Strobelight circuit operation

[Ali Sajjad]

I have an strobe light which flashes the xenon lamp at adjustable frequency. Triggering of the xenon lamp is done by applying a high voltage pulse at the trigger terminal of the lamp.I have seen strobe circuits using SCRs, but when i traced this circuit from my strobe light, i found that it is quite different from others. Can any one help me to understand how the circuit functions.

Regards
- Ali Sajjad

 

[ljcox]

I can't work out how it works. Are you sure the circuit is correct?

 

[McGuinn]

Is the transistor working like an AND gate, looking for both the 300VAC to be available and the pulse? It then passes a pulse to the step-up transformer which generates the HT pulse?

 

[Ali Sajjad]

yes the circuit is 100% correct. The stobe light is a commercial unit. I have also simulated the circuit in Circuitmaker version 5, and it gives the high voltage pulses at the trigger transformer output.
Well it does not work like an AND gate, as the 300 V power is DC not AC, and is always available.

 

[Styx]

yes the circuit is 100% correct. The stobe light is a commercial unit. I have also simulated the circuit in Circuitmaker version 5, and it gives the high voltage pulses at the trigger transformer output.
Well it does not work like an AND gate, as the 300 V power is DC not AC, and is always available.

mmm this is bugging me?

All I can see is that 100Ohm resistor is gonna be a power resistor.
It will draw 3A while the 1u charges up at power on. After that the RMS power will be low (er) due to the duty - strob looks like a short when pulse on - 1u acts as a tank cap and dumps some of its charge into the strobe then gets recharged by the 100Ohm.

Transformer just there to boost a 5V pulse to a voltage level needed to engage the lamp.

22pf acts to AC couple the 1kHz pulse to the XFMR. 10nF used to produced a rounded profile to the pulse comming through the 10pF (possibly more use???), current flowing though the primary winding then goes through 110Ohm res at the BJT base and turns it on and tehn AC couples teh primary winding to GND discharging the XFMR.

I am probably wrong but a first guess.

 

[Ali Sajjad]

Wat i guess is that the 10nF capaciot charges through the 1100 ohm resistence (1k + 100 ohm). When the input pulse goes high, the transitor starts to pass current between Collector and Emitter ( acts as a short circuit), so that the 10nF capacitor discharges rapidly through the transistor therby producing a trigger pulse to the XFMR and the XFMR outputs a high voltage spike that triggers the xenon lamp. The 22pF capacitor just acts to decouple the DC voltage, and allows only sudden discharge of 10nF capacitor.

This might be the whole story, ... but might not be

- Ali Sajjad