Detection of a hazard condition of a load
An electrical circuit is described for detection of an electrical hazard condition of a load 20 , in particular of an OLED lighting element comprising driving terminals A, C. An electrical hazard condition, such as an overvoltage or short circuit is to be detected between terminals 22 a, 22 b of the circuit. A disabling element 24 is connected to one of the terminals 22 a, 22 b to disable the load. A monitoring circuit is connected to monitor a voltage V or current magnitude at at least one of the terminals 22 a, 22 b . The monitoring circuit comprises a maximum or minimum value detector 26 to deliver a maximum or minimum value V max of the voltage or current magnitude over time. The monitoring circuit is disposed to monitor the maximum or minimum value V max to detect the electrical hazard condition. A monitoring circuit is connected to activate the disabling element 24 if an electrical hazard condition is detected. The electrical circuit, a lighting arrangement including an LED or OLED lighting element and the electrical circuit, and a detection method allows to operate a load with different types of power supply, in particular also by PWM.
1. An electrical circuit for detection of a short circuit or overvoltage or both condition(s) of a load, comprising:
a power source delivering a gapped electrical power supply which is a regulated current that is time-modulated such that the electrical power is supplied intermittently in a first time interval of constant current amplitude whereas no electrical current is supplied in a second time interval following the first interval,
terminals for said load between which the short circuit or overvoltage or both condition(s) are to be detected,
a disabling element connected to at least one of said terminals to disable said load,
a monitoring circuit connected to monitor a voltage or current magnitude at least one of said terminals to detect the short circuit or overvoltage or both condition(s),
said monitoring circuit comprising a maximum or minimum value detector to deliver a maximum or minimum value of said voltage or current magnitude over a time at least longer than the second time interval in the power supply, such that said monitoring circuit is disposed to monitor said maximum or minimum value over the time to detect the short circuit or overvoltage or both condition(s), and
wherein said monitoring circuit is connected to activate said disabling element when the short circuit or overvoltage or both condition(s) are detected.
2. The electrical circuit according to claim 1 , where said disabling element is a controllable switching element connected between said terminals, and said monitoring circuit is connected to close said switching element if the short circuit or overvoltage or both condition(s) are detected.
3. The electrical circuit according to claim 1 , where said monitoring circuit further comprises a delay timer circuit for providing an activation signal when a detection signal is applied to said delay timer circuit for a delay time interval, and said delay timer circuit is connected to supply said activation signal to said disabling element.
4. The electrical circuit according to claim 1 , where at least one electrical energy storage element is connected to at least one of said terminals to receive and store electrical energy, and where at least said monitoring circuit is connected to be supplied with electrical energy from said electrical energy storage element when no electrical energy is supplied at said terminals.
5. The electrical circuit according to claim 1 , where said monitoring circuit comprises at least a comparator circuit to compare said maximum or minimum value of said voltage or current magnitude over time at least longer than the second time interval to a threshold value.
6. The electrical circuit according to claim 5 , where said monitoring circuit comprises at least a first comparator circuit to compare said maximum or minimum value of said voltage or current magnitude over time at least longer than the second time interval to a lower threshold value and a second comparator circuit to compare said maximum or minimum value of said voltage or current magnitude over time at least longer than the second time interval to an upper threshold value.
7. A lighting arrangement including at least one LED or OLED lighting element comprising driving terminals and an electrical circuit according to claim 1 connected in parallel to said driving terminals.
8. The electrical circuit of claim 1 where the time modulated current of the gapped electrical power supply from the power source is modulated by pulse width modulation (PWM).
9. The electrical circuit of claim 1 where the load is an OLED device.
10. A method of detection of a short circuit or overvoltage or both condition(s) between terminals of a load in an electrical circuit, comprising the steps of:
providing a power source delivering a gapped electrical power supply which is a regulated current that is time-modulated such that the electrical power is supplied intermittently in a first time interval of constant current amplitude whereas no electrical current is supplied in a second time interval following the first intervals,
monitoring a voltage or current magnitude at least one of said terminals and controlling a disabling element connected to at least one of said terminals to disable said load in case of the short circuit or overvoltage or both condition(s),
wherein said monitoring step includes detecting a maximum or minimum value of said voltage or current magnitude over a time at least longer than the second interval in the power supply, and monitoring said maximum or minimum value to detect the short circuit or overvoltage or both condition(s) over the time, and activating said disabling element when the short circuit or overvoltage or both condition(s) are detected.