Digital Bechtop Power Supply (2)
soldering, sawing and drilling
Published in issue 305, December 2001
The construction of the Digital PSU requires extra care and precision. Just like the electronics inside, the mechanical construction and overall finish of the instrument should meet professional requirements.As indicated at the outset, there are two versions of the power supply that you can build. However, we have decided not to produce special circuit board and front panel layouts for the smaller power supply and concentrated on the larger 2.5 A unit.For the 2.5 A power supply a metal enclosure 200 mm (width) by 180 mm (depth) by 100 mm (height) and a 24 V 80 VA toroidal transformer are used, with all the parts of the enclosure securely connected to earth. A mains filter must also be fitted, or else the microcontroller may reset in the event of mains interference. The circuit board is fixed to the front panel with bolts, while the base simply carries the toroidal transformer (and possibly also, as shown in the photograph, the mains filter).
2.5 A version (1 A version in brackets)
Resistors:
(* Metal film, 1% tolerance)
R1 = 220Ohm , 5W
R2 = 330Ohm , 0.5W
R3 = 150Ohm
R4 = 100kOhm
R5 = 330Ohm (1kOhm 8)
R6 = 1kOhm , 0.5 W
R7,R18,R23 = 1kOhm *
R8,R17 = 39kOhm *
R9,R10,R13,R14,R40,R41,R43 = 10kOhm
R11,R12 = 47kOhm
R15,R16 = 10kOhm *
R19 = 8kOhm 2
R20,R39 = 1kOhm
R21 = 1kOhm * (0Ohm )
R22 = 18kOhm * (39kOhm *)
R24-R34 = 1Ohm * 0.6W
R35-R38 = 100kOhm *
R42 = 47kOhm
R44 = 3kOhm 3
R45,R46,R47 = 0Ohm 51, 0.5 W (not fitted)
P1 = 10Ohm multiturn preset
P2 = 500Ohm preset H
P3 = 2kOhm 5 preset H
Capacitors:
C1 = 10,000µF 50V (4,700µF 35V), axial
C2 = 470µF 50V, radial
C3,C13,C14,C15,C16,C17 = 10µF 25V, radial
C4,C7,C11 = 100nF, ceramic, 5mm lead pitch
C5 = 10nF, ceramic, 5mm lead pitch
C6 = 1nF, ceramic, 2.5mm lead pitch
C8,C9 = 10µF, tantalum bead
C10 = 4nF7, FKS-2
C12 = 4µ F7 63V, MKS-4
Semiconductors:
D1 = P600D (1N4007)
D2 = zener diode 12V 1.3W
D3,D4,D5,D6 = 1N4148
B1 = B80C5000 (B80C1500)
T1 = BC557B
T2,T3,T4 = TIP142 (1 only)
T5,T6,T7 = BC547B (not fitted)
IC1 = LT1491
IC2 = TLC272
IC3 = PIC16F84A-04P, programmed, order code 000166-42
IC4 = 4066
IC5, IC6 = 74HC164
IC7 = 78L05
IC8 = MAX232
Miscellaneous:
F1 = Fuse, 2A, time lag
F2 = Fuse, 4A, time lag (2A, time lag)
S1-S8 = pushbutton, C&K 3FTL6 + 1S09 22.5, or general-purpose 10x10x20mm, lead pitch 5mm
TR1 = mains transformer, toroid, 24V, 80VA, e.g. UI 39/1721 V, 2571 mA
X1 = ceramic resonator, 4MHz, 3 pins
LCD module 16x1, with backlight
Fuse holder, PCB mount
Fuse holder, chassis mount, (alternatively IEC mains appliance socket with integral fuse)
Two wander sockets (red, black)
Fl1 = mains filter, 2A (not fitted)
K1= 9-way SIL pinheader, with 9-way sub-D socket (female), chassis mount
K2 = 5-way pinheader
K4,K5 = 2-way PCB terminal block, lead pitch 5mm
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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