Power transistor protection circuit

Claim 2

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor said protective means comprising switch means operatively connected to said power transistor and effective to bypass said control signal from said power transistor when actuated, means for comparing said sum of said first and second signals with a constant voltage reference, the latter comprising means for determining said predetermined value, said constant voltage reference comprising a Zener diode in operative connection wIth said protective means.

Claim 3

The protection circuit of claim 1, in which said protective means comprises a semiconductor device effective to operate in the conducting state when said signals sum exceeds said predetermined value.

Claim 4

The protection circuit of claim 1, in which said protective means comprises a transistor having said Zener diode operatively connected in the base circuit thereof.

Claim 5

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, said protective means comprising switch means operatively connected to said power transistor and effective to bypass said control signal from said power transistor when actuated, and means connected in circuit with said protective means and effective to delay the response of said protective means to said signal''s sum when the latter exceeds said predominant value, and in which said protective means comprises a transistor having a base, emitter and collector terminal, said delaying means comprising a capacitor connected between said collector and said base terminal.

Claim 6

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, said protective means comprising switch means operatively connected to said power transistor and effective to bypass said control signal from said power transistor when actuated, and means connected in circuit with said protective means and effective to delay the response of said protective means to said signal''s sum when the latter exceeds said predominant value, and in which said protective means comprises a transistor having a base, emitter and collector terminal, said delaying means comprising a capacitor connected between said collector and said base terminal.

Claim 7

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, said first signal being a first voltage proportional to the current in said power transistor, and said second signal being a second voltage proportional to the voltage across said power transistor, means for comparing said sum of said first and second signals with a constant voltage reference, the latter comprising means for determining said predetermined value, said constant voltage reference comprising a Zener diode in operative connection with said protective means.

Claim 8

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, said first signal being a first voltage proportional to the current in said power transistor, and said second signal being a second voltage proportional to the voltage across said power transistor, means for comparing said sum of said first and second signals with a constant voltage reference, the latter comprising means for determining said predetermined value, said constant voltage reference comprising a Zener diode in operative connection with said protective means.

Claim 9

The protection circuit of claim 5, in which said protective means comprises a semiconductor device effective to operate in the conducting state when said signals sum exceeds said predetermined value.

Claim 10

The protection circuit of claim 5, in which said protective means comprises a transistor having said Zener diode operatively connected in the base circuit thereof.

Claim 11

The protection circuit of claim 5, comprising means connected in circuit with said protective means and effective to delay the response of said protective means to said signals sum when the latter exceeds said predetermined value.

Claim 12

The protection circuit of claim 8, in which said protective means comprises a transistor having a base, emitter and collector terminal, said delaying means comprisiNg a capacitor connected between said collector and said base terminal.

Claim 13

The protection circuit of claim 5, in which said voltage-sensing means further comprises voltage-limiting means effective to derive said second signal at said voltage-sensing means only when the voltage input across said power transistor exceeds a second predetermined level, said second predetermined level being established by said voltage-limiting means.

Claim 14

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, means for comparing said sum of said first and second signals with a constant voltage reference, the latter comprising means for determining said predetermined value, said constant voltage reference comprising a Zener diode in operative connection with said protective means, said protective means comprising a transistor having said Zener diode connected in the base circuit thereof.

Claim 15

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, means for comparing said sum of said first and second signals with a constant voltage reference, the latter comprising means for determining said predetermined value, said constant voltage reference comprising a Zener diode in operative connection with said protective means, said protective means comprising a transistor having said Zener diode connected in the base circuit thereof.

Claim 16

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, comprising means connected in circuit with said protective means, and effective to delay the response of said protective means to said signal''s sum when the latter exceeds said predominant value, in which said protective means comprises a transistor having a base, emitter and collector terminal, said delaying means comprising a capacitor connected between said collector and said base terminal.

Claim 17

In a power supply control circuit comprising a power transistor receiving a control signal corresponding to a comparison of the power supply output and a reference, thereby to vary the conductivity of said power transistor, and hence the level of the output, in response to said control signal, the improvement which comprises: a protection circuit for said power transistor comprising means for sensing the current in said power transistor and for deriving a first signal representative thereof, means for sensing the voltage applied across said power transistor and for deriving a second signal representative thereof, and protective means responsive to the sum of said first and second signals, operatively connected to the input of said power transistor, and effective when said sum exceeds a predetermined value to modify said control signal to decrease the conductivity of said power transistor, comprising means connected in circuit with said protective means, and effective to delay the response of said protective means to said signal''s sum when the latter exceeds said predominant value, in which said protective means comprises a transistor having a base, emitter and collector terminal, said delaying means comprising a capacitor connected between said collector and said base terminal.