Introduction: Cheap Volts!
http://www.macaulayaudio.co.ukThereis nothing more frustrating than finding out that your power supply isn't up to powering your latest gizmo. Especially on a rainy Sunday afternoon when your chances of buying any new components are zero. Well hereis a solution ,a simple circuit that provides a variety of dc voltages from the raw ac input of a transformer secondary.
That's exactly what this circuit does. It combines the functions of a voltage doubler, tripler and quadrupler . Connect your transformer secondary to its input and youll get 2, 3 or 4 times the input ac voltage as dc, dependent on where you take your output.
I've used this circuit to provide dc voltages between 18-200V dc with transformer secondaries from 6VAC-40VAC.40VAC is a practical limit to this board because of the voltage rating of the caps. Nevertheless I've operated relays motors and the odd valve circuit with this device.
First the usual disclaimer. I accept no responsibility whatever for the way in which this unit is used and /or any injury or damage it might cause. Actually there's not a lot that can go wrong with it used in the way described here. To make life easier you can get a complete kit of parts for this project for £4.99 and yes we'll despatch it to anywhere in the world, airmail for £1, yes anywhere in the world. For more info visit my website. This is probably less than you would be able to make it for yourself considering minimum order prices and the cost of strip-board etc.
As you can see from the circuit diagram the device is a modified voltage quadrupler with multiple voltages taken from various points in the circuit.
The parts youll need are listed below:-
D1,2,3 and 4 = 1N4007
C1,2,3,4 = 100uF/100V
Strip-board panel 11 strips x 22holes
6W Terminal block
3mm Thick plastic panel 55mm x 83mm
3 M3 x 16mm screw, nuts
The circuit diagram is shown below. AC power from the transformer secondary is fed through the Capacitor Diode network to produce rectified multiples of the input voltage. In fact the circuit consists of several half wave rectifiers in series. The only disadvantage of the circuit is that the ripple voltage tends to be a bit high but this can be helped by connecting a further smoothing cap(s) in parallel with the output terminals. When driving relays motors and other such devices this is irrelevant.
So much for the theory, how about construction? To keep costs down Ive used a piece of 0.1 matrix copper clad strip-board measuring 11 strips by 22 holes across. Looking at the diagram this shows the layout. Note that 'X' indicates a break in the track and these should be made with a suitable cutter at the places indicated. This is the first task of construction. Next drill the hole in the panel at F13 to take a 3mm screw.
It's almost a must to mount the diodes first. Otherwise youll end up struggling trying to insert them between the caps.(take it from me! ) Also it makes life easier to temporarily hold components into position with a piece of masking tape to stop slippage when soldering. Note that the diodes are soldered the right way round. Polarity is indicated by the light band at one end of the component.
Next install the electrolytic capacitors C1-4. Again these are polarised as indicated both on the component body and layout diagram. At this stage the board is finished and can be put on one side while attention is turned to the plastic panel.
The panel performs two practical tasks. Firstly and obviously it holds the project together but it also insulates the circuit from the outside world and making it easy to fasten into a metal case by means of a couples of M3 screws.
The plastic panels are available in most model shops in A4 sheets for a couple of quid and are easy to cut into smaller panels by marking them out and cutting along the lines with a scalpel. A Mechanical drawing is shown for the panel below. Simply mark out your plastic panel and drill the M3 clearance holes and this task is completed.
Lastly final construction. Attach flying leads to the board at the points indicated leaving these about 6(150mm) long. Mount the board with an M3 screw and tighten it down to the plastic panel. Similarly mount the terminal block and connect the ends of the flying leads as shown in the layout diagram. The project is now ready to use.