# US 10,122,164 B2 · Protection device and protection method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,122,164 B2 - Document ID: US10122164B2 - Status: Granted - Kind: B2 - Application number: 14/787,009 - Filed: 2013-05-14 - Published: 2016-04-14 - Granted: 2018-11-06 - Earliest claimed: 2013-05-14 - Assignees: Mitsubishi Electric Corporation - Applicants: Mitsubishi Electric Corporation - Inventors: Takuya Mukai; Yoshiaki Koizumi - Web page: https://patentgrep.com/patent/US10122164B2 ## CPC - H02H 9/025: {Current limitation using field effect transistors} - F24F 11/30: for purposes related to the operation of the system, e.g. for safety or monitoring - F24F 11/62: characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values - F24F 11/63: Electronic processing - F24F 11/88: Electrical aspects, e.g. circuits - F24F 2221/32: preventing human errors during the installation, use or maintenance, e.g. goofy proof - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - F24F: AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING (removing dirt or fumes from areas where they are produced B08B15/00; vertical ducts for carrying away waste gases from buildings E04F17/02; tops for chimneys or ventilating shafts, terminals for flues F23L17/02) ## Abstract A current path of a first transistor is connected in series to a communication line. When the electric current through the current path of the first transistor becomes equal to or greater than a set electric current, a current-limiting controller limits the electric current through the current path by controlling the first transistor to increase the resistance of the current path. When the end-to-end voltage of the current path of the first transistor becomes equal to or greater than a set voltage, a load limiter switches the first transistor off. ## Claims ### Claim 1 A protection device for an air conditioning system, the air conditioning system including air conditioning units connected to each other by connection lines including a communication line, a power source line and a common line, the protection device comprising: a first transistor including a first current path connected in series with the communication line; and a current-limiting controller configured to limit an electric current flowing in the first current path by controlling the first transistor so that a resistance value of the first current path increases, when the electric current flowing in the first current path is equal to or greater than a set electric current; and a current interrupt controller configured to turn off the first transistor when an end-to-end voltage of the first current path is equal to or greater than a set voltage while the first transistor is operating in an active region, wherein the protection device is configured to prevent an excess electric current from flowing in the communication line. ### Claim 2 (depends on 1) The protection device according to claim 1, wherein the protection device is installed in a main air conditioning unit and one of secondary air conditioning units. ### Claim 3 (depends on 1) The protection device according to claim 1, wherein the current interrupt controller comprises a second transistor configured to cause a voltage impressed between first control terminals configured to control the resistance value to fall so that the first transistor is turned off, by turning on when a voltage corresponding to the end-to-end voltage is impressed and the end-to-end voltage becomes equal to or greater than the set voltage. ### Claim 4 (depends on 3) The protection device according to claim 3, wherein the second transistor includes a second current path having one end connected to one end of the first current path and having the other end connected to one of the first control terminals, the second transistor configured to cause the voltage impressed between the first control terminals to fall so that the first transistor is turned off by turning on when the voltage corresponding to the end-to-end voltage is impressed between second control terminals configured to control the second transistor, and the voltage generated between the one end and the other end of the first current path becomes equal to or greater than the set voltage. ### Claim 5 (depends on 4) The protection device according to claim 4, wherein the current-limiting controller comprises a third transistor configured to cause the voltage impressed between the first control terminals to fall so that the resistance value is increased, by turning on when a voltage corresponding to the electric current flowing in the first current path is impressed and the electric current flowing in the first current path becomes equal to or greater than the set electric current. ### Claim 6 (depends on 5) The protection device according to claim 5, wherein: the current-limiting controller comprises a resistor configured to impress the voltage corresponding to the electric current flowing in the first current path between third control terminals configured to control the third transistor; and the third transistor causes the voltage impressed between the first control terminals to fall and causes the resistance value to increase, by turning on when the electric current flowing in the first current path becomes equal to or greater than the set electric current. ### Claim 7 (depends on 6) The protection device according to claim 6, further comprising a first photocoupler configured to cause a first phototransistor to output a signal, by a signal electric current that flows when the second transistor turns on being conducted to a first photodiode. ### Claim 8 (depends on 7) The protection device according to claim 7, further comprising: a second photocoupler including a second photodiode through which an electric current flows in accordance with an outside signal from an outside, and a second phototransistor including a fourth current path that is turned on by light emitted from the second photodiode and is connected in series with the communication line; and a voltage limiter connected in parallel with the fourth current path and configured to limit the voltage impressed on the fourth current path. ### Claim 9 (depends on 8) The protection device according to claim 8, wherein the protection device is placed in a closed circuit formed when a power source is connected to the communication line. ### Claim 10 A protection method for a protection device for an air conditioning system, the air conditioning system including air conditioning units connected to each other by connection lines including a communication line, a power source line and a common line, the protection method comprising: limiting an electric current flowing in a current path of a first transistor, the current path being connected in series with the communication line, by controlling the first transistor so that a resistance value of the current path increases, when the electric current flowing in the current path is equal to or greater than a set electric current; and turning off the first transistor when an end-to-end voltage of the current path is equal to or greater than a set voltage while the first transistor is operating in an active region, wherein the protection method prevents an excess electric current from flowing in the communication line.