Darlington circuit having means for detecting a line interruption in its load circuit
AssigneeRobert Bosch GmbH
InventorHartmut Michel
Life of this patent
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Abstract
A resistor (16) is connected in parallel with the base-emitter section of the power transistor (12) of a Darlington circuit (10-12) to detect a line interruption in its load circuit. Furthermore, circuit components (17) are provided, which are able to be controlled through the voltage dropping across the resistor (16) and which are able to be transformed into a second circuit state characterizing a line interruption when this voltage drops below a specifiable value. In this manner, through the application of a few simple and inexpensive components, a line interruption can be reliably detected in the load circuit without the use of a measuring resistor.
Claims11
A circuit arrangement comprising:
- first circuit means including a prior transistor and a power transistor, with a base of the power transistor being connected to an emitter of the prior transistor, and with a collector of the power transistor being connected to a collector of the prior transistor for connection to a load circuit and with a base of the prior transistor being coupled to a control input;
- a resistor with a first terminal being connected to the base of the power transistor and a second terminal being connected to an emitter of the power transistor;
- and
- a load circuit interruption detector with a first input connected to the base of the power transistor and a second input connected to the control input, with an output voltage of the load circuit interruption detector switching from a first value to a second value when a voltage drop across the resistor decreases below a predetermined threshold voltage and while an input voltage is applied to the control input which would otherwise cause the power transistor to be in an on state if there were no interruption in the load circuit, thereby indicating a line interruption in the load circuit.
A method of detecting a line interruption in a load circuit connected to a collector of a power transistor connected with a prior transistor in a circuit arrangement, comprising the steps of:
- (a) determining whether a voltage across a resistor connected between a base and an emitter of the power transistor falls below a predetermined threshold voltage;
- (b) determining whether an input signal is being applied which would cause the power transistor to be in an on state if there were no interruption in the load circuit;
- and
- (c) switching an output voltage of a load circuit interruption detector having a first input coupled to the base of the power transistor, and a second input connected to the input signal from a first value to a second value when the determinations at steps a) and b) are both true, with the second value being indicative of a line interruption.
Dependencies are inferred from the claim text.