Transcript Half Wave Rectifier

Power Supplies, Batteries,
Connectors and Test Equipment
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.
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.
Power Supply Specifics
Half Wave – Full Wave Rectifier
Power Supply Specifics
Bridge Rectifier
Rectifier Comparison
Rectifiers – Half Wave
• Rectifiers are semiconductor diodes that conduct in
only one direction. Today, most rectifier diodes are
made of silicon.
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.
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.
Filter Network
Capacitors and inductors are used in
power supply filter networks. The
capacitors and inductors smooth out the
“bumpy” ac to dc.
Electrolytic Capacitor
• Electrolytic capacitors
are used to filter
rectified dc.
• They change “bumpy”
dc to “smooth” dc.
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:
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Easier to filter (just like full wave).
Center-tap transformer not required.
Transformer secondary same as intended voltage.
Higher parts count.
Power Supply Safety
Power Supply Safety
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.
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.
Bleeder Resistors
• A bleeder resistor is installed across the filter
capacitors as a safety feature to make sure that
the capacitors are discharged.
Switching-Mode Power Supplies
Switching Power Supplies
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).
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.
Batteries
• Two basic types:
– Rechargeable.
– Non-rechargeable.
• Rechargeable battery types based on battery
chemistry (NiCd, NiMH, lead acid, etc.).
• Battery chemistry determines:
– Energy rating (ampere-hours).
– Discharge characteristics.
Batteries
• Do not attempt to recharge non-rechargeable
batteries!
• Use only a charger that is designed for the
rechargeable battery in use.
• Follow manufacturer’s specifications for
recharging.
• Dispose of spent batteries properly.
Connectors
PL-259
BNC
Connectors
• DB-25 or DB-9 connectors are for computer cables.
• Amateur/RF connectors include:
 PL-259
 BNC
 N
• A Type N coaxial connector would be a good choice to
use for 10 GHz feed-line connections.
Basic Test Equipment
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VOM
Frequency Standard
SWR Meter
Antenna Analyzer
Oscilloscope
Signal Generator
Noise Bridge
Field Strength Meter
Monitor Scope
Two-Tone Test Generator (for
SSB)
Test Equipment: Volt-Ohm-Meter
VOM
Test Equipment: SWR and Watt Meter
Test Equipment: Oscilloscope
Test Equipment: Oscilloscope
Test Equipment: Noise Bridge
• Connected between a
receiver and an antenna of
unknown impedance and
tuned for minimum noise.
• Can determine characteristic
impedance for transmission
lines.
• Can be used for pre-tuning
an antenna tuner.