Abstract: It is described a thermoplastic composition comprising. (A) 10 to 99% by weight of a propylene polymer optionally containing from 0.1 to 5% by moles of units deriving from an olefin of formula CH2═CHR, R being hydrogen, a C2-C20-alkyl or a C6-C12-aryl group, having the following characteristics: 50<isotactic triads (mm)<85; melting point (Tm) from 60° C. to 120° C., and (B) 1 to 90% by weight of a propylene polymer having an essentially isotactic structure, optionally containing from 0.1 to 5% by moles of units deriving from an olefin of formula CH2═CHR, R being hydrogen, a C2-C20-alkyl or a C6-C12-aryl group, which has a melting point (Tm) higher than 153° C. It is also described a process for the preparation of said thermoplastic composition.

Abstract: By driving the gate of a voltage-controlled semiconductor switch, positioned as the upper device in each leg of a DC to AC converter, from an extremely high impedance, the need for floating gate drive power sources is eliminated. The invention takes advantage of the inherent gate capacitance of the switch as an energy storage device.

Abstract: A low loss snubber provides stress relief for a first controllable semiconductor switch. The low loss snubber comprises a capacitor in series with a diode. This series combination is connected across the first switch, with the diode poled to conduct current to charge the capacitor when the first switch turns off. The low loss snubber further comprises an energy retrieval converter for removing energy from the capacitor when the first switch turns on. The energy retrieval converter has a second controllable semiconductor switch which is repeatedly turned on and off responsive to the first switch remaining in the closed position. An inductor means is in series with the second switch and the capacitor is provided for transferring the energy stored in the inductor means to an external load when the second switch is open.

Abstract: A pulse shaping circuit, for use with two-wire telephone station sets, such as normally associated with electronic private automatic branch exchange systems. The function of the pulse circuit is to regenerate hook-switch and hold-button control signal pulses for transmission to the common switching equipment as finite loop current interruptions of predetermined pulse width. The circuit overcomes false signalling and signal recognition problems caused by loop-current transient interruptions, and by imprecise manual operation of the station hook-switch and hold-button by station users.

Abstract: An energy limiting foldback circuit for use with power supply having a power control device in its output. The energy limiting foldback circuit contains a voltage sensing device for sensing the potential drop between the input and the output of the power control device. The foldback circuit also includes a current sensing device for sensing the current through the power control device. A conduction control circuit is included which is responsive to the outputs of the voltage sensing device and the current sensing device. The conduction control circuit acts to control the operating conduction through the power control device. The energy limiting circuit can also include a pulsing circuit operative in the event of output fault to periodically pulse the power control device into a momentary conduction state.