[0001] The present disclosure relates generally to ("lass 2 electrical circuits and, more particularly, to protecting such circuits with fewer protection devices than heretofore.

[0002] The National Electrical Code (NEC) is a North American standard that describes the installation of electric conductors and equipment within or on buildings. The NEC is the source of the Class 2 electric circuit definition, which limits the maximum voltage and current in the electric circuit, Class 2 defines the portion of the wiring system between a power supply, e.g., typically rated at 24VDC and 100W maximum, and one or more loads. Due to its power, voltage, and current limitations, the Class 2 circuit specifies, among other things, acceptable safety protection against electric shock,

[0003] The American National Standard Institute (ANSI) Underwriters Laboratories

(UL) standards for electrical circuit safety include the UL-1310 Standard for Class 2 circuits. The UL-1310 Standard requires, among other things, that for a circuit to have a Class 2 rating, the circuit must be able to limit power, voltage, and current values despite a single electrical component failure in the circuit. To limit such electrical values, it is known to provide the circuit with various combinations of such protection devices as current sensors, voltage sensors, thermal cut-off protectors, switches, relays, comparators, microcontrollers, eFuses, and so on.

[0004] To meet the UL-1310 Standard for safety, it is known to provide a first protection device (PD) and a second redundant PD between a power source and each load. Thus, as shown in FIG. 1 A, it is known to insert two PDs in a primary line to the load, and, as shown in FIG, IB, it is also known to insert the first P D in a primary line, and the second PD in a secondary line, to the load. The PDs can be located on any combination of primary and se

conventional to provide two PDs for each load.

[0005] As advantageous as these known protection devices are, it would be desirable to reduce the cost and complexity of such Class 2 circuits, and to decrease the number of protection devices required, while still maintaining the Class 2 rating.

[0006] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.

[0007] FIG. 1A is an electrical schematic depicting one version of how protection devices may be installed in a Class 2 circuit, in accordance with the prior art,

[0008] FIG. 1 B is an electrical schematic depicting another version of how protection devices may be installed in a Class 2 circuit, in accordance with the prior art,

[0009] FIG, 2 is an electrical schematic depicting how protection devices may be installed in a Class 2 circuit, in accordance with the present disclosure.

[0010] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

[0011] The circuit components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the b

herein,

[0012] In accordance with one feature of this invention, an electrical circuit is connected between a power source and a plurality of loads. The circuit includes a plurality of load protection devices thai are connected in parallel in individual branches of a sub-circuit. Each one of the load protection devices is connected to each load in an individual branch, A single power protection device is connected in series between the power source and the sub-circuit. Each one of the load protection devices in a respective branch and the single power protection device enable the circuit to have a Class 2 rating,

[0013] Turning now to FIG. 2 of the drawings, an electrical circuit is connected between a power source that supplies electrical power, and a plurality of loads that consume the electrical power. The power source is typically rated at 24V DC and 100W maximum. Although four loads ha ve been illustrated, any number of loads is envisioned by this disclosure. The loads are preferably DC loads, and in the illustrated case, each can handle 100W/4 = 25 W. Each load is located in a branch of a multi-branch sub-circuit,

[0014] As described above in connection with FIGs. 1 A, 1B, in order for the circuit to have a Class 2 rating, two protection devices need to be connected to each load in a respective branch of the multi-branch, sub-circuit. In other words, the number of PDs is equal to two times the number of Class 2 circuit branches and loads being protected. Thus, according to the prior art, eight (2 protection devices x 4 loads) protection devices would be needed. This invention is directed to reducing this number of protection devices, for example, to the illustrated five protection devices, while still maintaining the Class 2 rating. [0015] As shown in FIG. 2, the circuit includes a plurality of

(LPDs) that are connected in parallel in the individual branches of the multi -branch, sub-circuit. Each one of the load protection devices LPDs is connected to each load in an individual branch. A single power protection device (PPD) is connected in series between the power source and the sub-circuit. The circuit maintains its Class 2 rating, because each load is protected by the single PPD and the one LPD in each branch. The single PPD is shared by all of the loads and the branches. Thus, the number of protection devices is equal to one (i.e., the single PPD) plus the number of individual Class 2 branches and loads (as illustrated, four) being protected. The aggregate power consumed by all the loads is less than the maximum output power of the power source. Thus, if the po wer source is 100W maximum, then the aggregate power consumed by all the loads is less than 100W, per the UL-131G Standard.

[0016] If the current, voltage, or power in the individual branches is independently measured, and if the shutdown action of the protection devices is independently performed in the individual branches, then the above-described redundant protection can be used for multiple sets of branches and sub-circuits. Also, if the current, voltage, or power in the individual branches is independently measured, and if the shutdown action of the protection devices is independently performed in the individual branches, then a single protection device can monitor multiple branched and sub-circuits. Put another way, a single device can toggle between a plurality of branches and sub-circuits, or can toggle between multiple ports.