Peak Current Cut Off Circuit And Waveforms At Each Section - Hitachi RAS-25CNH1 Service Manual

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Table of Contents

Peak current cut

off circuit

DC 260V

290V

Voltage amp.

circuit

Detection

resistor

R806

The following describes the operations of each circuit in detail.

(1) Peak current cut (Ip) off circuit

Fig.8-3 shows the Peak Current Cut off Circuit and Waveforms at Each Section.

DC current (ld)

18A

Voltage at point

0.9V

Micro computer

Voltage at pin

Voltage at point

Fig.

8 - 3

Ip cut off circuit detects an instantaneous large current and stops drive output signal to protect parts such

as power module, etc.

As shown in the figure, when current exceeding 18A flows, voltage at point A detected by detection

resistor is input to e terminal of COM (A). If it exceeds d terminal voltage, which is the set value, output

pin voltage (point B) of COM (A) changes from Lo to Hi. Thus, Q1 is turned ON to stop drive curcuit and,

at the same time, voltage at point C changes from Hi to Lo to send Ip signal to pin ™ of microcomputer

(observed by pin º of HIC) and microcomputer stops drive.

On the other hand, e terminal voltage is pulled up by R1, and DC current becomes 0A. Even when voltage

at point A returns to 0V, (power is not supplied - current value of zero), Output is temporarily held in Hi

state since voltage at - terminal is high. (memory function).

Just before drive signal is output the next time, Microcomputer switches pin £ from Hi to Lo (observed

by pin ⁄ of HIC), so that e terminal voltage < d terminal voltage to release memory function and return

to initial state.

Reset voltage

Reset circuit

Trip signal

synthesis circuit

Overload external

set value circuit

DC current level

POR

Micro

computer

AX-8E21

chopper