short pulses for radiant circuits

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Short Pulses for Radiant Circuits

[Geben Sie den Untertitel des Dokuments ein]

28.04.2012

0.1 / Draft

Short Pulses for Radiant Circuits 28.04.2012

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Table of Contents

1 Overview .......................................................................................................................................... 2

1.1 Disclaimer: ............................................................................................................................... 2

1.2 Policies: .................................................................................................................................... 2

1.3 Abbreviations: ......................................................................................................................... 2

2 Recalling Basics ................................................................................................................................ 3

2.1 Inductances ............................................................................................................................. 3

2.2 Transformers – Common Operation ....................................................................................... 3

2.3 Lenz’s Law and Other Laws ..................................................................................................... 5

2.4 Transformers – Pulse Operation ............................................................................................. 6

2.5 Pulses for Radiant Circuits ....................................................................................................... 7

2.6 Effect of Pulse Width ............................................................................................................... 7

3 Pulse generation .............................................................................................................................. 9

3.1 Pulse transformer in current mode ......................................................................................... 9

3.2 Spark gaps – tesla mode ........................................................................................................ 10

3.3 Pulsing oscillating coils .......................................................................................................... 11

3.4 Pulsing Don Smith circuits ..................................................................................................... 11

3.5 Capacitor Discharge Ignition (CDI)......................................................................................... 11

3.6 Nanosecond Pulses ................................................................................................................ 13

Image Directory

Figure 1 - Flywheel .................................................................................................................................. 3

Figure 2 - Voltage and current (sine wave) ............................................................................................. 4

Figure 3 - Magnetic vortex ...................................................................................................................... 4

Figure 4 - Pulsed transformer .................................................................................................................. 6

Figure 5 - Fourier transformation ............................................................................................................ 7

Figure 6 - Automotive ignition system .................................................................................................... 9

Figure 7 - Tesla's pulse technology (example) ....................................................................................... 10

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1 Overview Many radiant circuits require short and high voltage pulses in order to trigger radiant events. While

radiant science is still off the trail of the publicly accepted science it cannot abandon dead normal

circuitry in line with normal science in order to succeed.

Many replications show lag of basic knowledge and therefore do not succeed despite extraordinary

enthusiasm.

This workout tries to bring these essential basics to the mind of mere mortals. Math was omitted

wherever possible. It is the expressed goal to support enthusiastic replicators and give them some

tools and thought food being necessary to build successful setups.

This text covers some basic notions regarding inductances and transformers. Transformers own some

properties being overseen by most replicators. Generating short pulses is not difficult but is quite

different from normal operation of ignition coils. Another part of the document covers hints for

adapted circuits and explanations of their function.

This document does not contain schematics ready for copy and paste. Please understand the content

as toolbox and tutorial related to pulse generation.

1.1 Disclaimer:

The content is intended for tutorial purpose only. The setups discussed produce lethal voltages and

you are not encouraged to build or operate them as long you are not an educated person with

knowledge regarding safe operation of lethal voltages.

The text covers notions of the author. Despite widely common request he will not enter any

discussion regarding scientific proof. Facts need to be evaluated and compared with other before.

The scientific proof is the last action only. Nobody is forced to follow these notions

1.2 Policies:

You are encouraged to copy and forward this document at will as long as the content is not modified.

Quotations are allowed unmodified only with added reference (title, version ).

1.3 Abbreviations:

HV = High Voltage

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2 Recalling Basics

2.1 Inductances

Inductances are well known to resist current changes vehemently.

Imagine a flywheel. The accelerating force conforms to the voltage and the rotation speed to the

current. Conform standard notion the energy is stored in the magnetic field. Apart that other notions

exist proposing that the magnetic field is one effect only while other procedures are involved as well.

Figure 1 - Flywheel

If we try to stop a flywheel we need to deplete the stored energy. Too sudden breaking will unleash

enormous forces because of the inertia of the mass. In electric terms the stop action conforms to

interrupting the current. – enormous voltage will occur because of the “inertia” of the magnetic field.

2.2 Transformers – Common Operation

The common notion is that transformers transform voltages from one level to another level and

along that they feed loads with the requested current. Unfortunately this is not the whole truth and

therefore transformers are widely misunderstood.

This chapter will not cover the whole transformer theory but some important highlights only.

