Delay turn ON circuit using 555

Question

I want to set a delay of around 5s between power supply turning ON and my circuit getting power.

Here is the circuit I have come up with:

I am using a 555 timer to set the startup delay and N-channel mosfet to supply power to the load. Most of the through hole mosfets have Rds minimum at around 10 V. Luckily I had 12V supply readily available so I am using 12 V to switch the 5V line as shown above. P4 is input and P3 is load.

Is my circuit correct?

Besides initial turn ON delay, I want the circuit to reset when power is disconnected (in half a min or so. if it happens within 1-2 seconds, it will be even better). To achieve this, I have put R7 (100K) discharge resistor on the capacitor which will discharge it and get the circuit in working state again. Is there a better way to do this?

You want it to wait five seconds, turn on, then in 1-2 seconds turn off again? If so, look up using the 555 in monostable one-shot mode. As in this question. — Samuel, Jan 31 '18 at 06:13
No, I want wait 5 seconds then turn ON and keep it turned ON until power is disconnected. — Whiskeyjack, Jan 31 '18 at 06:14
Ah, so the reset just means that it's ready to use a few seconds after you disconnect the power? — Samuel, Jan 31 '18 at 06:16
Yes (random text to reach min word count for posting this comment) — Whiskeyjack, Jan 31 '18 at 06:17

score 2 · Accepted Answer · answered Jan 31 '18 at 06:39

2

The circuit looks good.

If you want faster reset of the circuit move R7 to between 12V and GND and reduce its resistance... when the 12V is turned off C3 will discharge through D1 and the new R7

answered Jan 31 '18 at 06:39

Jasen Слава Україні

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Will it not affect the charging process? I am sorry but I am not able to visualize. – Whiskeyjack Jan 31 '18 at 06:49
the new location of R7 is connected to +12V and Gnd, it only affects the capacitor when the 12V is turned off. when the 12V is on it justs sits there making heat. – Jasen Слава Україні Jan 31 '18 at 06:51

Delay turn ON circuit using 555

1 Answers1