Abstract: There is provided a power amplifier circuit with improved operation speed of the protection function against overcurrent or overvoltage. The power amplifier circuit includes an amplifier configured to amplify a radio frequency signal and output the radio frequency signal, a bias current supply circuit configured to supply a bias current to the amplifier, a detection circuit configured to detect whether the current or voltage of the amplifier is equal to or greater than a predetermined threshold; and a draw circuit configured to, when the detection circuit detects that the current or voltage is equal to or greater than the predetermined threshold, draw at least a part of the bias current supplied to the amplifier.

Abstract: A sintered friction material is formed by pressure sintering mixed powder at 800° C. or above, the mixed powder consisting of, in mass %, Cu and/or Cu alloy: 40.0 to 80.0%, Ni: 0% or more and less than 5.0%, Sn: 0 to 10.0%, Zn: 0 to 10.0%, VC: 0.5 to 5.0%, Fe and/or Fe alloy: 2.0 to 40.0%, lubricant: 5.0 to 30.0%, metal oxide and/or metal nitride: 1.5 to 30.0%, and the balance being impurity.

Abstract: A sintered friction material is formed by pressure sintering mixed powder at 800° C. or above, the mixed powder consisting of, in mass %, Cu and/or Cu alloy: 40.0 to 80.0%, Ni: 0% or more and less than 5.0%, Sn: 0 to 10.0%, Zn: 0 to 10.0%, VC: 0.5 to 5.0%, Fe and/or Fe alloy: 2.0 to 40.0%, lubricant: 5.0 to 30.0%, metal oxide and/or metal nitride: 1.5 to 30.0%, and the balance being impurity.

Abstract: A sintered friction material for use in a high-speed railway is manufactured using a Cu alloy powder produced using an atomizing method from a Cu alloy containing 0.1 to 2.0 mass % of Fe. This friction material has both sufficient high strength and high thermal conductivity.

Abstract: Provided is a sintered friction material exhibiting high braking power, and being excellent in stability of braking power at a high temperature. The sintered friction material of the present invention includes a chemical composition containing: by mass %, Fe of 7.5% or more, Cu of 50% or more, graphite of 5 to 15%, molybdenum disulfide of 0.3 to 7%, and silica of 0.5 to 10%, wherein Fe/Cu is 0.15 to 0.40.