Guard circuit for the protection of capacitive loads

DETAILED DESCRIPTION Proceeding from the aforedefined state of prior art, the present invention is based on the problem of improving a guard circuit of the type described by way of introduction to the effect that a cost-effective miniaturization will be achieved while the anti-interference effect will be retrained.
This problem is solved by means of a guard circuit including a current detector means to detect the current flowing through the load and to emit a first blocking signal at least when the amount of the detected current exceeds a defined maximum value, a voltage detector means to detect the voltage applied in said supply network and to emit a second blocking signal when the amount of the detected voltage exceeds a defined maximum value, and a controllable switching means communicating with and under control of said current detector means and said voltage detector means so as to isolate the load from the supply network, with said controllable switching means isolating the load from the supply network when at least one of said first or second blocking signals is applied.
Whenever, a voltage pulse of the aforedescribed type will arise in the supply network initially the input current will undergo a rapid increase as a result of the capacitive load.
As soon as the input current will exceed the present maximum value the current is limited and therefore controlled.
As a result of this the input voltage now will increase more rapidly.
As soon as the input voltage will exceed the present maximum value the load is isolated from the network, which, as a result of the energy stored in the load, is not yet a complete disconnection of the energy supply for the load or the electronic device.
As soon as the load is disconnected from the network the voltage assumes the value defined by the network.
As soon as the voltage will drop again below the maximum value permissible for the load, which means that the interference pulse will thus cease to be dangerous, the load is reconnected to the network whereupon the "normal operation" is resumed