Switching Power Supply

One of the main features of the regulated power supply circuit being presented is that though fixed-voltage regulator LM7805 is used in the circuit, its output voltage is variable. This is achieved by connecting a potentiometer between common terminal of regulator IC and ground. For every 100-ohm increment in the in-circuit value of the resistance of potentiometer VR1, the output voltage increases by 1 volt. Thus, the output varies from 3.7V to 8.7V (taking into account 1.3-volt drop across diodes D1 and D2). Another important feature of the supply is that it switches itself off when no load is connected across its output terminals. This is achieved with the help of transistors T1 and T2, diodes D1 and D2, and capacitor C2. When a load is connected at the output, potential drop across diodes D1 and D2 (approximately 1.3V) is sufficient for transistors T2 and T1 to conduct. As a result, the relay gets energised and remains in that state as long as the load remains connected. At the same time, capacitor C2 gets charged to around 7-8 volt potential through transistor T2. But when the load is disconnected, transistor T2 is cut off. However, capacitor C2 is still charged and it starts discharging through base of transistor T1. After some time (which is basically determined by value of C2), relay RL1 is de-energised, which switches off the mains input to primary of transformer X1. To resume the power again, switch S1 should be pressed momentarily. Higher the value of capacitor C2, more will be the delay in switching off the power supply on disconnection of the load, and vice versa.Though in the prototype a transformer with a secondary voltage of 12V-0V, 250mA was used, it can nevertheless be changed as per user’s requirement (up to 30V maximum. and 1-ampere current rating). For drawing more than 300mA current, the regulator IC must be fitted with a small heat sink over a mica insulator. When the transformer’s secondary voltage increases beyond 12 volts (RMS), potentiometer VR1 must be redimensioned. Also, the relay voltage rating should be redetermined.

Power Supplay 13,8 Volt

Build A 10 Amp 13.8 Volt Power Supply
http://dasar-elektonika.blogspot.com
Sometimes amateurs like to home-brew their power supplies instead of purchasing one off the shelf at any of the major ham radio retail dealers. The advantage to rolling your own power supply is that it teaches us how they work and makes it easier to troubleshoot and repair other power supply units in the shack. It should be noted that there is no real cost advantage to building your own power supply unless you can get a large power transformer and heat sink for a super low price. Of course rolling our own gives us the ability to customize the circuit and make it even more reliable than commercial units. The circuit in Figure 1 will give us 10 amps (12 amps surge) with performance that equals or exceeds any commercial unit. The circuit even has a current limiting feature which is a more reliable system than most commercial units have.
