Technik und Service
Seite: 34
Technology and Service
Page: 34
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
3.3. Flash triggering with ignition support:
Ignition support:
Capacitor C102 is charged to the flash-capacitor voltage V
C001
= 330 V via R101 and R103. To trigger the
flash, the IGBT Tr401 is switched on with a positive (+17 V) pulse on its gate. This causes capacitor C102 to
be discharged via R102. The resulting current generates a short negative voltage pulse (ignition-support pulse)
equal to the flash-capacitor voltage V
C001
= -330 V across R102.
This negative ignition-support pulse is connected via R103 to the cathode of the flash tube Roe001 (which is
connected to the anode of D101). Since the anode of flash tube Roe001 is connected to the positive potential
of the flash-capacitor voltage V
C001
= 330 V, the potential difference between the anode and cathode of
Roe001 is equal to twice the flash-capacitor voltage (or about 660 V). This makes it easier to ignite the flash
tube.
Ignition pulse:
The ignition capacitor C101 is charged via resistor R101 and the primary winding of the ignition coil to the
flash-capacitor voltage V
C001
= 330 V. When the IGBT Tr401 conducts, the ignition capacitor is discharged
rapidly through the primary winding of the ignition coil T101. This induces a voltage pulse (ignition pulse) of
about 8 kV to 10 kV in the secondary winding of the ignition coil, and this is connected to the conductive
coating of the flash tube The flash tube ignites and the flash capacitor is discharged by the flash current
through the flash tube.
4. Flash light control:
4.1. Control in manual flash mode (M or Mlo):
In manual flash mode M or Mlo, the flash may not be switched off by a TTL pulse from the camera. In order to
ensure that such a TTL pulse has no effect, the µC IC401 switches pin 34 (TTL_GATE) to LOW in manual flash
mode. The IGBT Tr401 is then controlled only by the level at pin 53 (IGBT-DRIVE) des µC IC401.
4.2. Control in TTL flash mode:
A few microseconds after the SYN time, µC IC401 switches pin 53 (IGBT-DRIVE) to HIGH. At this time, the
signals TTL-GATE and TTL pulse are LOW and the output of circuit IC406B (pin 4) is HIGH. IGBT Tr401
conducts and the flash is triggered. About 4µs later, µC IC401 switches pin 34 (TTL_GATE) to HIGH and thus
opens the TTL gate. IGBT Tr401 continues to conduct. If a TTL pulse arrives within the next 3.3 ms (TTL gate
time), the IGBT cuts off and the flash is extinguished. At the end of the TTL gate time, µC IC401 switches pin
34 (TTL_GATE) back to LOW. Any TTL pulse which arrives after this has no effect and the IGBT Tr401
continues to conduct.
