A signal amplifier circuit arrangement includes an input amplifying circuit having a current mirror load circuit and an output transistor having its base connected to the output of the input amplifying circuit, its collector connected to the output terminal of the signal amplifying circuit and its emitter connected to a power supply terminal. In the signal amplifier circuit arrangement a current detection resistor is connected between the emitter of the output transistor and the power supply terminal and a diode is connected between the emitter or collector of the output transistor and the collector of a diode-connected transistor of the current mirror circuit. When a large current flows through the output transistor due to the short-circuiting of the output terminal, the diode connected in series with the emitter-base path of a transistor in the current mirror circuit is rendered conductive by a voltage drop developed across the current detection resistor, thus providing a current negative feedback to the base of the output transistor through the current mirror circuit for restricting the collector current of the output transistor.

The amplifier comprises a power suppl, a current sensing element for sensing a current in the current path of the power supply, a detecting circuit responsive to the current sensing element, and voltage reducing means for reducing the signal amplitude of at least one of the audio signals in response to the detection circuit. The detecting circuit comprises in a preferred embodiment a threshold circuit, and when the current in the current path of the power supply is above a predefined threshold, the detection circuit together with the voltage reducing means reduce at least the signal amplitude of one of the audio channels. The current sensing element is for example a current sensing resistor and the detecting circuit is a voltage detection circuit in parallel to this resistor. The voltage reducing means comprise advantageously two diodes for each channel, via which a positive and a negative voltage limit is applied to the signal path of the audio signals.

A solid state current sensing circuit which is useful in a power supply has bipolar as well as CMOS transistors. The bipolar transistors serve as output transistors and have lateral collectors as well as substrate collectors. The lateral collectors of the bipolar transistors are used to sense a portion of the current carried by the substrate collectors. The lateral collectors are connected to a current mirror which provides an output indication of when the output current exceeds a predetermined amount. The entire circuit can be integrated on a single chip.

A circuit to limit the maximum current passed from a power transistor (T'p) to a load (ZL) which is connected to an output terminal of the transistor. The circuit includes an error amplifier (1'), a driver circuit (P') for the transistor (T'p), and a current detector for detecting the current (IL) flowing through the load (ZL). The current detector is provided with at least first and second terminals, includes a circuit block (2) having an input terminal connected to the control terminal of (T'p) and an output terminal connected to the current generator internal to the amplifier (1'), one input (B') of the amplifier (1') being connected to the first terminal of (Rs) and the other input (A') connected to the second terminal of (Rs). The introduction of the circuit block lowers the open-loop system gain making it stable and producing a smooth reduction of any rise in the load current (IL).

An I.sup.2 L programmable read only memory (PROM) row driver circuit sinks current from a row of memory elements when selectively activated. The circuit operates in the read mode at very low power levels and down to 1.0 volt. The circuit has two current sinking capabilities, a low current capability for the read mode and a high current capability for the program mode. Switching between modes is accomplished merely by changing the voltage on a power supply terminal; 1-3 volts for the read mode and 9-12 volts for program.