| 摘要 |
A start-up and bias circuit provides a known, fixed bias point suitable for generating fixed bias currents for use in other circuits, which remains fixed regardless of variations in a start-up signal. A first transistor conducts a current in response to the start-up signal, which is mirrored to a second transistor driven from a node that increases linearly with the conducted current. When the conducted current reaches a predetermined threshold, the second transistor sinks all of the mirrored current and the operating point of the first transistor stabilizes. A third transistor is connected to oppose increases in the start-up signal beyond that required to maintain the predetermined threshold current. When stabilized, the virtually constant current in the first transistor provides a fixed bias point; a number of other transistors can be connected to the bias point to mirror the constant current and thereby produce individual fixed bias currents for use in other circuits. A thermal shutdown circuit uses the difference in the base-emitter voltages of a pair of differently-sized transistors to indicate an excessive temperature condition, which can be used, for example, to reduce the bias current supplied to a voltage regulator to near zero.
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