In a circuit of the type in which a command signal actuates a semiconductor switch which, in turn, actuates a load device and in which a clock signal is available, a protection circuit for protecting the semiconductor switch located in series with the load from excessive current in the event the load device is short circuited. The protection circuit includes a sensing circuit for sensing the voltage level at a point intermediate the semiconductor switch and the load. The protection circuit interfaces between the command signal and the clock signal in such a manner that the semiconductor switch is repeatedly momentarily energized if the load is shorted and a command signal is present.
Driver circuit for short-circuit-proof readout with a plurality of protection-wired inputs and outputs, including three comparators being connected to the inputs and being referred to a reference voltage, a first AND gate being switched into conduction if a positive voltage is present at the first comparator, a first switch being opened when the first AND gate is conducting and being connected to negative potential when closed, three current sources being connected to the outputs and to the first switch, a Darlington stage being connected to the outputs and to the current sources, an evaluation unit being connected to the outputs and to the current sources, an OR gate being influenced by the evaluation unit, a second switch being operated by the OR gate, an external capacitor input connected to the second switch for charging through a fourth current source and discharging through a current sink, three Schmitt triggers being different thresholds and being charged through the capacitor terminal, a second AND gate connected to the OR gate for controlling charging and discharging, and a second transistor stage connected to the outputs and to the Schmitt triggers.
An electronic current overload protection device in which an applied voltage is divided into the voltage across the load and the current-proportional voltage drop at an MOS transistor of a circuit that includes the load and the MOS transistor whose resistance is exactly linearly proportional to the current; this voltage drop is applied by way of a delay circuit to a threshold switch that controls the gate input of the MOS transistor by way of a driver stage; the threshold of the threshold circuit is adjustable corresponding to the current to be protected against.
A first electronic device, such as a computer, is connected to a second electronic device, such as a printer, over a communication bus. The second electronic device has device specific integrated circuitry for performing the functions of the device, and also has pad driver circuitry. The pad driver circuitry is connected between the communication bus and the device specific integrated circuitry. The first electronic device is powered by a first voltage source, such as AC power through an on/off switch. The second electronic device is powered by a second voltage source, such as AC power through a different on/off switch. In addition to being powered by the second voltage source, the pad driver circuitry is also powered by a third voltage source, isolated from the second voltage source. When the pad driver circuitry in the second device detects that the first device is powered-on and the second device is powered-off, it assures that the device specific circuitry in the second device will not become inadvertently powered-on by the first device through the communications bus. Pad driver circuitry also assures that power from the first device through a data line on the communications bus is not inadvertently fed back to the first device through a different data line on the communications bus. Pad driver circuitry also assures that current from the first device is not sunk (i.e. finds a path to ground) through the pad driver circuitry.
Motor control circuits having solid-state switching elements are commonly used on industrial vehicles such as lift trucks. A short circuit condition in the motor circuit can cause catastrophic failure of the semiconductor switching element. The instant invention detects such a short circuit condition and modifies the motor control signals supplied by a chopper circuit to a switching element. The apparatus includes a trigger circuit for receiving the motor control signals and sensing a voltage across the motor produced in response to electrical power delivered from a power supply.
An operation halting circuit comprises a circuit for controlling a system which executes a specified operation and a circuit for shutting off every input to the control circuit so as to prevent the supply voltage from being applied to the control circuit when the supply voltage drops below a specified threshold value.
