11.04.2014

Dc transformer for led

Amateur radio has been somewhat slow to accept switching power supplies for powering communication equipment.
Some early switchers produced an objectionable amount of RF noise, bringing the whole switching technology into bad reputation.
In this article I will describe the construction of a switching power supply designed to power a complete ham station, with several radios and accessories. Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors.
1Hz - 2MHz XR2206 Function Generator produces high quality sine, square and triangle waveforms of high-stability and accuracy. Having the ability to control various appliances inside or outside of your house wirelessly is a huge convenience, and can make your life much easier and fun. If you require further details regarding the transaction data, please contact the supplier directly. This is a pity, because "switchers", as they are often called, offer very attractive features, like small size, low weight, high efficiency, and low heating. But by proper design techniques and careful EMI filtering it is possible to build very quiet switchers. This power supply produces 13.8V regulated to better than 1%, at a continuous load current of up to 40A. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors.
The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored.
It is a very useful bench test equipment for testing and finding out the frequency of various devices with unknown frequency such as oscillators, radio receivers, transmitters, function generators, crystals, etc. BA1404 HI-FI Stereo FM Transmitter broadcasts high quality stereo signal in 88MHz - 108MHz FM band. It is an irreplaceable tool for troubleshooting and repairing electronic equipment by determining performance and health of electrolytic capacitors.
8-DIP machined IC socket allows to swap OPA2134 with many other dual opamp chips such as OPA2132, OPA2227, OPA2228, dual OPA132, OPA627, etc.
It's breadboard compatible so it can be plugged into a breadboard for quick prototyping, and it has VCC & GND power pins available on both sides of PCB.
True, they are generally more complicated than linear power supplies, but this is easily compensated by the fact that they can be built for a lower cost.
It has current limiting, making it appropriate for direct connection to a 12V backup battery.
It can be connected to any type of stereo audio source such as iPod, Computer, Laptop, CD Player, Walkman, Television, Satellite Receiver, Tape Deck or other stereo system to transmit stereo sound with excellent clarity throughout your home, office, yard or camp ground. Unlike other ESR Meters that only measure ESR value this one measures capacitor's ESR value as well as its capacitance all at the same time. Headphone amplifier is small enough to fit in Altoids tin box, and thanks to low power consumption may be supplied from a single 9V battery.
It's small, power efficient, yet customizable through onboard 2 x 7 perfboard that can be used for connecting various sensors and connectors.
You can control lights, fans, AC system, computer, printer, amplifier, robots, garage door, security systems, motor-driven curtains, motorized window blinds, door locks, sprinklers, motorized projection screens and anything else you can think of. If the current limit potentiometer is turned up, the power supply can deliver up to 60A on an intermittent basis, while maintaining regulation. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings. Arduino Prototype uses all standard through-hole components for easy construction, two of which are hidden underneath IC socket. USB IO Board is self-powered by USB port and can provide up to 500mA for electronic projects. Board features 28-PIN DIP IC socket, user replaceable ATmega328 microcontroller flashed with Arduino bootloader, 16MHz crystal resonator and a reset switch.
One end of the winding is usually connected in common to both the voltage source and the electrical load.
A cooling fan operates depending on the average current drawn, and a tricolor LED tells you if the voltage is normal, too high or too low.
Arduino sketches are uploaded through any USB-Serial adapter connected to 6-PIN ICSP female header. Board is supplied by 2-5V voltage and may be powered by a battery such as Lithium Ion cell, two AA cells, external power supply or USB power adapter. And you get all this in a box that measures just 306 x 150 x 130mm, including all projections, and weighs only 2.8kg! Interested?
The calibrated dial reads approximately the output voltage at no-load, when the input is at its rated value. Similarly, three 240-volt units are ganged in a star connection to result in a 470-volt line-to-line three-phase assembly. For 480-volt open delta applications, two 240-volt units are used in series in each of the two legs of the open delta assembly. The AC input is heavily filtered, first by the filter inside the CEE-22 connector, which is effective against both common mode and differential mode noise, and then by C1-L1-C2, which forms an additional common mode filter.
Between C3 and the power oscillator two ferrite beads perform a critical noise absorbing task.
These are Amidon beads, made from 73-type material, which unlike most ferrites has good absorption characteristics even in the lower HF range. On the output side, L2 already absorbs most of the noise.


