1. Field of the Invention
The present invention relates to a driving circuit for driving an electromagnetic relay having a coil and moving and fixed contacts.
2. Related Art
The main cause of abrasion of contacts in an electromagnetic relay is the bouncing of a moving contact (chattering between a moving contact and a fixed contact) occurring when the contacts are closed. When the contacts are closed, if the strength of magnetic field to attract the moving contact is controlled to gently rise so that the speed of the moving contact approaching the fixed contact becomes slow, the bouncing of the moving contact can be suppressed.
Conventionally, there are techniques to suppress the bouncing of the moving contact. According to one example of these techniques, the rising of magnetic field is caused to be slow as the result that the rising of coil current is made gentle due to large inductance of the coil. In another example a time constant circuit is provided with a driving circuit for an electromagnetic relay, and the rising of magnetic field is caused to be slow as the result that the rising of voltage applied to the coil is made gentle. The latter technique is disclosed in, for example, Examined Utility Model Publication No. S. 57-13700.
In the latter technique described above, the more gently the voltage applied to the coil is increased, the more effectively the bouncing of the moving contact can be reduced. It takes long time, on the other hand, for the coil-applied voltage to reach a starting voltage at which the moving contact starts to move. As a result, there arises a problem such that a response time for switching of the relay becomes long. In addition, because the coil-applied voltage at the time of the contacts being closed is apt to vary, there is another problem such that the bouncing of the moving contact can not be stably reduced.