Abstract A miniature calculator is provided with a keyboard having a small opening which has a recessed operating switch which may be pressed by the user. The operating switch is recessed so that accidental operation of the switch is difficult. When the calculator is turned on and the button is pressed, the calculator will turn off. When the calculator is off, and the button is depressed for less than 2 seconds, the calculator will turn on. If the calculator is off and the button is depressed for longer than 2 seconds, the calculator will switch off after the two second delay, since this is an apparent accidental depression. A logic circuit controls the connection of a regulated power supply to the calculator circuitry in accordance with the condition of the push button in the keyboard. The regulated power supply is a current supply which contains circuitry which eliminates the ''''low end'''' problem wherein regulated output voltage is provided even after substantial decrease of the battery voltage. The calculator also has a display time-out circuit such that the numerals of the display flash on and off at a relatively short duty cycle of, for example, 2 percent, after the display has been on for a given time in order to conserve battery power. A low battery voltage circuit is also provided to cause the flashing of a dot in the display.
A regulated d-c power supply circuit for a portable battery powered electrical device; said regulated d-c power supply circuit including input terminals connected to a battery power source, a series pass first transistor, output terminals connected in series with said first transistor and said battery power source and having a regulated output voltage appearing thereat; a second transistor connected to inject base current into said first transistor for controlling the conductivity of said first transistor from an off condition to a full saturation condition; a third transistor coupled to said output terminals and to said second transistor and being operable in response to the voltage of said output terminals to control the conductivity of said second transistor such that the base current injected into said first transistor tends to produce a voltage drop across said first transistor as needed to produce a given regulated voltage output at said output terminals; an on-off control circuit for turning said second transistor on and off thereby to turn said first transistor off in the off condition of said control circuit, and for permitting said second transistor to regulate the operation of said first transistor in the on condition of said control circuit; said on-off control circuit comprising a reset flip-flop circuit means connected between said battery and said second transistor, and means for operating said flip-flop circuit means between a set condition and a reset condition which respectively permits and prevents connection between said battery and said electrical device; said means for operating said flip-flop circuit means including a mechanical switch whereby closing of said switch causes said flip-flop circuit means to reset from a set condition and causes said flipflop circuit means to set from a reset condition.
Claim 2
Dependent Claim
286 words
A regulated d-c power supply circuit for a portable battery powered electrical device; said regulated d-c power supply circuit including input terminals connected to a battery power source, a series pass first transistor, output terminals connected in series with said first transistor and said battery power source and having a regulated output voltage appearing thereat; a second transistor connected to inject base current into said first transistor for controlling the conductivity of said first transistor from an off condition to a full saturation condition; a third transistor coupled to said output terminals and to said second transistor and being operable in response to the voltage of said output terminals to control the conductivity of said second transistor such that the base current injected into said first transistor tends to produce a voltage drop across said first transistor as needed to produce a given regulated voltage output at said output terminals; an on-off control circuit for turning said second transistor on and off thereby to turn said first transistor off in the off condition of said control circuit, and for permitting said second transistor to regulate the operation of said first transistor in the on condition of said control circuit; said on-off control circuit comprising a reset flip-flop circuit means connected between said battery and said second transistor, and means for operating said flip-flop circuit means between a set condition and a reset condition which respectively permits and prevents connection between said battery and said electrical device; said means for operating said flip-flop circuit means including a mechanical switch whereby closing of said switch causes said flip-flop circuit means to reset from a set condition and causes said flipflop circuit means to set from a reset condition.
Claim 3
Dependent Claim
104 words
The power supply of claim 1, wherein said electrical device is contained within an enclosing housing; said housing having an aperture therein; said on-off control circuit including a push button type switch means, whereby application of pressure to said push button type switch means switches said electrical device between first and second operational conditions; said push button type switch means being recessed within said aperture and accessible through said aperture; said aperture having a diameter sufficiently large to enable operation of said switch means by a human finger; said switch means being recessed in said aperture to prevent inadvertent operation of said switch means.