid using a 25V transformer and opt for a lower voltage one e.g.12 or 15V.

Formula:

This formula is usually used to an adjustable voltage regulator using IC LM350 or LM317 in order to calculate the output voltage depending on resistor R1 and P1 values.

V_out = 1.25V x (1 + P1 / R1)

where,

• V_out is the regulators output voltage.
• 1.25V is an internal reference voltage of regulator integrated circuits (like the LM317).
• P1 is a potentiometer used to change the output voltage.
• R1 is the resistor linked to a fixed resistor.

How the formula Operates

Voltage Divider: A voltage divider is made up of R1 and P1.

The ratio of P1 to the total resistance R1 + P1 determines the voltage at the junction of R1 and P1.

Adjusting the Output Voltage: R1 and P1s junction voltage is 1.25V lower than the regulators output voltage.

Range of Adjustment: Depending on the value of R1, you may change the output voltage within a certain range by changing the value of P1 between 0 and 2.5k ohms.

Important Points

There is a clear correlation between the resistor values and the output voltage according to the formula.

The highest value of P1 and the values of R1 determine the output voltage range.

In designs for changeable power supplies, this formula is frequently utilized.

How to Build:

To build a Simple 3 Ampere Adjustable Power Supply Circuit using IC LM350 follow the below mentioned steps:

Circuit Assembly:

• Refer to the circuit diagram for the exact placement of components.
• Connect the LM350 IC to the PCB, ensuring proper orientation.
• Connect the resistors and potentiometer for the voltage divider R1 and P1.
• Connect the capacitors C1 and C2 and diodes D1 and D2 as per the diagram.
• Ensure all connections are secure and correct.

Heatsink Installation:

• Attach the LM350 IC to the heatsink using thermal paste for better heat transfer.
• Ensure the heatsink is properly mounted and can dissipate heat effectively.

Testing and Adjustment:

• Before applying power, double check all connections for correctness and shorts.
• Connect the power supply transformer to the circuit.
• Gradually increase the input voltage and monitor the output voltage using a multimeter.
• Adjust the potentiometer P1 to set the desired output voltage 1.25V to 25V.

Finalization:

• Once the output voltage is set and stable finalize the circuit by securing all components and connections.
• Ensure proper insulation and safety measures are in place.

Usage:

• The adjustable power supply is now ready for use.
• Adjust the potentiometer P1 as needed to change the output voltage within the specified range.

Note:

• Remember, when working with electronics always take necessary safety precautions and consult relevant datasheets and guidelines for the components being used.

Conclusion:

To conclude, the 3 ampere adjustable power supply circuit using the LM350 IC is a practical and versatile solution for electronic enthusiasts and professionals alike.

Its ability to deliver stable output voltages from 1.25V to 25V coupled with a maximum current capacity of 3 amps, makes it suitable for a wide range of applications.

References:

Datasheet IC LM350K