Electrical – How to turn off 555 Timer for a period of time after Vout signal passes through

You can't use the main timing resistor and capacitor to generate your trigger signal. As you discovered, this is exactly equivalent to the astable configuration.

Instead, you need to provide a separate resistor (to Vcc) and capacitor (to ground) for the Trigger pin. The time constant for this pair should be short relative to the main timing period, but long relative to the risetime of the power supply.

These components will hold the trigger low while the chip powers up, but then allow it to go high a short time later. Once the timer has timed out, the main timing capacitor will be discharged, but the trigger capacitor will not.

To use a 7555 here you have to deal with two problems, first you have a high going control signal and second how do you retrigger the 555.

The first is fairly easy you use a simple transistor inverter to invert the input signal.

The second takes a little more understanding of how the 555 is working. It charges up the timing capacitor until it reaches a threshold voltage and then turns off. You can retrigger it by discharging the capacitor.

Look at this circuit.

Q1 and R1 invert the incoming signal to make trigger active low Q2 discharges the capacitor while the input is high giving you the retrigger function. Note with this circuit your timing period is from the input signal going low.