EP2124507A2 - Signal issuer for an LED light signal - Google Patents

Abstract

The transmitter has a circuit part provided for adjusting a signal transmitter current-operating voltage-characteristic curve of a LED-light signal to a characteristics curve of a filament lamp-light signal. A load is controlled based on the operating voltage, where a resistor network with electronically switchable resistors (R1-R3) is provided as the load. Electronic switches (13.1-13.3) of the resistor network are controlled by a microcontroller (14) based on the operating voltage, and an opening-contact is provided for simulation of switching current surge of the lamp-light signal.

Description

The invention relates to a signal generator for a LED light signal with a circuit part for adapting a signal generator current operating voltage characteristic of the LED light signal to a characteristic of a light bulb light signal, wherein a load in response to the operating voltage can be controlled.

Light signals or LEDs on the basis of LEDs - light emitting diodes - instead of incandescent lamps are increasingly being used in many areas, especially in signaling technology. LEDs are comparatively inexpensive, durable and bright. However, the use of LEDs is difficult where the incandescent lamps are to be replaced by LEDs without changes to an existing monitoring device. This is particularly true for light signal circuits of the railroad, in which the proper function is usually monitored by a safe signaling by means of a signal-wise control part. In order to continue to use this monitoring device without modification, the signal generator current operating voltage characteristic of the LED light signal must be approximately matched to that of the incandescent light signal. In order to achieve interface compatibility, therefore, the additional circuit part in the signal generator is required. This circuit part allows the characteristic adjustment by the difference between the power consumption of the illuminated LEDs and the replaced light bulb is compensated by a corresponding electrical power consumption.

Another special feature of railway light signals is the signaling outside of tunnels or environmental conditions with almost constant light conditions. In terms of circuitry, this is a reduction in the light output, ie the operating voltage, for night operation compared to daytime operation. This results in the need for the most accurate adjustment of the characteristic not only punctually, but over wide ranges of the operating voltage.

From the EP 1 232 654 A1 is an adaptive characteristic adaptation for LED signal generator, in accordance with FIG. 1 from the operating voltage, a control voltage is derived. In this designed for AC operation circuit, a rectifier bridge GR is connected in parallel with a control circuit 1 for a load 2, consisting of transistors T1, T2 and load resistors RL1, RL2 and current diodes D1 and D2. The control circuit 1 generates from the operating voltage a control voltage which sets the average current flow through the transistors T1 and T2. The characteristic curve adaptation achievable in this way is relatively inaccurate. The load current, which results mainly through the transistors T1 and T2 is not sinusoidal at sinusoidal operating voltage, whereby the desired purely resistive character of the light bulb to be simulated can not be replicated exactly. To make matters worse, that the value of the non-sinusoidal load current is dependent on the measurement method in the light-bulb-specific monitoring device of the control unit-side actuating part. In practice, quite different current measurement methods are used, resulting in considerable measurement and interpretation uncertainties. As a result, the design and verification of this known circuit arrangement for characteristic adaptation is problematic.

It is also conceivable, instead of the transistor combination according to FIG. 1 a pulse width modulated electronic switch 3rd according to FIG. 2 to use. The circuit comprises, in addition to a power supply 4, an operating voltage measurement 5, wherein a pulse width modulation - PWM - is generated from the operating voltage by means of an algorithm 6, which activates the electronic switch 3 for energizing a load resistor 7. With a sinusoidal variation of the pulse / pause ratio of the PWM over the half sine waves, an approximately resistive current / voltage curve can also be simulated. The disadvantage, however, is that due to the steep switching edges of the PWM high-frequency interference on the supply line, which problems with respect to the electromagnetic compatibility - EMC - produce, which in turn can only be controlled by consuming network filter 8. As a result, the overall circuit is very complex in terms of design and implementation.

In a further modification of the above EP 1 233 654 B1 known and in FIG. 1 illustrated basic principle serves as an electronically controllable load according to FIG. 3 the DS path of a power MOSFET 9. The DS resistor, which is intended to produce the desired power loss 10 for characteristic adjustment, depends on the DC voltage, but also on the DS voltage. This results in a non-linear, not purely ohmic relationship, which must be complexly compensated circuitry. In addition, the DS resistance is also highly dependent on the temperature and the specimen of the power MOSFET 9. This in turn increases the complexity of a MOSFET drive circuit 11 to simulate a purely resistive load. Via a feedback 12, the desired current must be monitored in order to track the gate voltage continuously. Ultimately, the MOSFET variant for use for characteristic adaptation, in particular for AC voltage, requires an impractical large-scale circuit complexity.

The invention has for its object to overcome these drawbacks and to provide a signal generator of the generic type, which allows a simple way a characteristic adjustment according to needs accuracy.

According to the invention the object is achieved in that a resistor network with electronically switchable resistors is provided as the load. By using electronically switchable resistors, in contrast to the known transistor variant and its modifications by means of PWM or MOSFET, a purely ohmic load character is generated. For resistors, there is a strictly linear relationship between current and voltage according to ohmic law I = U / R. Signal distortions in the zero crossing of the load current or harmonics do not occur. The control of the resistors by means of electronic switches made possible by operating voltage-dependent connection or disconnection of resistors in a simple manner, a realization of the desired load for the characteristic adjustment.

