One component which has been shown but not described is the diode or ‘rectifier’

The Diode
One component which has been shown but not described is the diode or ‘rectifier’.   This is a device which has a very high resistance to current flowing in one direction and a very low resistance to current flowing in the opposite direction.   The base/emitter junction of a transistor is effectively a diode and, at a push, can be used as such.   A proper diode is cheap to buy and has far greater voltage and current handling capacities than the base/emitter junction of a transistor.

Diodes are mainly made from one of two materials: germanium and silicon.   Germanium diodes are used with very small alternating currents such as radio signals coming from an aerial.   This is because a germanium diode needs only 0.2 Volts or so to carry a current while silicon needs 0.6 to 0.7 Volts (same as a silicon transistor base/emitter junction).   Germanium diodes (and transistors) are very sensitive to temperature change and so are normally restricted to low power circuits.   One very neat application for a silicon diode is as an ‘un-interruptible power supply’ where mains failure is caught instantly:

In this circuit, the mains voltage drives the Power Supply Unit which generates 12 Volts at point ‘A’.   This provides current to the Load.   The diode has +12 Volts at ‘A’ and +12 Volts at point ‘B’ so there is no voltage drop across it and it will not carry current in either direction.   This means that the battery is effectively isolated when the mains is functioning.   If the Power Supply Unit output were to rise above its design level of +12 Volts, then the diode would block it from feeding current into the battery.

If the mains fails, the Power Supply Unit (‘PSU’) output will fall to zero.   If the battery and diode were not there, the voltage at point ‘A’ would fall to zero, which would power-down the Load and possibly cause serious problems.  For example, if the load were your computer, a mains failure could cause you to lose important data. With a battery back-up of this type, you would have time to save your data and shut your computer down before the battery ran out.

The circuit operates in a very simple fashion.   As soon as the voltage at point ‘A’ drops to 0.7 Volts below the +12 Volts at point ‘B”, the diode starts feeding current from the battery to the Load.   This happens in less than a millionth of a second, so the Load does not lose current.   It would be worth adding a warning light and/or a buzzer to show that the mains has failed.

Diodes are also supplied packaged as a diode bridge, with four diodes enclosed inside. Usually intended for power supply rectification, they are not particularly fast-acting diodes, but are cheap and can carry a good deal of current. A common size is with the diodes rated at 1000 volts and able to carry 35 amps. Although there are many package types, a very common package looks like this:

The alternating signal is connected between two opposite corners and the pulsating DC is taken off from the other two terminals. The symbols shown above are normally marked on the flat face which is not seen in this picture. The package has a hole in the centre so that the metal case can be bolted to a heat-sink in order to keep the device reasonably cool when carrying large currents. The connections inside the package are like this:

It is possible to connect the bridge in a different way and use it as a higher voltage double diode arrangement as shown here:

By skipping the alternating current ability and connecting to just the Plus and the Minus terminals, the package provides two pairs if diodes in connected in series. This gives twice the voltage handling in both current paths and the rated current handling capacity in both of those two paths which are now connected across each other, which doubles the current handling capacity. The diagram shows how three ordinary, cheap 1000V 35 amp bridges can be connected to give one 70 amp 6000V composite diode. You could, if you wish, raise the specification of a 1000V 35A diode bridge to 2000V 70A by using four of them like this:

Diodes are specified by their voltage handling capacity and their current-carrying capacity and the speed at which they can switch on and off. For power supplies where the frequency is very low, any diode will do, but there are circuits where the switching is needed hundreds of thousand times per second and so the diode specification sheets need to be checked to see what frequency can be handled by any particular diode. Those data sheets can be downloaded free from

One other thing which needs to be checked for some circuits is the voltage needed to get the diode to switch on. Two common materials used when making diodes are silicon and germanium. Germanium types have a low forward voltage of around 0.2 volts typically which silicon has about a 0.6 volt threshold generally. These voltage figures vary enormously as the current through the diode increases. Circuits which use very low voltages need germanium diodes such as the 1N34

There is a widely used variation of the diode which is extremely useful, and that is the Light Emitting Diode or ‘LED’.   This is a diode which emits light when carrying current.   They are available in red, green, blue, yellow or white light versions.   Some versions can display more than one colour of light if current is fed through their different electrical connections.

LEDs give a low light level at a current of about 8 or 10 mA and a bright light for currents of 20 to 30 mA. If they are being used with a 12 Volt system, then a series resistor of 1K to 330 ohms is necessary.   LEDs are robust devices, immune to shock and vibration.   They come in various diameters and the larger sizes are very much more visible than the tiny ones.

