BINARY LOW VOLTAGE GLOW PROTECTION (LVGP) CIRCUIT FOR LED INDICATORS

Binay's patented LVGP Circuit provides protection from false indications at leakage voltages in industrial environments

Light emitting Diodes (LEDs) offer the advantages of long life, low power consumption and resistance to vibration and shock. However, they also possess certain drawbacks, and the proper design of an LED Module Pilot Light requires appropriate modifi-cations in order to obviate the negative effects of such characteristics.

One such effect relates to the characteristic of an LED which causes it to glow at very low voltages and currents. Whereas the thermal inertia of the filament prevents a filament bulb from glowing if the applied voltage is less than 25% of the rated voltage of the bulb, the LED is current sensitive and begins glowing at very low currents of 1mA to 2mA.

Electric conventions normally dictate that proper earthing be provided so that residual voltages and currents are eliminated in cable lines. However, where earthing is has not been properly effected and there are long runs of parallel cables (as in in-dustrial environments), leakage voltages are gener-ated due to capacitive/inductive effects. Spurious voltages of 10V, 20V, 30V, or even 60 to 100V have been reported. Moreover in some circuits, the neu-tral line may be floating (for example, in logic cir-cuits). Such induced voltages may cause the LEDs to give a slight glow which is perceptible, thus giving a false indication.

Binay has designed a patented Voltage Blocking Circuit to block these spurious voltages, and allow current to pass only above a specified voltage. This circuit - known as the Binay Low Voltage Glow Protection (LVGP) Circuit - is provided as stan-dard in all our Industrial Series LED Modules (110V and 230VAC types), and blocks all leakage voltages below 25 volts AC.

We recommend that our industrial users specify In-dustrial Series LED Modules for all their installa-tions. The Industrial Series LED Module incorpo-rates this 25VAC LVGP Circuit integrally on a printed circuit board.

(N.B. Our LED Modules are labelled as rated voltage 25%. This is only to indicate that useful light emission, as specified in the specification, will be available up to minimum 25%. This does not mean that it will not nor-mally glow below the rated voltage; that is, unless the LVGP Circuit is provided, as in the Industrial Series.)

As stated, this voltage will protect the LED indicator in case of leakage voltages up to 25VAC. Should a higher leakage voltage be encountered, an LVGP Circuit of the appropriate higher voltage should be specified.

Discrete LVGP Units can also be attached sepa-rately (externally) to existing LED Modules. This is a small add-on unit, having dimensions of about 25mm (length) x 7mm (diameter). The Unit at-taches to the terminals of the LED Module; termi-nals are provided for input cable termination. How-ever, power consumption increases when this cir-cuit is incorporated externally.

LVGP Units for DC circuits have different circuitry.

External LVGP Units are available as follows:

LVGP Type Blocks leakage voltages up to
LVGP 25VAC
LVGP 50VAC
LVGP 75VAC
LVGP 100VAC
LVGP 125VAC
25VAC
50VAC
75VAC
100VAC
125VAC