D:\Edtech 2\Day5 Lesson11 N0ss

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 SpecificsHalf Wave Rectifier

Power Supply SpecificsFull Wave Center-Tapped Rectifier

Power Supply SpecificsFull Wave 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, or by using a diode with a larger contact surface area.

• Increase voltage capacity by putting additional diodes in series, or by using a diode manufactured with a higher voltage rating.

• Use a diode with a voltage rating of at least 1.4 times the RMS voltage, 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).

• Plug-in-the-wall power supplies (Wall-Warts) generally do not produce high quality DC. They may work for some low-current applications however.

– Wall-Warts generally produce pulsating DC, suitable for charge batteries, and running some small devices.

Filter NetworkCapacitors are used in power supply filter networks. The capacitors smooth out the “bumpy” AC to DC.

Filter NetworkCapacitors AND Inductors are used in power supply filter networks. The inductors aide the capacitors to smooth out the “bumpy” DC.

Electrolytic Capacitor Electrolytic capacitors

are used to filter rectified DC.

•They change “bumpy” DC to “smooth(er)” DC.

Important Concepts• Half Wave Rectifier:

– Simplest.– Hard to filter well.

• Full Wave Center-Tapped Rectifier:– Easier to filter.– Requires transformer with center-tap.– Transformer secondary must be twice intended voltage.

• Full Wave Bridge Rectifier:– 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 SupplyFilter Capacitor Safety

• They are charged up to the output voltage of the power supply while it’s in operation.

• Filter capacitors hold a charge a long time.

• 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 (50kHz- 150kHz) oscillator allows the use of small, lightweight and low-cost transformers.

This makes them considerably smaller and lighter than linear power supplies. Many ‘modern’ powers supplies, including those in PCs, are switching mode power supplies. Their disadvantages are circuit complexity and their potential for radiation of RF interference (at harmonics of the oscillator frequency), throughout the RF spectrum, to other devices.

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 Batteries can often be used to provide power for your

radio equipment when it is inconvenient to try to power the equipment from the electrical power mains.

In many cases high-capacity batteries can be fabricated to allow “portable power’ to be built into your radio. But in some instances, the radio may require more power then a small “portable” battery can provide. That’s when a ‘storage battery’ can come in handy.

All batteries require additional ‘attention’ from the user and must be ‘maintained’ to in order to provide useful service.

Batteries Two basic types (based upon their ‘chemistry’):

Non-Rechargeable: Carbon-Zinc, Alkaline, Lithium Rechargeable: NiCd, NiMH, LiIon, lead acid, etc.

Battery chemistry determines: Energy rating (ampere-hours), how much power

they can provide over their single-charge ‘useful life’.

Discharge characteristics, how long they can provide useful power during a single-use event.

Battery Handling/Safety Tips Do not attempt to recharge non-rechargeable

batteries! Use only a charger that is designed for that particular

type of rechargeable battery. Using the wrong charger can damage the battery, and can cause damage to the user and his home.

Follow the manufacturer’s specifications for recharging. LiIon cells are particularly ‘touchy’ (can explode) if not properly charged.

Dispose of spent batteries properly.

• 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.

Connectors•DB-25 or DB-9 connectors are for computer cables.

Basic Test Equipment• VOM (Volt-Ohmmeter), or

DMM (Digital Multimeter)• SWR Meter / Wattmeter• Antenna Analyzer• Monitor Scope• Oscilloscope• Signal Generator• Noise Bridge• Field Strength Meter• Frequency Standard• Two-Tone Test Generator (for

SSB)

Test Equipment:V-O-M (Analog Multi-Meter)

A Volt-Ohm Meter, incorporating an analog meter which the user must ‘read’ in order to obtain useful information fro the meter. Measurement ‘range’ and metering ‘mode’ selection is provided by a rotary switch. Accuracy is often +/-10% of the meter reading, not including the user’s ability to ‘read’ the meter itself. A handy tool for the Amateur.

Test Equipment:DMM (Digital Multi-Meter)

In use, not significantly different from the analog V-O-M, other than the fact that the readout is numeric and tends to possibly ‘imply’ a higher accuracy than the meter may be able to provide. Users tend to ‘trust’ the implied high-accuracy of a digital readout more than they trust an analog meter when they have to read and interpret the needle position. Also a handy tool in the shack.

The difference between the accuracy of a V-O-M (+/- 5% to 10%), when compared to that of a DMM (usually +/-0.1% to 1%) may or may not be of much importance to the user. When using a meter, many times the importance of the reading is not the absolute accuracy, but the difference between toe readings taken with the same meter. It may be much more important to know whether reading #2 was higher (or lower) than reading #1, than to know whether the reading is within 1% of the intended value. So, while a DMM may give more accurate readings, the V-O-M may provide just as usable measurements under certain circumstances.

V-O-M vs. DMM Accuracy

Test Equipment: SWR and Watt Meter

These devices allow you to keep track of the degree of ‘match’ between your transmitter (50 Ohm) output and that of the antenna/feedline ‘load’ being provided to the transmitter. They also allow you to monitor your transmitter output power.

Test Equipment: Antenna SWR Analyzer

This device incorporates thefeatures of a very low-powertransmitter and an SWR meterinto a single, portable, devicewhich can be used to obtainimportant information aboutthe antenna to which it is attached.It allows you to ‘tune’ the antennawithout transmitting signals harmful to communications on the same frequency.

Test Equipment: Station Monitor ScopeThe station Monitor scope allows you to ‘see’ your transmitted signal in real-time. It is installed in the transmission line so it can actually ‘look’ directly at your signal as you transmit. So if there is a problem with the signal, you can see the indication and take steps to fix it before it becomes a problem for others. The image below, illustrates a single MorseCode DIT (dot) which has been ‘stopped’ on-screen for the operator to examine

Test Equipment: Station Monitor ScopeSample Monitor Scope RF Envelope Waveforms

Continuous Carrier InputNo RF Signal Input

Morse Single DIT SSB Voice SIgnal

Test Equipment: OscilloscopeOscilloscopes arespecialty test deviceswhich can be of useto the radio amateurin certain instances.They allow you to ‘look’ at signals ofall kinds and to use what you see for analytical purposes.‘Scopes can be costly, but can be worth the investment ifyou have a real use for them. They are NOT specifically ‘required’ for the normal ham’s shack however.

Test Equipment: OscilloscopeUsing an oscilloscope to compare the values of two different signal inputs (red and lt. blue, below).

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.