In fact there is no case known where a transformer (ignition coils included) transformed voltages. I

admit that the effects are measurable but these are effects only and not the intrinsic function of a

transformer. Apart that the transforming of voltages measured conforming n1:n2 (winding ratio) is

true for one single case out of thousands. It is the sine wave voltage being replicated at the output

winding. For other cases see next chapter.

As a transformer is an inductance it will behave like an inductance if we apply voltage at its primary

winding. Contrary to the common notion the secondary voltage is not dependent to the primary

voltage directly but to the changing current through the primary winding. This corresponds to the

magnetic flux generated. This is a very essential difference – it will be recalled below.

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Figure 2 - Voltage and current (sine wave)

Imagine the red line above to be the shape of the input voltage. The blue line corresponds to the

current in the primary winding.

The voltage shows a positive crest at 1/2PI and a negative crest at 3/2PI. The crest area is a point

where the voltage does not change for a short time. In fact there a positive slope converts to a

negative slope and vice versa. In-between the crests there is a point (PI and 2PI) where the change

rate of the voltage is maximum (negative slope at PI and at 2PI positive slope).

The current will show its greatest change at the maximum voltage (1/2PI) or minimum voltage

(7/4PI) respectively. In-between (PI or 2PI) the current shows its crest because from now on the

voltage will drive it in the opposite direction. The notion is that the current shows a sine shape as

well but ½ wave lengths delayed.

The output voltage is a representation of the current change rate. That is: the current change

controls the voltage generated in the output windings.

• The input voltage drives the current changes

• The current drives the magnetic flux but the flux resists like a flywheel (inertia)

• Due to the “inertia” of magnetic fields there is a delay of ¼ wave length.

• The change of flux generates the voltage at the output winding

Imagine the output wave form being a display of the change rate of the input wave form in every

minute slice of time.

The notions above cover the forward transfer of energy. Unfortunately trasformers suffer an a

reverse action as well.

Note: Apart the standard notion of a linear flow of magnetic flux there is evidence that magnetic

fields propagate in vortex shape. So please understand that the standard science presents a

simplified thinking model only.

Figure 3 - Magnetic vortex

Please read the very interesting booklet “The secret world of Magnets” by Howard Johnson

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2.3 Lenz’s Law and Other Laws

If at a transformer the load draws current on the secondary winding it intervenes with the flux as

well and reduces the inductance at the primary winding. Thus current changes happen faster at the

primary side and the current increases as well. This behavior is called Lenz’s law and corresponds

very well to the thermodynamic laws employed by standard science (conservation of energy).

Unfortunately the thermodynamic laws are based on the notion that we have closed systems. These

were invented in the 19th

century in the times of Mr. Carnot. He was the first who measured the heat

energy of input (coal) and compared it to the heat loss and the usable energy on the shaft of the

flywheel. He proved that the input energy corresponds very well with the sum of the output.

Fortunately nature does not know closed systems at all and does not care for scientific notions. In

fact the idea of a closed system is a simplification in order to grasps some details – but SOME details

only.

For understanding open and closed systems imagine the following story:

You are a modern scientist and you decided to travel by ship. Everybody knows that a ship is a closed

system and you need oil in order to drive its hull through the water. You know that the energy

entered in the engine corresponds to the sum of thermal losses (exhaust, engine cooling) and the

shaft energy being used to move the ship. In the end ALL your energy will be transformed into heat.

This is called entropy and it is a low of nature. No doubt left! Other disturbances are of negligible

magnitude.

But there are incurable guys who ignore all your knowledge and do very silly things. They build so

called sail boats. They dare to account for negligible side effects barely measurable at a motor ship.

Of course they invest energy for setting the sails – poor guys! Look how they sweat working by their

own hands! Unfortunately - shortly after - these mad brains pass your motor ship with ease.

They obviously use an open system provided by creation but being neglected by science. They make

use of an energy system being outside of Carnot’s enclosed steam engine. These outside energies will

interfere in minute extend with the closed systems but perform extremely well if we open the stuffy

chamber of Carnot’s chamber.

Similar to Carnot Lenz’s law is one pane only of the real crystal. This pane focusses on a closed

system only. Utkin, Zilano and others show additional panes (i.e. cw/ccw secondary, one short

circuited).

