# 2.5-30V Variable Power Supply Circuit

The * variable power supply circuit* presented in this

**allow to supply a consumer with a 60-70 W power consumption and a range of voltage between**

*schematic**with a current from*

**2.5-30V****.This variable power supply has a shortcircuit protection and a scale indication for output voltages and current.**

*0.6A to 2.5 A*The capacitor filter for input voltage must have a value between 3300-6800uF.

Error amplifier of the source it's made with a 741 operational amplifier which is supply with a 40 V tension from D7 , D8 diode.

The reference voltage it's given from an other 741 amplifier which give a very stable reference voltage.

Ic U1 commands a darlington connection made by T5 and T3 which command the power transistors 2n3055.

The limit current is given by T6 trough Pot2 which allow to chance the limit current.

When the current it's over the limit the lamp is lighting.

The 2N3055 transistors must be mounted on a heatsink with a 400cm 2 area.

The transformer must give 30 volts and 3 Ampers.

**Components**

Notations | Value |

R1,R6 R2 R3 R5 R7,R9,R11 R8 R10 R12,R13 R14 R15 R17 C1 C2 C3,C4,C5 D1,D2,D3,D5,D6 D4 D7,D8 D9 U1,U2 Pot1 Pot2 Q2,Q4 Q1,Q3 Q5,Q6 S1 bec mA |
0.33 ohm Rezistor/5W 1 ohm Rezistor /10W 330 ohm Rezistor /10W 300 ohm Rezistor /3W Se aleg a.i la cap de scala sa arate val maxima 2.7k ohm Rezistor 12k ohm Rezistor 5.6k ohm Rezistor 22k ohm Rezistor 6.8k ohm Rezistor 4.7k ohm Rezistor 220µF/40V 3300µF/40V 10nF 1n4001(1n4004) Bridge Dioda zener 20V Dioda zener 5.1V Ad741 100k lin 500 ohm lin 2n3055 Bd135(Bd139) Bc107 switch lamp 24V 0.05A miliampermetru |

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