Metz mecablitz 44 MZ-2 Servicehandbuch Seite 33

Technik und Service Seite: 33
Technology and Service Page: 33
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
IGBT conducting (pin 4 HIGH):
With a HIGH potential at pin 4 of IC406B, the base of Tr405 is driven via the RC circuit R4007/C412 and
Tr405 conducts. This connects the base of Tr404 to ground via R4005 and Tr404 also conducts. At this time,
Tr420 is already cut off due to the drive signal from the second path. The base of Tr402 is driven with a signal
from the +17 V supply voltage via R4002. Tr402 conducts. The base of Tr403 no longer receives a drive
voltage and Tr403 cuts off.
The output of the push-pull circuit with Tr402 and Tr403 is HIGH. The gate of the IGBT Tr401 thus receives a
drive signal and the IGBT Tr401 conducts.
The simultaneous use of two circuit paths to drive the push-pull circuit Tr402/Tr403 ensures that the output
signal from this circuit has steep edges and that the IGBT Tr401 switches with the necessary speed.
D402 acts as a suppressor diode to prevent the dangerous flash-capacitor voltage from reaching the low-
voltage parts of the flash unit (or to limit it to a maximum of 33 V) in the case of a short-circuit in the IGBT
Tr401. R4001 limits the gate current of the IGBT Tr401 to about 0.7 A when the IGBT is driven.
D401 acts as a recovery diode for the inductances in the flash-current circuit and suppresses voltage spikes
which may occur when the IGBT Tr401 cuts off.
IGBT drive logic:
The switching state of the IGBT Tr401 depends on the level at the output (IC406B, pin 4) of the gate logic for
the IGBT drive signal. IGBT Tr401 conducts if there is a HIGH level at the output of the gate logic. The three
inputs to the gate logic are µC IC401, pin 53 (IGBT-DRIVE), µC IC401, pin 34 (TTL_GATE) and IC406D, pin
13 (TTL pulse).
TTL-Impuls = TTL pulse
Treiberstufe = Driver stage