Xenon Strobe Light Control Circuit

The circuits presented in the following article could be used for generating strobed lighting effect over 4 Xenon tubes in a sequential manner.

The proposed sequential xenon lighting effect could be applied in discotheques, in DJ parties, in cars or vehicles, as warning indicators, or as decorating ornamental lights during festivals.

A wide range of xenon tubes are available in the market with a matching ignition transformer set (that we are going to talk about afterwards). In theory, just about any xenon tube works extremely well in the strobe control circuit presented in figure below.

How Xenon Tube Rating is Calculated

The circuit is designed for a '60 Watts per second' xenon tube and this is all it is going to accommodate. Sadly, the power ratings of xenon tubes are typically mentioned as "x" watts per second, which often signifies an issue!

The reason behind the particular capacitor values in the diagram and DC voltage level may be comprehended through the following simple equation:

E = 1/2 C.U² 

The quantity of electrical power utilized by the xenon tube may be determined simply by multiplying energy and the xenon repetition pulse frequency.

With a frequency of 20 Hz and a power of 60 Ws, the tube might 'consume' around 1.2 kW! But that looks huge, and can't be justified. Actually, the mathematics in the above is using an incorrect formula.

As an alternative, this should be depending on the optimum acceptable tube dissipation and the resulting energy with respect to the frequency.

Considering that the xenon tube specifications which we are enthusiastic about should be capable of handling a highest possible dissipation up to 10 W, or an optimum level of 0.5 Ws energy should be discharged at 20 Hz.

Calculating the Discharge Capacitors

The above explained criteria calls for a discharge capacitance with a value 11uF and having an anode voltage of 300 V. As could be witnessed, this value matches relatively well with the values of C1 and C2 as indicated in the diagram.

Now the question is, just how do we select the correct capacitor values, in a situation where we have no rating printed on the xenon tube? Currently since we have with us the relationship between 'Ws' and W', the below shown rule-of -thumb equation could be tested out:

C1 = C2 = X . Ws / 6 [uF]

This is actually just a relevant clue. In case the xenon tube is specified with an optimal working range of under 250 continuous hours, it is best to apply the equation over a reduced allowable dissipation. A useful recommendation you may want to follow with regards to all types of xenon tubes.

Ensure that their connection polarity is proper, this means that, attach the cathodes to ground. In many instances, the anode is marked with a red-colored spot. The grid network is either available as like a wire at the cathode terminal side or simply as a third 'lead' between the anode and the cathode.

How Xenon Tube is Ignited

Alright, so inert gases have the ability to generate illumination when electrified. But this fails to clarify just how the xenon tube is actually ignited. The electrical power storage capacitor described previously is indicated in figure 1 above, through a couple of capacitors C1 and C2.

Given that the xenon tube needs a voltage of 600 V across the anode and the cathode, diodes D1 and D2 constitute a voltage doubler network in conjunction with the electrolytic capacitors C1 and C2.

How the Circuit Works

The a pair of capacitors are consistently charged to the maximum AC voltage value and as a result R1 and R2 are incorporated to restrict the current during the xenon tube's ignition period. If R1, R2 were not included the xenon tube would at some point degrade and stop working.

The resistor R1 and R2 values are selected to ensure C1 and C2 are charged up to the peak voltage level (2 x 220 V RMS) with the maximum xenon repetition frequency.

The elements R5, Th1 , C3 and Tr represent the ignition circuit for the xenon tube. Capacitor C3 discharges through the ignition coil's primary winding which generates a grid voltage of many kilovolts across the secondary winding, for igniting the xenon tube.

This is how the xenon tube fires and illuminates brightly, which also implies that now it instantly draws the entire electrical power held inside C1 and C2, and dissipates the same by means of a dazzling flash of light.

Capacitors C1, C2 and C3 subsequently recharges so that the charge allows the tube to go for a new pulse of flash.

The ignition circuit obtains the switching signal through an opto-coupler, an built-in LED and a photo transistor enclosed collectively inside a single plastic DIL package.

This guarantees excellent electrical isolation across the strobe lights and the electronic control circuit. As soon as the photo transistor is lit up by the LED, it becomes conductive and actuates the SCR.

The input supply for the opto-coupler is taken from the 300V ignition voltage from across C2. It is nonetheless lowered to 15V by diode R3 and D3 for apparent factors.

Control Circuit

Since the working theory of the driver circuit is understood, we can now learn how the xenon tube could be designed to produce a sequential strobing effect.

A control circuit for producing this effect is demonstrated in figure 2 below.

The highest repeat strobe rate is limited to 20 Hz. The circuit has the capacity to handle 4 strobe devices at the same time and essentially is made up of range of switching devices and a clock generator.

The 2N2646 unijunction transistor UJT works like a pulse generator. The network associated with this is intended to enable the frequency of the output signal to be tweaked around the 8 … 180 Hz rate using P1. The oscillator signal is fed to the clock signal input of the decimal counter IC1.

Figure 3 below shows a picture of the signal waveforms at the IC1 output with regards to the clock signal.

The signals coming from the IC 4017 switch at a frequency of 1 … 20 Hz are applied to the switches S1 … S4. The positioning of the switches decides the sequential pattern of the strobe. It allows the lighting sequence to be adjusted from right to left, or the opposite, etc.

When S1 to S4 are set at totally clockwise, the push-buttons become in the operational mode, enabling one of the 4 xenon tubes to be activated manually.

The control signals activate the LED driver stages through transistors T2 . . . T5. The LEDs D1 … D4 work like functional indicators for the strobe lights. The control circuit could be tested by just grounding the cathodes of D1 … D4. These will show immediately whether or not the circuit is working correctly.

A Simple Stroboscope using IC 555

In this simple stroboscope circuit the IC 555 works like an astable oscillator driving a transistor and an attached transformer.

The transformer converts 6V DC into 220 V low current AC for the stroboscope stage.

The 220 V is further converted to a high voltage peak 300 V with the help of the diode capacitor rectifier.

When the capacitor C4 charges up to the triggering threshold of the SCR gate neon bulb, through the resistive network, the SCR fires and triggers the driver grid coil of the stroboscope lamp.

This action dumps the entire 300 V into the stroboscope bulb illuminating it brightly, until the C4 is fully discharged for the next cycle to repeat.