DC power supplies work by taking an AC voltage from a transformer, rectifying it using diodes to convert it to DC, filtering it using capacitors to smooth the output, and regulating it using integrated circuits to maintain a steady voltage level. Common rectification methods include half-wave and full-wave rectification using either single-phase or three-phase inputs. The rectification process converts the AC voltage to a pulsing DC voltage that is then filtered and regulated.

1. DC POWER
SUPPLIES

2. Block diagram
DC power supply
Transformer Rectifier Filter Regulator
D
C
Revision 01 2

3. Rectification
Rectification is the process by which
an alternating voltage or current is
changed to a unidirectional (one way)
voltage or current.

4. The AC Sinewave
Peak voltage = √2 x V rms = 1.414 x V rms

5. An AC voltage is defined as a voltage that periodically reverses
polarity and will cause current to flow in the reverse direction.
A DC voltage is a voltage that does not reverse direction, and
causes current to flow in one direction only.
When an AC voltage is measured with a voltmeter, the indicated
value will be the RMS value
(V rms = 0.707 x V peak) or (V rms = V peak) of the waveform)
√2
When a DC voltage is measured, the meter will indicate the
average of the DC voltage waveform.

6. Single phase half wave
AC Supply
Load
+
+
-
TIME -
TIME
Revision 01 6

7. Half Wave Single Phase Rectification
V load = V average = 0.318 x V peak or 0 .45 x V rms
fr = fs
PIV = √ 2 x V rms
V ripple = √ 2 x V rms

8. Center tapped full wave
Load
AC Supply
+
-
TIME +
-
TIME
Revision 01 8

9. Full Wave Single Phase
Rectification
V load = V average = 0.638 x V peak or 0 .9 x V rms
fr = 2 x fs
PIV = √ 2 x V rms (bridge rectifier)
PIV = √ 2 x (2 x V rms) (centre tapped rectifier)
V ripple = √ 2 x V rms

10. Single phase bridge rectifier
+
AC Supply -
D D2 TIME
+ 1
- D3 D4
TIME
Load
Revision 01 10

11. Printed circuit board
Cables Tracks - DC Supply
AC Supply
DC terminals
AC
terminal
s
Revision 01 11

12. Remember
V Line = √3 x V phase

13. V Line V Phase
Revision 01 13

14. Three phase half wave
D
1
3 Phase Supply Load
D2
D3
+ +
- - TIM
E
TIME
Revision 01 14

15. Half Wave Three Phase
Rectification
V load = V average = 0.827 x V peak or 1.17 x V rms
fr = 3 x fs
PIV =2.45 x V phase rms (√ 2 x√ 3 x V rms)
V ripple = 0.707 x V rms

16. Three phase full wave
Suppl
y
D D3
D2
1
+
- TIM
E
D4 D5 D
6
+
-
TIME
Revision 01 16

17. Full Wave Three Phase
Rectification
V load = V average = 0.955 x V peak or
1.34 x V line rms or 2.34 x V phase rms
fr = 6 x fs
PIV =√ 2 x V line rms
V ripple = 0.16 x V rms