1. Linear Power Supplies, Switched Mode Power Supply
Unit 7
Linear Power Supplies, Switched Mode Power Supply

2. Learning Objectives: Linear Power Supplies:
14.1 Constituents of Linear Power Supply
14.2 Designing Mains Transformer
14.6 Linear IC Voltage Regulators
14.7 Regulated Power Supply Parameters
Switched Mode Power Supplies:
15.1 Switched Mode Power Supplies
15.6 Connecting Power Converters in Series
15.7 Connecting Power Converters in Parallel

3. 14.1 Constituents Linear Power Supply:
Stepdown transformer
Rectifier
Filter (C, LC)
Regulator (ICs LM78XX, LM79XX, LM321)

4. 14.2 Designing Mains Transformer:
To avoid magnetic saturation – core cross section area, Ac
Ac = √P / 5.6
where P=power required in Watts
t / W ratio =
stack thickness (t)
= 1.1 to 1.5
Width of central limb (W)

5. … Turns per volt = Where f=frequency=50 or 60 Hz
108
4.44 x f x Ac x B
Where
f=frequency=50 or 60 Hz
B=flux density=50000 lines / square inch (gauss)

6. ------------------------------------- Efficiency x Primary Voltage
Turns ratio (Ns / Np), n
=Vp / Vs = Ns / Np
Primary current = P
Efficiency x Primary Voltage

7. … Secondary current = Primary Current ----------------------- n
where n is turns ratio

8. 14.1 Numerical Example:

10. 14.6 Linear IC Regulators: Features: PCB mountable Precision
Best voltage & current regulation
Wide range of output voltages
Protection inbuilt: current limit & thermal shutdown

13. Three terminal regulators:

14. Boosting current delivery capability:

15. 14.7 Regulated Power Supply Para meters:
Load regulation:
Change in regulated output voltage as the load current varies.
VNL – VFL
% load regulation = X 100
VFL

16. Line regulation:
is defined in terms of variation of regulated output voltage for a specified change in line (input AC) voltage.
Eg.
For input voltage variation, say 170 V to 220V, output voltage 10V, varies ±1% has line-regulation (1+1)
= x 100 10
= 0.2 %

17. Output Impedance:
In Thevenin’s equivalent circuit of RPS, output impedance comes in series with load resistance.
It determines load regulation of the power supply.

18. Ripple rejection factor:

21. 15.1 Switched Mode Power Supplies:
power supply
Linear Switched
Stepped down,
Rectified,
Filtered,
Regulated
Loss
Costly
The unregulated DC is chopped at a
high frequency (using transistor /
MOSFET / IGBT)
The chopped waveform is then rectified
and filtered to get the desired DC voltage.

22. 15.5 Switching Regulator: Buck regulator – step down
Boost regulator – step up
Buck-boost regulator – both step down / up

23. 15.6 Connecting Power Converters in Series:
Can be connected in series, provided specifications allow for the series connections.
It is possible that the output of one converter affects the output loop of another.
Output voltage should not exceed breakdown voltage of the devices.

25. 15.6 Connecting Power Converters in parallel:
Again, if specification allow the connection, then they can be connected in parallel.