It is wound on a high permeability iron powder toroid, which is very lossy in the HF range. This not only reduces the ripple on the output, but also improves their usefulness as noise filters. L3 is another noise absorber.
To minimize capacitive coupling over it, I wound it on a ferrite solenoid instead of a toroid, so the input windings are far apart from the output ones. The ferrite used is of the type that starts absorbing at HF, so this coil like the others not only blocks, but also absorbs RF energy. It should be noted here that the ground on the printed circuit board is floating, but the enclosure is connected to earth. This arrangement reduces HF current flow on the enclosure, which would lead the box to act as a noise radiator instead of a shield! For some of the more specific devices, RS stock numbers are given. Please do not ask me to get the parts for you.
I'm glad to give you any advise and help needed to complete this project, but I do not provide parts for it. Winding the transformers and coils First things first. Let's start with T1, the main power transformer, which can be considered the heart of this circuit. I built T1 using a tape winding technique, and stacking four pairs of ferrite E cores to get the necessary magnetic capabilities. If you prefer and have enough knowledge, of course you can go your own route. Because four cores are stacked, there is no factory-made bobbin available for this transformer.
I wound the transformer using copper strips interleaved with Mylar sheet, because the thick wire necessary for the heavy current would be impossible to bend around the sharp corners of the bobbin. Instead of using a lot of thin wires in parallel, it is better to take this in a consequent manner and use copper tape.
As the center legs of the four stacked cores measure 62 x 12mm, this wood block must be 63mm wide and 12.5mm thick, to allow for some playroom. The height of the bobbin will be 28mm, so give theblock enough length to hold it with the bobbin in place.
If you have a low speed lathe, winding machine, or similar, cut the wood block to such a length that you can mount it in the machine.
If the block is too big, you will be wasting valuablewinding space, running the risk of not being able to fit the windings. And if the block comes out too small, your finished winding assembly may not fit the ferrite cores, making it unusable. Now wrap the wood block in one layer of plastic film, of the kind used in the kitchen to preserve food.
Mix some 5-minute epoxy glue (I used the type sold in airplane modelling shops, which comes in good sized bottles), and apply a layer of epoxy to the paper strip. Now wind the strip very tightly around the plastic-wrapped wood block, to make the bobbin core. Wrap another sheet of plastic film around your work, and press it between two wooden blocks hold together with rubber bands, so the long sides of the bobbin become flat and nice. Now get permission from your wife, mother, or whoever reigns in the kitchen, and place the assembly in the oven for about 15 minutes at 50oC. If you can make long strips, say 2m, this is an advantage, otherwise you will have to solder individual copper strips together. In total, you will need about 7m of copper tape and slightly less Mylar tape. When you are ready with this, your epoxy has had ample time to harden, so rescue your bobbin from the oven and go on. Take off the rubber bands, the outer wood blocks, and the outer plastic wrapping (don't worry if it doesn't come off completely). You now have your wrapped wooden core and the epoxy-paper bobbin on it. Take a 60mm piece of #13 bare copper wire.
Wrap the end of one of your copper strips around the wire, so that the wire protrudes only to one side from the copper sheet loop. Try to avoid getting solder on the outside, because this may later puncture through the Mylar insulation. Now the winding starts.
Position the copper wire on one narrow side of the bobbin, so that the copper strip is centered on the width of the bobbin, leaving 3mm room on each side. Position the start of one piece of Mylar strip so that it covers all the copper and is centered on the bobbin, and tape it in place. Now wind 15 turns of this copper-Mylar sandwich, as tightly as you can, keeping the Mylar aligned with the bobbin sides, and the copper nicely centered.
If your copper strip is not long enough, fix everything with rubber bands or a clamp, and solder another copper strip to the end of the short one, allowing 2mm of overlap.
Before doing this, cut the first copper sheet to a length such that the joint will be on one of the narrow sides of the bobbin, because here you have space, while the wide sides will have to fit inside the ferrite core's window. But it's only four turns total, so take a deep breath and do it! First solder the four copper strips together around a piece of #13 copper wire. Don't be overly worried if the outcome is not very clean; mine was quite a mess too, and it worked well on the first try. Just be sure you don't create sharp edges or pointed solder mounds, because these may damage the insulation. Now position the start of your secondary conductor in such a way that the pin will come out to the same side as those of the primary, but on the other narrow side of the coil assembly. So you will get a transformer that has its primary leads on one extreme and the secondary on the other, and will fit the printed circuit board nicely. Wind two turns, solder the center tap wire between the four copper strips, wind the other two turns, solder the last pin, wind a finishing layer of Mylar and fix it in place with adhesive tape.
This completes the manufacture of T1. All the other transformers and coils are just child's play after making T1.
The current sense transformer T2 has a lot of turns, but there is absolutely no need to wind them nicely side-by-side.
Get some #36 or other thin enameled wire, solder the end of it to one of the extreme pins of the EE24-25-B bobbin, and wind 100 turns.


