The document discusses power supplies, which take alternating current (AC) and convert it to direct current (DC) to power electronic devices. Power supplies consist of a transformer, rectifier, filter network, voltage regulator, and protection components. The document compares different types of rectifiers like half-wave, full-wave, and bridge rectifiers. It also discusses important concepts, safety considerations, and switching mode power supplies.

1. Presentation on
power supplies
Prince kumar kushwaha
0902EC101053

2. Power Supplies
• Power supplies provide
the necessary power,
voltage and current
requirements for
electronic devices.
• They usually change ac
to dc voltage.
– For example, 120 volts
ac is changed to 13.8
volts dc.

3. Power Supplies
Consist of:
1. Transformer – steps ac voltage up or down.
2. Rectifier Diodes – change ac to “bumpy” dc.
3. Filter Network – includes capacitors and
inductors, smooths out the bumps.
4. Voltage Regulator – keeps the voltage constant.
5. Protection – usually a crowbar circuit.

4. Power Supply Specifics
Half Wave – Full Wave Rectifier

5. Power Supply Specifics
Bridge Rectifier

6. Rectifier
Comparison

7. Rectifiers – Half Wave
• Rectifiers are semiconductor diodes that conduct in
only one direction. Today, most rectifier diodes are
made of silicon.

8. Diode Ratings
• Increase current capacity by
putting additional diodes in
parallel.
• Increase voltage capacity by
putting additional diodes in
series.
• Voltage rating 1.4 RMS minimum.

9. Power Supply Filters
• Use large coils (called chokes) and capacitors to
“fill in” the gaps between ripples in the incoming
pulsating dc.
• AC “hum” results from improper filtering.
– Pulling too much current from power supply.
– Failed component (particularly capacitor).
• “Wall-Warts” generally do not produce quality dc.
– Generally produce pulsating dc to charge
batteries.

10. Filter Network
Capacitors and inductors are used in
power supply filter networks. The
capacitors and inductors smooth out
the “bumpy” ac to dc.

11. Important Concepts
• Half Wave Rectifier:
– Simplest.
– Hard to filter well.
• Full Wave Rectifier:
– Easier to filter.
– Requires transformer with center-tap.
– Transformer secondary must be twice intended voltage.
• Bridge Rectifier:
– Easier to filter (just like full wave).
– Center-tap transformer not required.
– Transformer secondary same as intended voltage.
– Higher parts count.

12. Power Supply Safety

13. Power Supply Safety

14. Power Supply Safety
• Grounding is important.
• Connection integrity is important.
– Somewhere neutral and ground are
connected together.
• Miss-wired “hot” lead will lead to a hot
chassis someplace.

15. Power Supply Safety
• Filter capacitors hold a charge a long time.
• They charge to the output voltage of the
power supply.
• Bleeder resistors across the filter
capacitors “bleed off” charge when supply
is turned off.

16. Bleeder Resistors
• A bleeder resistor is installed across the filter
capacitors as a safety feature to make sure
that the capacitors are discharged.

17. Switching-Mode Power Supplies

18. Switching Power Supplies

19. Switching Power Supplies
• The advantage of a switching-mode power supply is
that the relatively high frequency oscillator allows
the use of small, lightweight and low-cost
transformers.
• This makes them considerably smaller and lighter
than linear power supplies. Almost all modern
powers supplies, including those in PCs, are
switching mode power supplies. Their
disadvantages are complexity and RF egress
(interference).

20. Switching Power Supplies
In a switched mode power supply, the first step
in converting 120 V ac to a 12 V dc output is to
rectify and filter the 120 V.