Just like other commercial units, this circuit uses the LM723 IC which gives us excellent voltage regulation. The circuit uses 3 pass transistors which must be heat sinked. Resistor R9 allows the fine tuning of the voltage to exactly 13.8 volts and the resistor network formed by resistors R4 through R7 controls the current limiting. The LM723 limits the current when the voltage drop across R5 approaches .7 volts. To reduce costs, most commercial units rely on the HFE of the pass transistors to determine the current limiting. The fault in that system is that the HFE of the pass transistors actually increases when the transistors heat up and risks a thermal runaway condition causing a possible failure of the pass transistors. Because this circuit samples the collector current of the pass transistors, thermal runaway is not a problem in this circuit making it a much more reliable power supply.
The only adjustment required is setting R9 to the desired output voltage of anywhere between 10 and 14 volts. You may use a front panel mounted 1K potentiometer for this purpose if desired. Resistor R1 only enhances temperature stability and can be eliminated if desired by connecting pins 5 and 6 of IC-1 together. Although it really isn't needed due to the type of current limiting circuit used, over voltage protection can be added to the circuit by connecting the circuit of Figure 2 to Vout. The only way over voltage could occur is if transistors Q2 or Q3 were to fail with a collector to emitter short. Although collector to emitter shorts do happen, it is more much more likely that the transistors will open up when they fail. I actually tested this and purposely destroyed several 2N3055's by shorting the emitters to ground. In all cases the transistors opened up and no collector to emitter short occurred in any transistor. In any event, the optional circuit in Figure 2 will give you that extra peace of mind when a very expensive radio is used with the power supply.
The circuit in Figure 2 senses when the voltage exceeds 15 volts and causes the zener diode to conduct. When the zener diode conducts, the gate of the SCR is turned on and causes the SCR to short which blows the 15 amp fuse and shuts off the output voltage. A 2N6399 was used for the SCR in the prototype but any suitable SCR can be used. While over voltage protection is a good idea, it should not be considered a substitute for large heat sinks. I personally feel the best protection from over voltage is the use of large heat sinks and a reliable current limiting circuit. Be sure to use large heat sinks along with heat sink grease for the 2N3055 transistors.
I have used this power supply in my shack for several months on all kinds of transceivers from HF, VHF to UHF with excellent results and absolutely no hum. This power supply will be a welcome addition to your shack and will greatly enhance your knowledge of power supplies.
DE N1HFX
Parts List
R1 = 1.5K ¼ Watt Resistor (optional, tie pins 6 & 5 of IC1 together if not used.)
R2,R3 = 0.1 Ohm 10 Watt Resistor (Tech America 900-1002)
R4 = 270 Ohm ¼ Watt Resistor
R5 = 680 Ohm ¼ Watt Resistor
R6,R7 = 0.15 Ohm 10 Watt Resistor (Tech America 900-1006)
R8 = 2.7K ¼ Watt Resistor
R9 = 1K Trimmer Potentiometer (RS271-280)
R10 = 3.3K ¼ Watt Resistor
C1,C2,C3,C4 = 4700 Microfarad Electrolytic Capacitor 35 Volt (observe polarity)
C5 = 100 Picofarad Ceramic Disk Capacitor
C6 = 1000 Microfarad Electrolytic Capacitor 25 Volt (observe polarity)
IC1 = LM723 (RS276-1740) Voltage Regulator IC. Socket is recommended.
Q1 = TIP3055T (RS276-2020) NPN Transistor (TO-220 Heat Sink Required)
Q2,Q3 = 2N3055 (RS276-2041) NPN Transistor (Large TO-3 Heat Sink Required)
S1 = Any SPST Toggle Switch
F1 = 3 Amp Fast Blow Fuse
D1-D4 = Full Wave Bridge Rectifier (RS276-1185)
T1 = 18 Volt, 10 Amp Transformer Hammond #165S18 (Digi-Key HM538-ND)

