Automatic exposure control for a camera shutter

摘要

The specification discloses an automatic shutter timing control for a camera. A voltage supply is applied to a capacitor (38). An electronic switch such as a PMOS gate (44) has conductive and non-conductive states and is connected across the capacitor (38). A pair of transistors (32) and (40) are interconnected in a current mirror configuration and are connected between the voltage supply and the capacitor (38) and are operable in conjunction with a charging resistor (30) such that the capacitor (38) may be charged to a predetermined voltage when the PMOS device (44) is in a non-conductive state. A transistor (54) is operable to receive an electrical control signal in order to sink current from the charging resistor (30) and to prevent current flow through the PMOS device (44). A comparator (42) is responsive to a predetermined voltage on the capacitor (38) to control the camera shutter.