LM350 Güç kaynakları

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3A adjustable regulator using LM350

Description.
This is the circuit diagram of a 3A adjustable power supply using IC LM350K.. LM350K is a very rugged voltage regulator IC with features like thermal regulation, short circuit protection etc. This circuit is designed as per the application notes in the data sheet and was found to be working very fine.This circuit has improved ripple rejection and better stability compared to the elementary voltage regulator using the same IC. The output voltage can be adjusted by using the POT R2.By adjusting R2 the output voltage can be varied between 1.2V and 25V.The diode D2 discharges capacitor C2 when the output is shorted.

Circuit diagram with Parts list.



Notes.

• The circuit can be assembled on a Vero board.
• Input voltage to the regulator can be 30V.
• LM350 must have a heat sink.
• The output voltage is governed by the equation; Vout = 1.25V[ 1+ (R2/R1)]+[(Iadj)(R2)].

 

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This is a compact adjustable power supply that delivers a stable voltage and currents up to 3 amperes. The circuit is very conventional and its voltage output can be varied from 1.25 volts to 25 volts.
The main module is the LM350 IC which integrates a voltage regulator and a power stage. It also has a built-in overload protection which activates at 30 watts of power dissipation. The voltage output is set by connecting the “adj” pin of the IC to the voltage divider made of R1 and P1.

The output voltage can be calculated using the following formula:

1.25V x (1 + P1/R1)

where the P1 value is between 0 and 2.5 KΩ. Capacitor C1 is a common ripple filter while capacitors C2 and C3 improves the regulation. The diodes D1 and D2 serves as protection for the regulator IC when the IC output is turned off. Resistor R1 is 120Ω. This ensures that the minimal load current for the IC (around 3.4mA) is high enough to maintain good performance.

3 Ampere power supply circuit schematic


One thing that is most important in building the electronic circuit: provide adequate heatsink for the LM350 IC. The power dissipation at the IC is very high, around 85 watts.
Consider that the heat resistance of a TO-3 package is 1.5oC/W and the maximum allowable temperature is 150oC. If a heatsink is used with a heat resistance of 1.5oC/W, when the total heat resistance is 4oC/W. At 30 watts dissipation and 25oC outside temperature, the resulting internal IC temperature is 145oC. Once this dissipation level is reached, the internal protection activates shutting down the IC.

Adjustable Power supply PCB


One way to avoid high dissipation levels is to use a lower voltage transformers when needed output voltages are low. To put it simply: if you are using the circuit to supply voltages around 9 volts, do not use a 25 volts transformer but use a lower voltage one instead (e.g. 12 or 15 volts).

 

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Variable Power Supply - 3A

Here's another linear power supply circuit. Although it is a mini power supply unit, it is able to deliver up to 3 A at an output voltage of 1.25 to 25 V. It is based on LM350, which is a popular linear regulator. The regulator has on-chip overload protection that comes into operation when the dissipation in the device reaches 30 W. The output voltage, Uo, is calculated from

Uo = [1.25 (1 + P1/R1)] V

where P1 and R1 are in ohms (the value of P1 is measured between the wiper and the junction with R1, i.e., 0...2.5 KΩ).

3A variable power supply schematic
C1 is a conventional filter capacitor, while C2 and C3 improve the regulation. Protection diodes D1 and D2 ensure that at switch-off the potential at the output of IC1, is more positive than that at its input.

It is essential that IC1, is mounted on a large heat sink rated at about 1 K/W .

When only low output voltages are needed, it makes sense to use a mains transformer with a lower secondary voltage (for Uo = 5 V, the secondary voltage should be 9 V). When a 24 V secondary is used, and the required output voltage is 1.25 V, the maximum output current is 1 A, otherwise the maximum dissipation of the LM350 is exceeded, and the internal protection will switch off the regulator. When the secondary voltage is 9 V, and Uo = 1.25 V, the maximum load current amounts to 2.5 A.