Patent ID: 7518429
Filing Date: 2009-04-14
Classification: H03H,H03K

Abstract:
1. A delay circuit, comprising: an RC circuit comprising a resistor having one end configured for receiving an input signal and an opposite end, and a capacitor connected to the opposite end of the resistor a discharging circuit connected to the RC circuit for controllable discharging of the capacitor, the discharging circuit comprising a controllable current path connected between the capacitor and ground, and a control terminal connected to the one end of the resistor configured for sensing a status of the RC circuit to control conduction of the path, the discharging circuit comprises a PNP type transistor and an NPN type transistor, a base of the PNP type transistor acts as the control terminal, an emitter of the PNP transistor is connected to a high level voltage signal, a collector of the PNP type transitor is connected to ground via a resistor, a base of NPN type transistor is connected to the collector of the PNP type transistor, a collector of the NPN type transistor is connected to the capacitor, and an emitter of the NPN type transistor is connected to ground; wherein when the control terminal senses the RC circuit starts charging, the control terminal closes the path such that the capacitor charges gradually, and when the control terminal senses the RC circuit starts discharging, the control terminal opens the path to quickly discharge the capacitor.