Hitachi RAS-25CNH2 Service Manual page 61

9. Trip Signal Synthesis Circuit
Fig. 9-1 shows the trip signal synthesis circuit.
G
This circuit uses the upper and lower arm transistor drive signals to modulate the chopper signal or stops
the drive signal, according to the presence or absence of the Ip cut signal and reset signal.
R7
Q1
0V
8J-HIC
Table 9-1 shows the circuits to which the modulated signals are transferred.
G
For example, the chopper signal is transferred only to the upper arm transistor drive circuit, and the reset
signal is transferred to the microcomputer and upper and lower arm transistor drive circuits.
e i
Pins of the micro computer change from "Lo" to "Hi" alternately and supply signals to PQ2-PQ7.
G
The chopper signal from the micro computer is inverted by Q307, and turns on or off PQ2-PQ4, to which
G
voltage is supplied, with high frequencies, to let current flow to them to transfer the upper arm drive signal.
When the reset voltage is "Lo", the current operating PQ5-P07 is stopped, and the lower arm transistor
G
drive signal is turned off.
The peak current cut off (Ip cut off) signal fixes the voltage at upper and lower arm drive circuits to "Lo"
G
via D301 and D304, and turns off the drive signal in the same way as when the reset signal is "Lo".
Table 9-1 Circuits to which trip signals are transferred
Modulated signals
Chopper signal
Start current limit signal
Peak current cut off signal
Reset signal
Reset circuit
Ip
71
Chopper
I
0V
D304
23
24
25
26
27
28
Fig. 9-1 Trip Signal Synthesis Circuit
Circuit
Microcomputer
5V
Q304
5V
R315
0V
D301 D305
5V
Q306
Q307
5V
0V
Upper arm transistor
––––
––––
– 64 –
12
5
PQ2
6
PQ3
7
PQ4
8
PQ5
9
PQ6
10
PQ7
11
Lower arm transistor
drive circuit
Upper
arm
drive
Lower
arm
drive
drive circuit
––––
––––