Technik und Service
Seite: 34
Technology and Service
Page: 34
mecablitz 40 MZ-2
ENGLISH
As soon as batteries are fitted, IC502 receives voltage via fuse resistor R501, fuse Si501 and diode
D513. In addition to the regulated voltage at pin 1, IC502 generates a reset signal at pin 4. A low
signal at pin 2 resets IC504.
Clock supply:
The 6 MHz clock signal of the microprocessor IC301 is decoupled from IC301 by the single inverter
IC303 and is connected via R342 to pin 7 of the ASIC IC504. Resistor R342 limits the charging current
of the parasitic capacitances during the steep edges of the clock signal (squarewave signal) and
thus reduces any interference this could cause. A clock divider within IC504 derives the basic 1 MHz
clock signal from the 6 MHz signal, and this basic clock signal is used for all internal stages of the
ASIC. The division ratio of this clock divider can be set with the jumper R557 at pin 9 of IC504 to
either 6:1 (high) or 4:1 (low). At the moment, this jumper is set for a division ratio of 6:1.
ASIC bus:
(see "Microprocessor and periphery", page 29)
Control of the main converter:
The main converter is controlled via pin 43 of IC504, which can be set and reset via the serial
interface by IC301. A low signal at this pin means "main converter off", and a high signal means
"main converter on". The control of the main converter via pin 43 is also affected via pin 1 of IC504
by the Schmitt trigger with Tr511 and Tr512. The two signals, from IC301 and from the Schmitt trigger,
are ANDed together, which means that pin 43 is switched to high only if both of these signals
request "converter on".
If the flash capacitor is fully discharged, the main converter places such a load on the battery that
correct operation of the auxiliary converter cannot be guaranteed. The Schmitt trigger Tr511/Tr512
monitors the supply voltage of the auxiliary converter: if this voltage drops below 2.3V, the Schmitt
trigger sends a low signal to pin 1 of IC504 to switch off the main converter. As soon as the supply
voltage rises above 3V, the main converter is switched on again.
Control of the auxiliary converter:
IC301 can set and reset pin 42 of IC504 via the serial interface in order to switch the auxiliary
converter on and off. A low signal at pin 42 means "auxiliary converter off", and a high signal
means "auxiliary converter on".
Ignition pulse generation:
A low-high transition at pin 3 of IC504 (internal sync signal from pin 49 of IC301) causes the ignition
pulse generator to generate a squarewave pulse with a width of 32 µs at pin 35. This pulse triggers
the ignition thyristor Ty401 via transistor Tr509 and thus ignites the flash tube.
IGBT control:
