Emergency strobe flasher generates 250V

Posted on Apr 20, 2012

Figure 1 shows a complete circuit for an emergency lamp that operates from a 12V automotive battery. The xenon flash tube requires a 250V-dc anode voltage and a 4-kV trigger pulse. To generate the 250V dc, IC1, a switching regulator controller, and T1, a standard Versa-PAC transformer, operate in the discontinuous-flyback mode. With this configuration, circuit efficiency is typically 75 to 80%. R1 and IC1`s internal-sense-threshold voltage limit the peak primary current to 1.6A. The R2/R3 divider and IC1`s internal 1.25V reference at the VFB Pin determine the maximum-voltage setpoint. To generate the 4-kV trigger pulse, a standard cold-cathode- fluorescent-lamp (CCFL) backlight transformer, T2, operates in the forward mode. IC2, a dual MOSFET driver, functions as a 1-Hz oscillator and a one-shot for the trigger pulse for Q2.

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