Fairchild Semiconductor RV4140A Datasheet

RV4140A

Low Power Two-Wire Ground Fault Interrupter Controller

www.fairchildsemi.com

Features

• Powered from the AC line

• Built-in bridge rectiﬁer

• Direct interface to SCR

• 350 mA quiescent current

• Adjustable trip current

• Adjustable time delay

• Minimum external components

• Meets UL 943 requirements

• Speciﬁcally for two-wire systems

• For use with 110V or 220V systems

Description

The RV4140A is a low power controller for AC outlet appliance leakage circuit interrupters. These devices detect hazardous current paths to ground such as an appliance falling into water. The interrupter then open circuits the line before a harmful or lethal shock occurs.

Internally, the RV4140A has a diode bridge rectiﬁer, zener shunt regulator, op amp, current reference, time delay circuit, latch and SCR driver.

An external sense transformer, SCR, relay, two resistors and three capacitors complete the design of the circuit interrupter. The simple layout and minimum component count ensure ease of application and long term reliability.

Block Diagram

RV4140A

Latch

4.7K

Delay

65-4140A-01

Rev. 1.0.0

RV4140A PRODUCT SPECIFICATION

Functional Description

(Refer to Block Diagram and Figure 1 )

The shunt regulator generated by a 6.5V zener diode is built into the internal bridge rectiﬁer. It is divided to create an internal reference voltage of 2.9V connected to pin 3. The secondary of the sense transformer is AC coupled to the inverting input of the sense ampliﬁer at pin 2; the non-inverting input is referenced to pin 3. A current feedback loop around the sense ampliﬁer ensures a virtual ground will be presented to the secondary of the sense transformer. In this manner it acts as a current transformer instead of a voltage transformer. In this mode, the transformer’s characteristics are very predictable and circuit adjustments are not necessary in production.

The sense transformer has a toroidal core made of laminated steel rings or solid ferrite material. The secondary of the transformer is 500 to 1000 turns of #40 wire wound through the toroid. The primary’s one turn made by passing the AC hot and neutral wires through the center of the toroid. When a ground fault exists, a difference exists between the current ﬂowing in hot and neutral wires. The difference primary current, divided by the number of secondary turns, ﬂows through the secondary wire of the transformer.

The AC coupled transformer secondary current then ﬂows through the sense ampliﬁer’s feedback loop, creating a full wave rectiﬁed version of the secondary fault current. This current passes through R equal to R sense transformer turns ratio. This voltage is compared with the reference voltage at pin 3.

If the voltage at pin 1 is greater than pin 3, a comparator will charge C2 through a 29 mA current source at pin 8. If the voltage at pin 1 exceeds pin 3 for longer than the delay time, a 400 mA current will pulse between pins 7 and 6 which will trigger the gate of the SCR.

If the voltage at pin 1 exceeds pin 3 for less than the delay time, the SCR will not trigger.

The fault current at which the controller triggers the SCR is dependent on the value of R determined by C2.

times the peak fault current divided by the

SET

at pin 1, generating a voltage

SET

and the time delay

SET

Supply Current Requirements

The RV4140A has a built-in diode bridge rectiﬁer that provides power to the chip independent of the polarity of the A C line. This eliminates the external rectiﬁer required for previous GFCI controllers.

limits the shunt regulator current to 2 mA. The rec-

LlNE

ommended value is 47K to 91K for 110V systems and 91K to 150K for 220V systems. The recommended maximum peak line current through R

DO NOT connect a ﬁlter capacitor between pins 5 and 6 in an attempt to ﬁlter the supply voltage at the RV4140A. Proper operaton of the R V4140A requires the internal supply voltage to be unﬁltered.

LlNE

is 7 mA.

SCR Driver

The SCR must have a high dV/dt rating to ensure that line noise (generated by electrically noisy appliances) does not falsely trigger the SCR. Also, the SCR must ha ve a gate dri ve requirement less than 200 mA. C3 is a noise ﬁlter that prevents high frequency line pulses from triggering the SCR.

The relay solenoid used should have a 3 ms or less response time to meet the UL 943 timing requirement.

Supplier of Sense Transformers and Cores

Magnetic Metals Corporation, Camden, NJ 08101, (609) 964-7842, supplies a full line of ring cores and transformers designed speciﬁcally for GFCI and related applications.

Determining the Values of RSET and C2

Determine the ground fault trip current requirement. This will be typically 5 mA in North America (117 VAC) and 10 mA in the UK and Europe.

Determine the minimum amount of time delay required to prevent nuisance tripping. This will typically be 1 to 2 ms.

The value of C2 required to provide the desired delay time is:

C2 = 10 x T

where C2 is in nF, and T is the desired delay time in ms.

UL 943 requires the circuit interrupter trip when the ground fault exceeds 6 mA and not trip when the fault current is less than 4 mA.

PRODUCT SPECIFICATION RV4140A

The value of R

to meet nominal ground fault tip current

SET

speciﬁcation is:

SET

---------------------------------------------------------------= I

FAULT

2.05 N´ COS 180´ TP¤()

Where:

•R

SET

is in kW

• T is the time delay in ms

• P is the period of the line frequency in ms

•I

is the desired ground fault trip current in mA

FAULT

RMS.

• N is the number of sense transformer secondary turns.

Sense Transformer

Mov

Line

1:500 Turns Ratio 3 Ring Steel Core

10 F

0.1 F

Hot

Neutral

SET

191K

1 2 3 4

0.02 F

RV4140A

This formula assumes an ideal sense transformer is used. The calculated value of R

may have to be changed up to

SET

30% when using a non-ideal transformer.

TEST

15K

8 7 6 5

Press to Test

Normally Latching

Solinoid

Closed

Contacts

Tag

X0103DA

10 nF

LINE

91K

Load

65-4140A-02

Figure 1. Appliance Leakage Detector Circuit Application

RV4140A PRODUCT SPECIFICATION

Pin Assignments

PDIP

(Top View)

SOIC

(Top View)

SET

VFB

2.9V

Ground 5

C Delay

SCR Trigger

Neutral Line

SET

VFB

2.9V

Ground 5

65-4140A-03

C Delay

SCR Trigger

Neutral

Line

Absolute Maximum Ratings

Parameter Min. Typ. Max. Units

Supply Current 7mA Internal Power Dissipation 500 mW Storage Temperature Range -65 +150 °C Operating Temperature Range -35 +80 °C Lead Soldering Temperature 60 Seconds, DIP +300 °C

10 Seconds, SOIC +260 °C

Thermal Characteristics

Parameter 8 Lead Plastic SOIC 8 Lead Plastic DIP

Maximum Junction Temperature +125°C +125°C Maximum P Thermal Resistance, q For TA > 50°C Derate at 4.1 mW/°C 6.25 mW/°C

<50°C 300 mW 468 mW

DTA

240°C/W 160°C/W

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