Line Voltage Detector Circuit - Star Micronics TSP400 Series Technical Manual

THEORY OF OPERATION
2-5. +5V Line Voltage Detector Circuit
The voltage-detection IC (IC4 in Fig. 2-10) detects momentary drops or unstable levels in the +5V line voltage. IC4
operation is illustrated by the equivalence circuit shown below.
Fig. 2-11 shows the operational timing. If the +5V line voltage falls below 4.25V, the IC produces a reset signal at its
OUTPUT terminal, resetting the CPU and the gate array.
V
CC
1
S A typ
R1
–
+
R2
1.25V
3
GND
Fig. 2-11 Equivalence Circuit for Voltage Detecting IC
V Voltage
CC
4.25V
0.8V
Output
Voltage
Fig. 2-12 Operation Timing Chart
5
–
4
Cd
td td
td = 0.34 Cd (pF) [ s]
– 28 –
OUT
t
t