Don't worry if your winding is criss-cross and ugly, and don't feel guilty if you loose count and wind a few turns more or less. As long as you don't overdo it, it will just affect the position of VR1 when you align the completed power supply later. Solder the wire tothe center pin of the same side, then wind another 100 turns in the same sense.
Solder to the other extreme pin on the same bobbin side, and apply one or two layers of Mylar, just to protect the thin wire. Now take a piece of #15 plastic insulated cable, wind one single turn over the Mylar and solder the two ends of the cable to the two extreme pins of the other side of the bobbin. Install the EA77-250 core with a small amount of epoxy cement, and T2 is ready. T3 is made using the same type of bobbin and core as T2.
Bring the wires out to one side of the bobbin in such a way that they will not be too close to the other windings. This will leave a space at one side of the bobbin which is big enough to take the single turn of #15 plastic insulated cable, which completes the assembly. Now glue the core in place with epoxy cement, and T3 is ready! L2 is wound on an Amidon T-157-26 iron powder toroid core. As it is too difficult to bend thick wire through a toroid, and tape winding it is not practical either, I chose to make this coil with 10 pieces of #16 enameled wire in parallel. Then insert the bundle into the core, and starting from the middle of the wire bundle, wind 7 turns, using half of the core's circumference.
Now wind the other 7 turns, starting from the middle towards the other end of the wire bundle. The tinned pins can be soldered easily and safely, but even in gold-plated sockets those tin-plated pins oxidize, insulating themselves. They are screwed to the fan, the PCB, and to a 120mm long spreader tube of 6mm diameter, so that these parts become integral to the structure.
The connections between the PCB, aluminum plates and fan are made with small pieces of 10 x 10mm aluminum angle stock. The assembly is surprisingly rigid! The top and bottom covers are made from 1mm aluminum sheet and measure 126 x 300mm.
The bottom cover has a hole for taking the center mount of the PCB.The side covers are cut from wire mesh to allow unrestricted air flow, and measure 122 x 126mm. The panels are held together by 10 x 10mm aluminum angle stock, which runs along all edges, and by small sheet metal screws.
But these covers are not installed until the power supply is complete, tested and adjusted. I painted all the panels flat black on the outside, which looks nice together with the anodized aluminum angle stock. But I kept the edges and insides free of paint, in order to get proper electrical contact between the panels, and shielding action. The components that are external to the PCB (P1, SW1, C3, the LED, and the output screw block) are mounted to the front and rear panels.
Q1 and Q2 are screwed to the rear panel, using M3 nylon screws and 3mm thick ceramic insulators.
These thick insulators were used not only for safety reasons, but mainly because they reduce the capacitive coupling of the transistors to the enclosure. This is very important, because if the unwanted capacities at this place were significant, the switching spikes would be coupled to the enclosure, causing RF current to flow on it and noise to be radiated! It is of little use to filter the input and output leads, if you make your shield radiate the noise by using too thin insulators for the noise-generating transistors! Do not use metal screws with plastic washers, because this approach does not give enough safety margin to operate at line voltage. If you dislike nylon screws, a good alternative are steel clamps that press onto the plastic body of the transistors. The Schottky diodes are mounted using the same kind of insulators and screws, but there is a heat spreader, made from 6mm aluminum plate, between those insulators and the case. All surfaces requiring thermal contact are covered with heat transfer compound before assembly. When installing the diodes and transistors, first do all the mechanical assembly, then solder the pins. Now take your big and very hot soldering iron, and flow generous amounts of solder onto all of those tracks, so that the reinforcing wire becomes buried in the solder. At the end, you will have tracks in which the copper wire does most of the conduction, while the solder couples the generated loss heat to the PCB, which dissipates it.
When you are ready with this task, your board will look terrible with all that molten, burned and blackened flux residue! But don't despair: Place the power supply in such a position that any liquid on the solder side of the board can drip off, and now take a small paintbrush, a bottle of alcohol, and applying generous amounts of this magic liquid brush all of the ugly black rosin dirt away!
Check that there is no continuity between the AC input and ground, between the AC input and the DC output, or between the DC output and chassis ground. Connect a variable voltage supply (you need 12 to 15V for the tests) to the output leads, without plugging the switcher to the AC line. If this works, you will at least get a confidence boost! If you have a dual-channel oscilloscope, connect its two channels over the base-emitter junctions of the power transistors. If you want, you can preadjust VR2 by setting your lab power supply to 13.8V and then setting VR2 just to where the pulses disappear. Remove your lab supply, remove the oscilloscope leads, and connect the beast to the AC line in series with a 60 Watt light bulb.
At this load level, probably the bulb in the AC line will glow, while the voltage on the output may be 13.8V or somewhat below. It depends on the specific current level drawn by your test load. If so far everything is OK, the big moment comes: Remove the bulb from the AC circuit!



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