SCRs and Triacs:
Another version of the diode is the Silicon Controlled Rectifier or ‘Thyristor’.   This device carries no current until its gate receives an input current.   This is just like the operation of a transistor but the SCR once switched on, stays on even though the gate signal is removed.   It stays on until the current through the SCR is forced to zero, usually by the voltage across it being removed.   SCRs are often used with alternating voltages (described below) and this causes the SCR to switch off if the gate input is removed.   SCRs only operate on positive voltages so they miss half of the power available from alternating power supplies.   A more advanced version of the SCR is the ‘Triac’ which operates in the same way as an SCR but handles both positive and negative voltages.

Another very useful variation on the LED is the Opto-Isolator.   This device is a fully enclosed LED and light-sensitive transistor.   When the LED is powered up, it switches the transistor on.   The big advantage of this device is that the LED can be in a low voltage, low power sensing circuit, while the transistor can be in a completely separate, high voltage, high power circuit.   The opto-isolator isolates the two circuits completely from each other.   It is a very useful, and very popular, low-cost device.

Alternating Current:
A battery provides a constant voltage.   This is called a Direct Current or ‘DC’ source of power.   When a circuit is connected to a battery, the positive rail is always positive and the negative rail is always negative.

If you connect a battery to a circuit through a double-pole changeover switch as shown here:

When the changeover switch is operated, the battery is effectively turned over or inverted.   This circuit is called an ‘inverter’ because it repeatedly inverts the supply voltage.   If the switch is operated on a regular, rapid basis, the graph of the output voltage is as shown on the right.   This is a ‘square wave’ voltage and is used extensively in electronic equipment.   It is called alternating current or ‘AC’ for short.   SCRs and Triacs can be used conveniently with supply voltages of this type.   Mains voltage is also AC but is rather different:

Mains voltage varies continuously in the form of a sine wave.   In Britain, the mains voltage is described as ‘240 Volts AC’ and it cycles up and down 50 times per second, i.e. 50 positive peaks and 50 negative peaks in one second.   It would be reasonable to assume that each voltage peak would be 240 Volts but this is not the case.   Even though the supply is described as 240 Volts, it peaks at the square root of 2 times greater than that, i.e. 339.4 Volts.   The actual supply voltage is not particularly accurate, so any device intended for mains use should be rated to 360 Volts.   In America, the supply voltage is 110 Volts AC and it cycles 60 times per second, peaking at plus and minus 155 Volts.   Later on, you will see how one or more diodes can be used to convert AC to DC in a unit which is sold as a ‘mains adapter’ intended to allow battery operated equipment be operated from the local mains supply.

If you take a cardboard tube, any size, any length, and wind a length of wire around it, you create a very interesting device.   It goes by the name of a ‘coil’ or an ‘inductor’ or a ‘solenoid’.

This is a very interesting device with many uses.   It forms the heart of a radio receiver, it used to be the main component of telephone exchanges, and most electric motors use several of them. The reason for this is if a current is passed through the wire, the coil acts in exactly the same way as a bar magnet:

The main difference being that when the current is interrupted, the coil stops acting like a magnet, and that can be very useful indeed.   If an iron rod is placed inside the coil and the current switched on, the rod gets pushed to one side.   Many doorbells use this mechanism to produce a two-note chime.   A ‘relay’ uses this method to close an electrical switch and many circuits use this to switch heavy loads (a thyristor can also be used for this and it has no moving parts).

A coil of wire has one of the most peculiar features of almost any electronic component.   When the current through it is altered in any way, the coil opposes the change.   Remember the circuit for a light-operated switch using a relay?: 

You will notice that the relay (which is mainly a coil of wire), has a diode across it.   Neither the relay nor the diode were mentioned in any great detail at that time as they were not that relevant to the circuit being described.   The diode is connected so that no current flows through it from the battery positive to the ‘ground’ line (the battery negative).   On the surface, it looks as if it has no use in this circuit.   In fact, it is a very important component which protects transistor TR3 from damage.

The relay coil carries current when transistor TR3 is on.   The emitter of transistor TR3 is up at about +10 Volts.   When TR3 switches off, it does so rapidly, pushing the relay connection from +10 Volts to 0 Volts.   The relay coil reacts in a most peculiar way when this happens, and instead of the current through the relay coil just stopping, the voltage on the end of the coil connected to the emitter of TR3 keeps moving downwards.   If there is no diode across the relay, the emitter voltage is forced to briefly overshoot the negative line of the circuit and gets dragged down many volts below the battery negative line.   The collector of TR3 is wired to +12 Volts, so if the emitter gets dragged down to, say, -30 Volts, TR3 gets 42 Volts placed across it.   If the transistor can only handle, say, 30 Volts, then it will be damaged by the 42 Volt peak.

