Protective means for transistorized load circuit

Claim 2

The invention as defined in claim 1 including reference voltage means connected with the input of the voltage responsive means whereby said predetermined value of voltage is established.

Claim 3

The invention as defined in claim 1 including bias means for maintaining the voltage across the load device above said predetermined value when said intermittent control signal causes the switching device to turn off in the absence of a short circuit across the load device.

Claim 4

The invention as defined in claim 1 wherein said voltage responsive means is operatively connected with said oscillator and is adapted to change from said second conductive state to said first conductive state upon removal of a short circuit across said load device and thereby restore switching control to said intermittent control signal.

Claim 5

A flasher circuit for use with an automotive vehicle and adapted to intermittently energize selected lamps of the vehicle from a battery and comprising a free-running oscillator for producing an intermittent control signal, a switching device adapted to be switched between on and off conditions in response to said intermittent control signal to connect and disconnect the load device and said battery, amplifying means having an input operatively connected with the output of said oscillator and having an output connected with said switching device, voltage responsive means having an input adapted to be connected with the load device and an output connected to the input of said amplifying means, said voltage responsive means being effective to disable said amplifying means when the voltage across the input of the voltage responsive means is below a predetermined value, bias means connected with the input of said amplifying means to maintain said amplifying means disabled until the voltage across the load device exceeds a predetermined value, the output of said amplifying means being connected with said switching device to switch it off in the absence of a control signal being applied through said amplifying means to said switching device whereby a short circuit across said load device will reduce the voltage at the input of the voltage responsive means to a value below said predetermined value and will disable said amplifying means to thereby prevent said intermittent control signal from turning on said switching device for the duration of said short circuit.

Claim 6

The invention as defined in claim 6 wherein said switching device is a power transistor adapted to have its output connected with said lamps and wherein said amplifying means comprises a driver transistor having its output connected with the input of the power transistor, said voltage responsive means including a semiconductor switching device having an input and a common electrode connected with a reference voltage device and adapted to be connected in circuit with said load device, said semiconductor switching device having an output electrode and said common electrode connected in circuit with the input of said driver transistor.

Claim 7

The invention as defined in claim 7 wherein said semiconductor switching device is operatively connected with the output of said free-running oscillator and is adapted to change from a conductive state to a nonconductive state in the absence of said control signal whereby the voltage responsive means is operative to restore switching control to said oscillator upon removal of said short circuit.

Claim 8

The invention as defined in claim 6 wherein said amplifying means comprises a driver transistor, and said switching device comprises a power transistor and said voltage responsive means comprises a controlled rectifier, a zener diode connected in the input of said driver transistor, said silicon controlled rectifier having its anode and cathode connected between said zener diode and said load device and having its gate electrode connected to a reference voltage device whereby said controlled rectifier becomes conductive when the voltage across the load decreases below said predetermined value and said zener diode blocks input current to said first transistor when the voltage across the load device is below said predetermined value.

Claim 9

The invention as defined in claim 7 wherein said semiconductor switching device is a controlled rectifier and said reference voltage device is a voltage reference transistor having an output adapted to be connected across the battery and an input connected with the output of said driver transistor, said controlled rectifier having its output electrodes connected between the input of said driver transistor and said load device, said controlled rectifier having its input electrodes connected between the input of said driver transistor and the output of said voltage reference transistor.

Claim 10

The invention as defined in claim 10 wherein a zener diode is connected in the input of said driver transistor.

Claim 11

The invention as defined in claim 10 including a switching transistor connected between the output of said oscillator and the input of said driver transistor whereby said controlled rectifier is switched off during alternate half-cycles of said oscillator and the load device is periodically tested for the removal of the short circuit.