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Showing posts from June, 2009

Variable Power Supply with Transistor

Component parts list:

P1____________500R Linear Potentiometer
P2_____________10K Log. Potentiometer

R1,R2___________2K2 1/2W Resistors
R3____________330R 1/4W Resistor
R4____________150R 1/4W Resistor
R5______________1R 5W Resistor

C1___________3300µF 35V Electrolytic Capacitor (see Notes)
C2______________1µF 63V Polyester Capacitor

D1,D2________1N5402 200V 3A Diodes
D3_____________5mm. Red LED

Q1____________BC182 50V 100mA NPN Transistor
Q2____________BD139 80V 1.5A NPN Transistor
Q3____________BC212 50V 100mA PNP Transistor
Q4 __________2N3055 60V 15A NPN Transistor

T1_____________220V Primary, 36V Center-tapped Secondary
50VA Mains transformer

PL1____________Male Mains plug

SW1____________SPST Mains switch

P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.You can choose the Transfor…

Variable Power Supply

Here a variable power supplycircuit which the output voltage can be adjusted. The stabilizer IC may be changed with different value as needed, example 7815 for 15v maximum voltage.

Component Parts List:
T1 Transformer 10:1 Secondary 24V @ 2A
BR1 Bridge Rectifier 50V PIV 2A rating
C1 4700u (35V)
C2 0.001u
C3 2200u (35V)
C4 0.001u
C5 4.7u (25)
C6 0.01u
R1 10k potentiometer
L1 see text
U1 7805 N.B. This may be changed for different output voltages e.g. 7812 for higher output voltage
ZD1 15V zener @ 1.3W

The specific inductance of the ferrite (core)is important. A core should be chosen to work within the specific frequency as stated by the manufacturer. L1 is a powder core and has 32 turns of 0.75mm wire.

The transformer has a 240V primary and has a secondary rated 24V at 2A. The bridge rectifier contains 4 diodes, their current rating needs to be high with respect to the transformers output current; if not the current may damage the diodes. C1 is the mainfiltering capacitor, the supply is further smoot…