© 2000 Fairchild Semiconductor Corporation

www.fairchildsemi.com

KA2803B • Rev. 1.0.7

2

Block Diagram

Figure 1. Block Diagram

Application Circuit

Figure 2.

Full-Wave Application Circuit

Figure 3.

Half-Wave Application Circuit

Application Information

(Refer to full-wave application circuit in Figure 2)

Figure 2 shows the KA2803B connected in a typical

leakage current detector system. The power is applied

recommended above 1µF.

If the leakage current is at the load, it is detected by the

zero current transformer (ZCT). The output voltage

signal of ZCT is amplified by the differential amplifier of

the KA2803B internal circuit and appears as a half-cycle

sine wave signal referred to input signal at the output of

the amplifier. The amplifier closed-loop gain is fixed

about 1000 times with internal feedback resistor to

compensate

for

zero

current

transformer

(ZCT)

the breaker satisfies the required sensing current. The

current is injected at the breaker; this resistor should be

used

to

protect

the

earth

leakage

detector

IC

to several k.

canceller capacitance, but it is not usually used.

When high noise is present, a 0.047µF capacitor may be

connected between Pins 6 and 7. The amplified signal

finally appears at the Pin 7 with pulse signal through the

internal latch circuit of the KA2803B. This signal drives

the gate of the external SCR, which energizes the trip

coil, which opens the circuit breaker. The trip time of the

breaker

is

determined

by

capacitor

mechanism breaker. This capacitor should be selected

under 1µF to satisfy the required trip time. The full-wave

bridge supplies power to the KA2803B during both the

positive and negative half cycles of the line voltage. This

allows the hot and neutral lines to be interchanged.