| 摘要 |
<p>An electrical circuit (1) for an LED signal lamp,
comprising means for switching between a low level brightness, in particular a night time operation level brightness, and a high level brightness, in particular a daylight operation level brightness, of the LED signal lamp in dependence of an AC voltage at a voltage input (2) of the electrical circuit (1),is characterized in that the electrical circuit (1) comprises
- a full wave rectifier (3) for rectifying the AC voltage supplied at the voltage input (2) of the electrical circuit (1), thus providing a rectified AC voltage at two poles (4a, 4b), and
- at least one LED block circuit (5) connected to the poles (4a, 4b),
and that the LED block circuit (5) comprises
- an LED arrangement (6) comprising at least one light emitting diode,
- a comparator circuit (9) switching a signal voltage at a signal output (SO) of the comparator circuit (9) if the rectified AC voltage crosses a critical level (Vcrit),
- a switchable constant current source (7), with its switching input (SI1) connected to the signal output (SO) of the comparator circuit (9), wherein the switchable constant current source (7) is connected in series with the LED arrangement (6),
- and a switchable resistance (13), with its switching input (SI2) connected to the signal output (SO) of the comparator circuit (9),
wherein the comparator circuit (9), the switchable resistance (13) and the switchable constant current source (7) together with the LED arrangement (6) are connected in parallel at the poles (4a, 4b). The invention provides an electrical circuit for an LED signal lamp, suitable for control with a conventional railway control center, which is less susceptible to tolerances and temperature fluctuations and allows a better control over the LED brightness.</p> |
