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US 4,789,842 AGranted
Composite transistor device with over-current protection
OwnerJiri Naxerainventor
Life of this patent
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Abstract
A composite transistor device having over-current protection is disclosed, and particularly a device for protecting Darlington configuration power transistor devices. The over-current protection circuit operates to clamp the base-emitter potential of the exciter transistor thus causing the power output transistor to maintain a power output below a predetermined threshold value. This allows the control of the power output intensity so as to avoid damage to the circuit, and with a minimum of power losses due to active voltage losses.
Claims11
A composite transistor device having over-current protection comprising:
- (a) a sensing resistor having a first resistor electrode and a second resistor electrode;
- (b) a power output transistor means having an emitter electrode, a base electrode and a collector electrode;
- (c) an auxiliary transistor being of opposite conductivity type to said power output transistor means and having an emitter electrode and a base electrode for detecting an over-current condition in said composite transistor device, and having a collector electrode for providing a signal means indicative of said over-current condition;
- (d) an exciter transistor being of opposite conductivity type to that of said power output transistor means and having an emitter electrode, a base electrode and a collector electrode,
- where said collector electrode of said power output transistor means, said first resistor electrode and said base electrode of said auxiliary transistor are interconnected, and
- where said second resistor electrode, said emitter electrode of said auxiliary transistor and said emitter electrode of said exciter transistor are interconnected, and
- where said base electrode of said power output transistor means and said collector electrode of said exciter transistor are interconnected, and
- where said base electrode of said exciter transistor and said collector electrode of said auxiliary transistor are interconnected so as to clamp the base-emitter potential of said exciter transistor and
- whereby said device provides:
- for a detecting means for detecting said over-current condition, said over-current condition being manifested when the collector current flow of said power output transistor means flowing through said sensing resistor exceeds a predetermined value, thus triggering said signal means indicative of said over-current condition;
- for a clamping means for clamping the base-emitter potential of said exciter transistor in response to said signal means;
- and
- for a current flow limiting means for limiting the collector current flow of said power output transistor means to a value less than said predetermined value.
10 more elements
A composite transistor device having over-current protection comprising:
- (a) a sensing resistor having a first resistor electrode and a second resistor electrode;
- (b) a power output transistor means having an emitter electrode, a base electrode and a collector electrode;
- (c) an exciter transistor being of same conductivity type to said power output transistor means and having an emitter electrode, a base electrode and a collector electrode;
- (d) an auxiliary transistor being of opposite conductivity type to that of said power output transistor means and having an emitter electrode, a base electrode and a collector electrode, said auxiliary transistor being connected so that when said emitter and base electrodes detect an over-current condition in the collector current flow of said power output transistor means, characterized in the current flowing through said sensing resistor exceeding a predetermined value, said collector electrode provides for a signal means indicative of said over-current condition;
- and
- (e) a clamping transistor means for clamping the base-emitter potential of said exciter transistor transistor in response to said signal means indicative of said over-current condition, said clamping transistor being of the same conductivity type to said power output transistor means.
3 more elements
Dependencies are inferred from the claim text.