Star Micronics TSP400 technical manual +5V Line Voltage Detector Circuit

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.

R1

R2

1.25V

VCC

1

S∝A typ

–

+

3

GND

–

4

Cd

5

OUT

Fig. 2-11 Equivalence Circuit for Voltage Detecting IC

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.

VCC Voltage
4.25V
0.8V	t
Output
Voltage
td	td
	t
	td = 0.34 × Cd (pF) [∝s]

Fig. 2-12 Operation Timing Chart

– 28 –