§ 2.4 - Single Positive Power Supply, Regulated
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Before you attempt this build, please:
- Read through the numbered build procedure with the idea of performing the listed steps in order
Examine the PCB layout
Examine the schematic diagram
Refer to each of the linked pages in the "See also" list
This will help ensure that you will have the best possible experience, resulting in a build that works the way you expect it to.
Schottky diodes are recommended; these diodes have a much lower forward voltage drop, and so will waste less power and run cooler under load.
Optional: Install test points — Important: If these are used, they must be first components installed!
D2 — at least a PIV equal to the total secondary voltage of T1, 2 amps or more. Observe polarity.
D4 — at least a PIV equal to the total secondary voltage of T1, 2 amps or more. Observe polarity.
D5 — steering diode — at least a PIV equal to the total secondary voltage of T1, 2 amps or more. Observe polarity.
R1 — calculate the ohms and watts values for R1 here.
C1 — ceramic .22 uF — equal to or higher than the total secondary voltage voltage of T1
C3 — ceramic .1 uF — equal to or higher than the total secondary voltage voltage of T1
C5 — Polarized electrolytic — Calculate the uF and WV value of C5 here. Observe polarity.
IC1 — 78xx-series three-terminal positive voltage regulator. Observe polarity. See Heatsink Considerations. Consider off-board mounting.
LED1 — a low-power LED of whatever color you prefer. Observe polarity.
T1 — Center-tapped-winding secondary power transformer (see Choosing a Transformer)
If battery backup is used, the battery backup input voltage must be less
than the minimum ripple voltage plus the steering diode drop
volts for Si diodes, .25
volts for Schottky diodes) of the loaded power supply. You can use the filter capacitor calculator
to ensure that the minimum ripple voltage is above
the battery input voltage minus the steering diode drop
. If the battery voltage minus the steering diode drop is above the minimum ripple voltage, the battery will discharge continuously until it falls below this level, which will usually mean the battery can no longer function as a backup power source.
The footprints for filter capacitors C
5 and C
6 are designed to accommodate many different capacitor sizes and lead spacings. Each of the four-hole "diamonds" is one connection; you can use any one of the four diamond through-holes to connect one lead of your capacitor(s.)
Carefully observe polarity
as shown in the layout diagram below and connect each lead of your filter capacitors into the correct diamond.
Positive Power Supply, Regulated, Build Guide
All components match PCB silkscreen
+ build regulator placement
Output Connection Detail
Plus regulated build schematic
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