There is no thrill like the thrill you get from operating equipment you have built yourself. If you have never built a project from a magazine before, let this be your first--you'll see how much satisfaction and fun you can have!
The FM transmitter is designed run from a 9-volt battery and is made from readily available parts. The author's primary use is as a baby monitor, but uses of a transmitter like this one are almost limitless. It is very sensitive, and easily capable of picking up a conversation in any part of the room. The dimensions and values give here will allow static-free reception within the perimeter of most homes.
No license is required for this transmitter according to FCC regulations regarding wireless microphones. (The emissions must stay within a band of 200 KHz, its output between 88 and 108 MHz, and the field strength of the radiated emissions must not exceed 50uV/m at a distance of 15 meters (45 feet) from the device.)
If powered from a 9-volt battery and used with an antenna no longer than 12 inches, the transmitter's radiated power will be within the FCC limits. The FCC takes a dim view of persons operating outside the legal power limits, so please do not substitute any components in this circuit which would alter the output power.

Parts List:
All resistors are 1/8-watt, 5%.
R1,R6 = 1K C1,C3 = 10uF/25V, electrolytic
R2 = 15K C2 = 2.2uF/25V, electrolytic
R3 = 6K8 C4,C7 = 0.1uF/25V, ceramic
R4 = 10K C5 = 5 to 60pF, trimmer
R5,R7 = 4K7 C6 = hand-made (see text)
R8 = 2K2 Q1,Q2 = 2N2222(A), NPN transistor
R9 = 220 ohms L1 = hand-made (see text)
Miscellaneous: perforated construction board, 9-Volt battery, battery clip,
electret microphone, 24-gauge insulated wire, bare wire, solder.
Circuitry:
Take a look at the schematic above. Audio is picked up from the room by an electret microphone and amplified by Q1. Resistors R2-R5 set up the DC operating bias of Q1. Capacitor C3 serves to improve the AC response to the audio voltage, and C2 blocks the DC bias and couples the AC to the next stage, where the RF action takes place. The amplified AC voltage from Q1 is routed to the base of Q2. Transistor Q2 and associated circuitry (C5 and the inductor) form an oscillator that operates in the 80-130 MHz range, which is your regular dial on any FM radio.
The oscillator is voltage-controlled, so it is modulated by the audio voltage that is applied to the base of Q2. Resistor R6 limits the input to the RF section, and its value can be adjusted as necessary to limit the volume of the input. That will help control the amount of distortion you have on very loud inputs.
Resistors R7-R9 set the DC operating bias of Q2, another 2N2222 that's used as the oscillator and modulator of the transmitter. Capacitor C5 is a 6-50pF trimmer capacitor that's used to tune the oscillator tank circuit, and C4 routes the RF from the oscillator to ground to prevent unstable operation.
Completed Prototype Construction:
The FM transmitter is built on a piece of perforated construction board (a.k.a. 'perf-board') with 0.1-inch hole spacing. Component spacing is not critical, but placement is. You should place the components on the board in a layout that is similar to the prototype shown. Generally, you will also want to make the transmitter as small as possible.
Let's start from the left side of the schematic and work o the tright. You'll want to cut out a piece of perfboard that is 12 holes wide and 30 holes long. That will give you plenty of room to work with, but still produce a small unit. First lay out two power lines on the board with bare wire; the positive supply from the battery will be on top, and the negative (ground) will be on the bottom.
A 1K resistor (R1) supplies the bias voltage for the microphone. Remember to install the resistor vertically, next to the positive supply line, and bend the other end of the lead to the board. Go through the board and down toward the ground bus. Now insert the micophone leads into the board, making sure that the ground lead of the microphone can be soldered to the ground bus on the board. Route the lead from R1 to the positive lead of the microphone and solder it. The 10-uF capacitor, C1, should be placed in the middle of the board, oriented as shown on the schematic, and soldered to the microphone/R1 junction.
This project requires two hand-made parts--coil L1 and capacitor C6--but you make both of them yourself using only wire and a common pencil for the coil form. The inductor ismade by winding two pieces of 24-gauge insulated wire, laid side-by-side, around the pencil six times. Remove the coil you have formed and unscrew the two coils apart from each other. One of these coils, the better-looking of the two, will be used in the tank circuit (L1) and the other can be used in the next one you build.
The other hand-made component, capacitor C6, is part of the oscillator feedback. To make this small value capacitor, take a 4-inch piece of 24-gauge insulated wire, bend it over double and, beginning 1/2-inch from the open end, twist the wire as if you were forming a rope. When you have about 1 inch of twisted wire, stop and cut the looped end off leaving about 1/2-inch of twisted wire (this forms the capacitor) and 1/2-inch of untwisted wire for leads.
Capacitor C7, a 0.1uF capacitor, is one of the most critical components in the circuit. You must place it across the L1-Q2-R9 assembly, as shown in Fig. 1, to reduce the amout of RF feedback you'll get iinto the rest of the circuit. The antenna (more 24-gauge wire) shoucl be soldered to the coil you made, about 2-turns up from the bottom, or the transistor side, and should be about 8-12-inches long.
Operation:
To use the transmitter, set up a radio in the area at least 10 feet (3 meters) from the project. Find a blank spot on the FM dial and turn the radio up so you can hear the static.
Connect a 9-volt battery to the transmitter and listed to the radio. Slowly adjust the tank capacitor (C5) until you "quiet" the receiver; this is the tuned spot. Note that when you move your hand from the transmitter, you will detune the circuit somewhat. It is usually best to leave it detuned and tune the radio in to get the best reception. If you et the tuning randge you desire, you can squeeze the coils in the tank circuit closer together to raise the frequency, or pull them apart just a little to lower it.
The circuit works best when powered by a battery, but if a wall adapter is required, make certain that the ripple voltage is as low as possible, or you will get hum in the receiver. R-E

FM Transmitter (up to 500 meter range)