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2.4 Transformers – Pulse Operation

I we talk of short pulses it is self-evident that we have no sine shape but something like a square

wave. For initial consideration a square wave of 50% duty cycle will suffice in order to study the basic

behavior.

Figure 4 - Pulsed transformer

We recall:

• The voltage jumps between high and low voltage (dotted line = 0V) [a)]

• We expect the current to increase and decrease on a regular basis. Within the operation area

of the core the current change will be linear (see green graph below).[b)]

• The current slope will generate a low voltage at output winding (increasing slope = positive

voltage / decreasing slope negative voltage).[c)]

• When the voltage changes the polarity there is a sudden change in current change as well

and the output voltage will show a very short peak direction. (d)

Recall the notion above: “Imagine the output wave form being a display of the change rate of the

input wave form in every minute slice of time.” It is a kind of “accelerometer” showing the speed

of change of the voltage.

It is important to note that the voltage of the short peak is of course dependent on the turn ration

n1:n2 but is dependent on the current change as well. Sudden changes in current change determine

the output voltage considerably.

We see that sine wave mode is a very special case for a transformer. We need to overcome this

simplification in order to understand the behavior of other wave forms. Exactly this fact shown above

gives several degrees of freedom in order to create very different circuits for pulse generation.

a)

b)

c)

d) b)

c)

d)

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2.5 Pulses for Radiant Circuits

Conforming Tesla’s notion pulses initiate radiant activities beginning with 20 kHz and above. If we

want to follow tesla we should generate such pulses and not try any short cut. Short cuts often force

us to return later thereto and go the predefined way.

The frequency of 20 kHz corresponds to a frequency period of 50 µs. The pulse time corresponds to

the half period time = 25µs!! This seems not to be true at brute force sparks with fantastic light

effects. These sparks can’t be silent because of intermittent release of enormous shocks to the air.

Tesla mentioned again and again that the spark gaps need to be “thoroughly adjusted”. Depending

on the specific circuit the sparks will be conforming the requirement above (<25µs). Tesla used

quenched spark gaps in order to get pulses short enough and in precise sequence.

The pulsed operation mode above shall not be confused to another operation mode where

the sparks follow the oscillations of the tank circuit. In the latter case they might be AC as

direct image of the tank frequency. But we will focus here to the short DC pulses.

2.6 Effect of Pulse Width

Conforming the standard theory every regular shape of wave form can be synthesized by proper

mixing of sine waves of different frequency and amplitude. Conversely a given pulse shape can be

examined for content of sine frequencies. These intrinsic frequencies are real because tank circuits of

adapted resonant frequency can be excited.

The facts mentioned above can be derived in a highly mathematical manor (invented by Mr. Fourier)

but it can be explained by a simple graph as well.

Please note that the graph below is an example only. It is not a true representation of

different wave forms discussed in chapters below.

Modern scopes often can do the Fourier math for a waveform recorded in order to display

such a graph directly along with measurement functions.

Figure 5 - Fourier transformation

This representation above shows the frequencies found in a specific wave form. Every vertical blue

line represents a certain frequency, amplitude and amount of energy contained in the specific signal.

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The most left blue bar represents the basic frequency of the pulse – being a sine wave as basic

component. More frequencies are found – all sine waves which add to the basic frequency in order

to form the specific wave form of the pulse.

Now imagine the red vertical line to represent a frequency of 20 kHz (pulse 25ns). Tesla states that

our pulse should comply. All components at right hand side from the red line will comply and all at

left hand side will not comply.

Conclusion: The five frequencies at left hand side waste a considerable amount of our pulse energy

not being part of the radiant party.

In order to overcome this loss of energy the input signal needs to be increased considerably. The

smart way would be to generate pulses short enough.

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3 Pulse generation With the notions above in mind we can proceed to specific methods of HV pulse generation including

an evaluation of their performance. All setups below make use of a pulsed HV transformer and the

focus is on the method to kick it in the right way.

3.1 Pulse transformer in current mode

This is the standard ignition technology in automotive systems. Let’s have a look to the electronic

controlled variant directly. The usual winding ratio of an ignition coil is 1:100.

Figure 6 - Automotive ignition system

Recall “Figure 4 - Pulsed transformer” above -> first pulse.

• The transistor switches the ignition coils primary to ground and enables the current to flow.

• The current will increases in a linear manor up to 5 or 8 A. Along the current increase the

magnetic flus increases (Imagine an accelerating flywheel).

