Cut-off tube controlled discharge delay circuit

8. Cut-off tube controlled discharge delay circuit

Compared with the discharge delay circuit and the charging delay circuit, the discharge delay circuit can obtain a longer delay, and the delay
accuracy is relatively high.
    The circuit is shown in the figure, which is a schematic diagram and a waveform diagram of input and output.
    Under normal circumstances, when there is no signal input, the transistor VTi is turned off, VT2 and VTa are turned on, and U is output. . is zero potential .
When U9r signal voltage makes VTi conductive, VT2 is cut off, VT3 is still conductive, U. . is zero potential. After a delay,
VT2 is turned on, VT3 is turned off, and U is output. . is a high potential. When the input signal disappears, VTi returns to cut-off, and VT2 and
VT3 are turned on.
    The Usr signal appears to U. . The time interval between becoming high potential is the delay time ￡, t can be calculated according to the following formula:
    t=O. 7(Rs+RP)C (s)
In the formula, the unit of R5 and RP is 0, and the unit of C is F .