Parts List:
Resistors are 1/4 Watt, 5%
R1 = 10K
R2 = 86K
R3 = 3K3 (3.3K)
R4 = 2K2
R5 = 100 ohm
Capacitors:
C1,C8 = 2N2 (2.2nF), ceramic
C2 = 4N7, ceramic
C3,C6 = 10pF miniature variable
C4,C9 = 100pF, ceramic
C5 = 1uF, 25V, electrolytic
C7 = 1uF, polyester
Semiconductors:
Q1 = BC108, NTE123A, NPN transistor
Q2 = 2N2369, 2N2222, NTE123A, NPN transistor
Notes:
Q1 and Q2 both reference to a NTE123A replacement type.
With a short antenna the maximum distance is about 600 feet (200M). But with a proper antenna this distance can easily
be changed to about 1/2 mile (800M)! Even so, keep in mind that this simple transmitter is just that; simple!
If you find that the frequency drift a little, secure the coil with candle wax or a dab of hot-melt glue. The coil, L1,
is wound on a 10mm body. Use a wooden dowel or similar. Wind about 4 turn of enameled copper wire
(also called 'magnet wire'). Obviously, remove the body after winding. Scrape the enamel off both ends of the coil
before attempting to solder.
As for the ceramic capacitors, try to find and use the socalled 'NP0' types for low noise/temperature drift. They
have a black stripe at the top of the cap. They are manufactured by Philips.
The variable capacitors, C3 and C6, are just the regular trimmer caps.
This type of transmitter works best in a metal enclosure. Just make sure nothing of your circuit is touching it.
"Gnd." in the schematic diagram just refers to the negative pole of your battery.

4 Transisitor Transmiter

Parts List:
All resistors are 1/4 watt 5%
R1,R2,R8 = 1K C1 = 1uF/63V, electrolytic
R3 = 100K C2,C3 = 10nF, ceramic
R4 = 150K C4,C5,C9 = 4.7uF/63V, electrolytic
R5,R7 = 10K C6,C12,C13,C14 = 1nF, ceramic
R6 = 220 ohm C7,C8,C11 = 5pF, ceramic
R9 = 10 ohm C10 = 220uF/63V, electrolytic
P1 = 5K trimpot
Q1,Q2 = 2N3904 L1 = 3.9uH
Q3,Q4 = 7001, NTE123AP L2 = 1uH
D1 = 1N4002 L3 = aircoil, 8.5 turns air space
1/4 inch diameter
Circuit Notes:
This circuit provides an FM modulated signal with an output power of around 500mW. The input microphone pre-amp is built around a couple of 2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset trim potentiometer.
The oscillator is a Colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor.
(Click here for Colpitts Oscillator Resonant Frequency Equation.)
Frequency is around 100Mhz with values shown.
Audio modulation is fed into the tank circuit via the 5p capacitor, the 10k resistor and 1N4002 controlling the amount of modulation. The oscillator output is fed into the 3.9uH inductor (L1) which will have a high impedance at RF frequencies.
The output stage operates as a 'Class D' amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.

Miniature FM Transmiter 2N2222

Parts List:
R1,R3 = 100K
R2 = 10K
R4 = 470 ohm
C1,C4 = 470pF
C2,C3 = 4.7µF, 16V, electrolytic
C5,C6 = 4.7pF
C7 = 4-40pF trimmer cap (optional, see text)
L1 = 1µH
Q1,Q2 = 2N2222, NPN transistor
Mic = Electret Microphone
B1 = 9 Volt, Alkaline battery
Notes:
Nothing critical here. To get a bit of tuning out of the coil you could put a 4-40pF trimmer capacitor (optional) parallel over the 1 µH coil, L1.
C1/C4 and C5/C6 are ceramic capacitors, preferably NPO (low noise) types. C2/C3 are electrolytic or can be tantalum types.
If you decide to substitute transistors with something similar you already have, it maybe necessary adjust the collector voltage of Q1 by changing the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). It should be about 1/2 the supply voltage (about 4 or 5v).
The antenna is nothing more than a piece of 12" wire or a piece of piano wire from 6" to 12".
To find the signal on your standard FM Radio dial, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver. Most of all...BE PATIENT!

Sensitive FM Transmiter

Parts List:
R1,R3 = 10K C1,C2 = 0.1uF Q1,Q2 = 2N3904
R2 = 100K C3 = 0.001uF L1 = see text
R4 = 4.7K C4 = 10-40pF
R5 = 330 ohm C5 = 4.7pF
Construction:
L1 is 0.1uH, 6 to 8 turns of 22-gauge hookup wire close wound around a 1/4-inch diameter non-conductive core such as a pencil.
The default for the capacitors type is ceramic, preferably the npo 1% type or equivalent. But basically nothing critical here. Use any capacitor you have laying around, but no electrolytic or tantalum caps. Only if you intend to use this circuit outside the home you may want to select more temperature stable capacitors like polyester types. Again, don't go out of your way to buy stuff, use what ever you can salvage.
If you decide to substitute transistors with something similar you already have, it maybe necessary adjust the collector voltage of Q1 by changing the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). It should be about 1/2 the supply voltage (about 4 or 5v).
To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.