• Along the current increase the output coil will generate a moderate negative voltage being of

no practical use or disadvantage.

• In the very moment when the ignition spark is requested the transistor will open the current

path. The current is violently forced to stop flowing.

• The energy stored discharges via the spark plug.

The output voltage is dependent on the winding ration, the transistor switch time and the last value

of current flowing.

Unfortunately it is not easy to switch a transistor off because of some tradeoffs being connected with

the transistor itself.

• The BE junction contains a small capacitor and switching the base to ground is no fast

switching.

• Additionally there is a CB capacitance contained as well. Steep increase of collector voltage

(intended at ignition coils) adds some current to the base putting an extra demand on the

base driver.

• Transistors get lazy if they much collector current and much lazier if they get too much base

current. The tuning of transistor is not trivial. Their operation needs to be done conforming

their specification. It is easy to get a transistor vibrate somehow. But if we intend to get it

cool and fast, the facts mentioned above needs to be considerate. Let’s assume that our

transistor needs about 5µs in order to shut down 5 amps (corresponds to a slope of 1

amp/µs)

High Voltage

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Unfortunately it is worse:

The automotive ignition was invented by Tesla as well and he definitely knew what he did. The

automotive ignition system is a current employing system optimized for energy transfer. A gas

mixture needs a certain amount of spark energy in order to start a reliable combustion and it needs it

for a relatively long amount of time. The high voltage is necessary for first spark ignition only

followed by a plasma arc burning at about 600V. The sparking time is about 500µs up to 1ms.

These advantages for a gas combustion convert to disadvantages if employed for short radiant

pulses. The main disadvantage is that the ignition coil needs a certain amount of primary current in

order to produce high enough voltage if the current is interrupted. The stored energy at this time of

interruption is high enough in order to feed a long burning time of the plasma. Apart that there is a

vast amount of energy left if the spark interrupts so final oscillations will occur. Sometimes a second

reverse spark will occur. Additionally the long spark time is far away from 25 µs.

3.2 Spark gaps – tesla mode

Tesla in his time had no semiconductors available and vacuum valves arose in the 19th century long

after his groundbreaking discoveries. It is interesting to note that Tesla never used the automotive

ignition scheme at his radiant circuits.

Figure 7 - Tesla's pulse technology (example)

He kicked the primary coils with short HV voltage pulses. This technology is not an amperage

technology like automotive ignition systems but a high voltage technology. Nevertheless he made

use of the method of current change - BUT BEFORE high currents build up. The focus here is high

voltage / short pulse and NOT high energy and long burning time.

If we recall “Figure 4 - Pulsed transformer” it is not essential if we get the current increased suddenly

or stopped. Tesla shoots a small charge out of the primary capacitor to the coil. Because of high

voltage he initiates a very steep current slope. He does not need much current but just the current

slope for short time. There spark stops earlier and the rest energy in the coil is much less compared

to the automotive ignition system.

The notions above apply to parallel or serial spark gaps. The final effect is the same. In fact it is quite

easy to get pulses below 100µs. Tuning is quite easy: capacitance and voltage.

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3.3 Pulsing oscillating coils

Especially at this circuit above, repetitive sparking should enhance the oscillation of the coil and NOT

decrease oscillations. If we pulse brute force at any deliberate time asynchronously we may hit the

coil in a moment where we cancel the oscillating energy within the coil. Sudden stop of oscillation

will occur and restart at the next spark. At extreme brute force any state of the resonant coil will be

overridden and reset to a new oscillating sequence.

This document will not cover more details regarding synchronous sparking or multi sparking. It is felt

to be important mentioning this detail along Tesla’s circuits. For more details see i.e. the animation

here.

3.4 Pulsing Don Smith circuits

Don Smith rearranged Tesla’s technology because he had available modern electronic components.

So the primary pulsing brings no additional notions.

Excursus:

But Don used another pulse system not being obvious. It is corroborated that Don - at end of

his life - admitted that his technology may function without resonant coils. If that is true then

the magic happens in the capacitors being pulsed severely. Once again we need pulses as

short and high as possible.

