Assessment of powering modes for DC-powered devices
A power-input stage ( 102 ) for a DC-powered device ( 100 ), the power-input stage including at least four pairs of power-input elements ( 104 ) for connecting to four pairs of external electrical conductors ( 106 ) for delivering DC power, and a powering-mode assessment unit ( 108 ) having a balance measurement stage ( 110 ) that is configured to perform a balance measurement for determining whether or not a first number of pairs of power-input elements, at which a positive power-supply voltage is available from the external electrical conductors, is equal to a second number of pairs of power-input elements, from which a negative power-supply voltage is available, and to provide a balance output signal indicative of a result of the balance measurement.
1. A power-input stage for a DC-powered device, the power-input stage comprising:
a connection unit comprising at least four pairs of power-input elements for connecting to the same number of at least four pairs of external electrical conductors for delivering DC power; and
a powering-mode assessment unit having a balance measurement stage that is configured to perform, before power is drawn for operation of the DC-powered device, a balance measurement for determining whether or not a first number of pairs of power-input elements, at which a positive power-supply voltage is available from the external electrical conductors, is equal to a second number of pairs of power-input elements, from which a negative power-supply voltage is available, and to provide a balance output signal indicative of a result of the balance measurement, wherein the balance measurement unit comprises two voltage dividers, each having a pair of inputs connected with a respective pair of power-input elements, and having respective center point taps, and a voltage sensor connected to the center point taps and configured to measure a center point voltage provided between the center point taps and a reference voltage and to provide the center point voltage as the balance output signal.
2. The power-input stage of claim 1 , wherein the powering-mode assessment unit further comprises a power-limit measurement stage which is configured to perform a power-limit measurement indicative of a maximum amount of DC power allowed for provision via the external electrical conductors and to provide a power output signal indicative of a result of the power-limit measurement.
3. The power-input stage of claim 2 , which is configured to perform the power-limit measurement only in case the balance output signal indicates that the first number is equal to the second number.
4. The input stage of claim 1 , wherein the power-limit measurement stage comprises:
a capacitance connected on its one side to the voltage sensor, and
a controllable switch for temporarily connecting the other side of the capacitance to a reference potential; wherein
the power-limit measurement stage is configured to determine the maximum amount of DC power allowed based on measuring a rate change of the of the center point voltage in response to connecting the capacitance to the reference potential.
5. The input stage of claim 1 , wherein the power-limit measurement stage comprises:
a measurement resistor connected on its one side to the voltage sensor, and
a controllable switch for temporarily connecting the other side of the measurement resistor to a reference potential, wherein the power-limit measurement stage is configured to determine the total amount of DC power available based on measuring the center point voltage in response to connecting the measurement resistor to the reference potential.
6. The input stage of claim 1 , wherein the voltage dividers of the balance measurement unit comprise diacs or an arrangement of Zener-diodes facing each other in series and respectively connected between the respective power-input element and the center point of the voltage divider.
7. A DC-powered device, comprising:
a power-input stage according to claim 1 ; and
a load unit, configured to receive DC power via the power-input stage in operation of the DC-powered device; and
a control unit configured to receive the balance output signal, and to determine and set an operating mode of the load unit in dependence on the balance output signal.
8. The DC-powered device according to claim 7 , wherein the control unit is configured to determine and set:
a first operating mode of the load unit requiring at least a first predetermined power amount in case the balance output signal indicates that the first number is equal to the second number; and
a second operating mode of the load unit requiring a second power amount smaller than the first power amount, or to shut down operation of the load unit, in case the balance output signal indicates that the first number is not equal to the second number.
9. A method for detecting a mode of power delivery by an external DC power sourcing equipment via four pairs of external electrical conductors corresponding to at least four pairs of power-input elements for connecting to the at least four pairs, the method comprising:
performing, by a balance measurement unit comprising two voltage dividers, each having a pair of inputs connected with a respective pair of power-input elements, and having respective center point taps, and a voltage sensor connected to the center point taps, and before power is drawn for operation of the DC-powered device, a balance measurement for determining whether or not a first number of pairs of external electrical conductors, from which a positive power-supply voltage is available, is equal to a second number of pairs of external electrical conductors, from which a negative power-supply voltage is available, wherein the balance measurement unit is configured to measure a center point voltage provided between the center point taps and a reference voltage and to provide the center point voltage as the balance output signal; and
providing a balance output signal indicative of a result of the balance measurement.
10. The method of claim 9 , further comprising:
performing, only in case the balance output signal indicates that the first number is equal to the second number, a power-limit measurement for determining a total amount of DC power available via the external electrical conductors; and
providing a power output signal indicative of a result of the power-limit measurement.
11. A method for operating a DC-powered device having a DC power input unit comprising at least four pairs of power-input elements, the method comprising:
performing a method according to claim 9 ;
determining and setting an operating mode of the DC-powered device in dependence on the balance output signal.
12. The method of claim 11 , further comprising determining and setting:
a first operating mode of the load unit requiring at least a first predetermined power amount in case the balance output signal indicates that the first number is equal to the second number; and
a second operating mode of the load unit requiring a second power amount smaller than the first power amount, or to shut down operation of the load unit, in case the balance output signal indicates that the first number is not equal to the second number.
13. A computer program comprising executable code for executing a method for operating a DC-powered device according to claim 11 when executed by a processor of a computer.