The way in which coils operate seems weird.   But, knowing what is going to happen at the moment of switch-off, we deal with it by putting a diode across the coil of the relay.   At switch-on, and when the relay is powered, the diode has no effect, displaying a very high resistance to current flow.   At switch-off, when the relay voltage starts to plummet below the battery line, the diode effectively gets turned over into its conducting mode.   When the voltage reaches 0.7 Volts below the battery negative line, the diode starts conducting and pins the voltage to that level until the voltage spike generated by the relay coil has dissipated.   The more the coil tries to drag the voltage down, the harder the diode conducts, stifling the downward plunge.   This restricts the voltage across transistor TR3 to 0.7 Volts more than the battery voltage and so protects it.

Solenoid coils can be very useful.   Here is a design for a powerful electric motor patented by the American, Ben Teal, in June 1978 (US patent number 4,093,880).   This is a very simple design which you can build for yourself if you want.   Ben’s original motor was built from wood and almost any convenient material can be used.   This is the top view:

And this is the side view:

Ben has used eight solenoids to imitate the way that a car engine works.   There is a crankshaft and connecting rods, as in any car engine.   The connecting rods are connected to a slip-ring on the crankshaft and the solenoids are given a pulse of current at the appropriate moment to pull the crankshaft round.   The crankshaft receives four pulls on every revolution.   In the arrangement shown here, two solenoids pull at the same moment.

In the side view above, each layer has four solenoids and you can extend the crankshaft to have as many layers of four solenoids as you wish.   The engine power increases with every layer added.   Two layers should be quite adequate as it is a powerful motor with just two layers.

An interesting point is that as a solenoid pulse is terminated, its pull is briefly changed to a push due to the weird nature of coils.   If the timing of the pulses is just right on this motor, that brief push can be used to increase the power of the motor instead of opposing the motor rotation.   This feature is also used in the Adams motor described in the ‘Free-Energy’ section of this document.

The strength of the magnetic field produced by the solenoid is affected by the number of turns in the coil, the current flowing through the coil and the nature of what is inside the coil ‘former’ (the tube on which the coil is wound).   In passing, there are several fancy ways of winding coils which can also have an effect, but here we will only talk about coils where the turns are wound side by side at right angles to the former.

  1. Every turn wound on the coil, increases the magnetic field.   The thicker the wire used, the greater the current which will flow in the coil for any voltage placed across the coil.   Unfortunately, the thicker the wire, the more space each turn takes up, so the choice of wire is somewhat of a compromise.

  2. The power supplied to the coil depends on the voltage placed across it.   Watts = Volts x Amps so the greater the Volts, the greater the power supplied.   But we also know from Ohm’s Law that Ohms = Volts / Amps which can also be written as Ohms x Amps = Volts.   The Ohms in this instance is fixed by the wire chosen and the number of turns, so if we double the Voltage then we double the current.

    For example: Suppose the coil resistance is 1 ohm, the Voltage 1 Volt and the Current 1 Amp.   Then the power in Watts is Volts x Amps or 1 x 1 which is 1 Watt.

    Now, double the voltage to 2 Volts.   The coil resistance is still 1 ohm so the Current is now 2 Amps.   The power in Watts is Volts x Amps or 2 x 2 which is 4 Watts.   Doubling the voltage has quadrupled the power.

    If the voltage is increased to 3 Volts.   The coil resistance is still 1 ohm so the Current is now 3 Amps.   The power in Watts is Volts x Amps or 3 x 3 which is 9 Watts.   The power is Ohms x Amps squared, or Watts = Ohms x Amps x Amps.   From this we see that the voltage applied to any coil or solenoid is critical to the power developed by the coil.

  3. What the coil is wound on is also of considerable importance.   If the coil is wound on a rod of soft iron covered with a layer of paper, then the magnetic effect is increased dramatically.   If the rod ends are tapered like a flat screwdriver or filed down to a sharp point, then the magnetic lines of force cluster together when they leave the iron and the magnetic effect is increased further.
If the soft iron core is solid, some energy is lost by currents flowing round in the iron.   These currents can be minimised by using thin slivers of metal (called ‘laminations’) which are insulated from each other.   You see this most often in the construction of transformers, where you have two coils wound on a single core.   As it is convenient for mass production, transformers are usually wound as two separate coils which are then placed on a figure-of-eight laminated core.

However, while all that information is a useful, gentle introduction to what an inductor is, it does not convey the most important feature of a coil, which is that every coil stores energy when it is connected to a power source and it returns almost all of that energy when disconnected from the power source. The return of the stored energy happens in a very short period of time and that feature can produce powerful systems if you have the expertise to capture and use that power. 


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