His resonant coil performed exactly that: Pulses of 0.5µs (corresponds to 1 MHz -< pos. and

neg. cycle rectified) or less through the diodes and high voltage onto capacitors. It works with

or without cw/ccw coils! But it is essential to have fast switching diodes – 10% of pulse time

recommended. And of course we need capacitors being able to admit such pulses without

being a low pass filter for mains frequency only.

3.5 Capacitor Discharge Ignition (CDI)

After discussing different systems for pulse generation there is one left and surprisingly – it is

currently used for automotive racing applications and motorcycles as well. It is a modern replication

of Tesla’s technology. The circuits are simple and understandable easily – much more if someone

dealt with Tesla’s circuits before.

For automotive applications a short spark is a severe drawback. They overcome this disadvantage by

firing multiple sparks being short and of very high energy. (up to five). If we omit the multiple sparks

the CDI circuit gets more easily and will perfectly fit to radiant circuits.

Let’s take the standard circuit from Figure 6 and replace the 12 V battery voltage by a capacitor

precharged to 300V DC. (The transistor should be a high voltage type).

High Voltage

300V

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If we switch the transistor on the capacitor will discharge within a short time through the primary

winding.

The conditions changed considerably compared to the standard ignition circuit:

• The basic circuit corresponds to Teslas’s basic circuit except the switch element is now

related to ground. Pluralities of other configurations are possible but this is best for

explanation.

• We get the spark just short after the trigger signal and we deed not precharge the coil

before.

• Because of the high input voltage the current rise is very steep and exactly this converts in

the end in a very high voltage at the output. Please note: We don’t need high current in the

primary winding but high current increase. At the end of the HV pulse at output we have

much less energy stored in the magnetic field.

• The transistor is not loaded with so much current like before in the standard ignition circuit.

• The capacitor charge and voltage determines the pulse time for a given inductance.

• The switch off speed is irrelevant because the charge of the capacitor will be exhausted

before we shut the current path.

• A too high base current speeds the switch on time up, while slowing down the switch off

time - but the latter is irrelevant (see above)

• The transistor will switch very fast ON because it will deal with a minute current at this time

– the coil prevents instant high current.

• The best news is: the pulse time being at output being less than 80 µs at automotive CDI

ignition systems and this value can be drilled down by proper tuning.

• Standard ignition coils can be used as long the output voltage is not driven higher than max.

ratings.

Please understand that this example explains the basic principle only and is not a

thorough suggestion for easy copy and paste. You are requested to understand the

matter and develop own circuits for your special application.

In Summary: A CDI circuit is a simple circuit producing short high voltage pulses with fewer

implications compared to a standard ignition circuit being based mainly on current flow.

And please note that CDI circuits follow Tesla’s circuits.

The question is left: How to recharge the capacitor above?

(Schematic generated with KiCad)

Here is one of a plurality of different possibilities.

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The recharge is performed by L1 / D1. If the transistor is in standby state the capacitor C2 will be fully

charged. In the moment of discharging C2 through TR1 the coli L1 will block a sudden recharge. This

is essential in order to not recharge C2 too early. (Else we get a standard automotive circuit and

destructive long pulses.). After spark event and the transistor being inactive the coil L1 gets active,

the current flows to C2 up to full charge (HV input voltage).

The good news is that an inductance behaves similar to a flywheel. The current will not stop if C2 is

fully charged to the voltage of C1 but will be charged about twice the HV DC voltage at input. D1

blocks the current from flowing back to C1. Only the very first HV pulse at output will show less HV

and will be shorter.

Properly tuned this circuit will recharge C2 at a big range of frequencies to a very constant voltage at

C2.

The HV generation (300V) is not discussed here. Some suggestions can be found in the linked

schematics below or at good sites from Tesla coilers.

The following links show some schematics for CDI circuits. Study them and find your

genuine application.

An example for a CDI circuit:

another

another

another

another

simplest circuit scroll down

Application note from STM

another

BTW: see the pic there. Left normal spark and right hand spark with prallel

cap. There we see what Tesla stated regarding the cap before spark gap..

3.6 Nanosecond Pulses

The text above focusses on simple pulse generation not shorter than some µs. Research and laser

applications require pulses far shorter in the range of nanoseconds or picoseconds. It is important to

know that electronic parts can do it but this is no standard technology. They use step recovery

diodes, nonlinear transmission lines or cascode connection technology. Her an example: A 500V

nanosecond pulse generator using cascode-connected power MOSFETS.

~o0o~