Although continuous adjustment of the desired load resistance is not possible with resistor networks, it is also not absolutely necessary. Within acceptable tolerance limits meet only a few switched resistors, so that ultimately a cost-effective implementation is possible. Another advantage is the expected long-term stable behavior even with significant temperature fluctuations.

According to claim 2, it is provided that the electronic switches of the resistor network can be driven by a microcontroller, depending on the operating voltage. Thus, it is easily possible, depending on the measured operating voltage a specific To generate bit pattern for the control of the electronic switch.

The resistor network may additionally be equipped according to claim 3 with at least one normally closed contact for simulating an inrush current of the incandescent light signal. The normally closed contact is preferably in the ground state, i. H. with dark signal, closed. After switching on the operating voltage, the normally closed contact is opened after a specified time. This results shortly after switching on the operating voltage for a short time an additional surge, which simulates the surge, which arises at the incandescent light signal due to its lower resistance in the cold state. Since the inrush current in the incandescent light signal depends on the magnitude of the applied voltage and on the heating of the filament, which leads to an increase in the resistance, also on the time, the accuracy of the replica by the use of multiple break contacts, the be controlled according to these initial conditions can be improved.

Figur 1

eine bekannte Schaltungsanordnung zur Anpassung einer Signalgeberstrom-Betriebsspannungs-Kennlinie eines LED-Lichtsignals,

Figur 2

eine erste Abwandlung der Kennlinienanpassung gemäß Figur 1 in schematisierter Darstellung,

Figur 3

eine zweite Abwandlung der Kennlinienanpassung gemäß Figur 1 in schematisierter Darstellung,

Figur 4

eine erfindungsgemäße Kennlinienanpassung in der Darstellungsweise der Figuren 2 und 3,

Figur 5

ein Signalgeberstrom-Betriebsspannungs-Diagramm und

Figur 6

vier Varianten eines Widerstandsnetzwerkes.

The invention will be explained in more detail with reference to figurative representations. Show it:

FIG. 1

a known circuit arrangement for adapting a signal generator current operating voltage characteristic of an LED light signal,

FIG. 2

a first modification of the characteristic adaptation according to FIG. 1 in a schematic representation,

FIG. 3

a second modification of the characteristic adaptation according to FIG. 1 in a schematic representation,

FIG. 4

a characteristic adaptation according to the invention in the representation of the Figures 2 and 3 .

FIG. 5

a buzzer current operating voltage diagram and

FIG. 6

four variants of a resistor network.

The above-explained known characteristic adaptation according to FIG. 1 and their in the Figures 2 and 3 illustrated modifications have the particular disadvantage that a purely resistive load character is not or only with very considerable circuit complexity can be achieved.

FIG. 4 shows the essential components of a characteristic adaptation according to the invention. Instead of transistors - FIG. 1 - or PWM - FIG. 2 - or MOSFET - FIG. 3 - A resistor network with resistors R1, R2, R3, which are controlled by electronic switches 13.1, 13.2, 13.3, used. The desired load is realized by operating voltage-dependent connection or disconnection of the resistors R1, R2, R3. The circuit arrangement of the resistors R1, R2, R3, which may also have different values, is freely configurable according to the respective requirements. For controlling the electronic switches 13.1, 13.2, 13.3 is preferably a microcontroller 14 or a programmable logic.

FIG. 5 illustrates a signal generator power operating voltage diagram in which the characteristic 15 to be emulated of a light bulb, the characteristic 16 of an LED array and the characteristic curve 17 of a matching circuit according to the principle of FIG. 4 are shown. It can be seen that a very good characteristic curve adaptation already results with only five resistance levels. The frequency of the characteristic 17 can be by the freely selectable number of resistors R1 to R7 used according to FIG. 6 within the scope of the monitoring-specific tolerances.

The LED characteristic 16 is split into a night area <8 V and a day area> 8 V. Especially in the night area, there is a big difference between the power consumption of the incandescent lamp and the power consumption necessary for the illumination of the LEDs. By the claimed circuit, the signal generator generates in this critical area suitable for external monitoring output, which comes very close to the incandescent lamp.

The circuit can also be used to simulate the cold resistance of the signal lamp. For this purpose, according to FIG. 6 d, an opener contact 18 is provided which is closed when the signal is switched off. After switching on the operating voltage of the normally closed contact 18 is opened after a specified time. The resulting additional current flow shortly after switching on reflects the additional current flow, which arises in the case of an incandescent lamp due to its lower resistance in the cold state. Since the resistance of the filament increases as a function of the heating, the inrush current of the incandescent lamp depends on the level of the applied voltage and on the time. To replicate this relationship exactly, several separately controlled break contacts 18 can be used.

FIGS. 6a, 6b and 6c show resistor networks of various complexity which can be combined with the cold-thread simulation of FIG. 6d.

Claims (3)

Signal generator for a LED light signal with a circuit part for adapting a signal generator current operating voltage characteristic (16) of the LED light signal to a characteristic curve (15) of a light bulb light signal, wherein a load can be controlled as a function of the operating voltage,
characterized in that
as a load a resistor network with electronically switchable resistors (R1 to R7) is provided. Signaling device according to claim 1,
characterized in that
the electronic switches (13.1 to 13.6) of the resistor network operating voltage-dependent by means of a microcontroller (14) are controlled. Signaling device according to one of the preceding claims,
characterized in that
at least one normally closed contact (18) is provided for simulating an inrush current of the incandescent light signal.

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