NE555: NE555 SHC Review

Bin Long

Prodigy 160 points

Part Number: NE555
Other Parts Discussed in Thread: SN74LV123A

Dear Sir

I want to design a signal delay circuit base on NE555. The SCH as below:

Target: The CARIN_ON signal must delay ACC_ON signal 10second .

Test result: CARIN_ON signal had not any delay.

Could you please help to review below SCH and give me some proposal to improve the circuit and make sure the circuit must be achieve the target? Thank you!

PS. below test waveform for you reference(Yellow:ACC_ON Blue: CARIN_ON)

over 8 years ago

0 Ron Michallick over 8 years ago

TI__Guru**** 165376 points

Bin,

To delay the signal rising a falling edges by 10 seconds, I suggest a completely different solution.

Here is the block diagram,

Here is schematic for unbalanced delay. This will start the SN74LV123A timer on both edges of ACC_ON

A power start up state circuit should be added too.

This solution is untested.

0 Dave chen1 over 8 years ago

Prodigy 10 points

why this circuit can't use for 10S delay？ why?

0 Bin Long over 8 years ago in reply to Ron Michallick

Prodigy 160 points

Dear Ronald
Could you please give us some proposal to improve the SHC base on NE555? Because of the schedule is very urgent, and we have no time to prepare samples for test.
Thank you very much!

0 Ron Michallick over 8 years ago in reply to Bin Long

TI__Guru**** 165376 points

Bin,

The timer is working. A low input starts the timer that outputs high for the duration of the timer period (can be 10 seconds with right values).

So the falling edge of the NE555 needs to turn on a latch. A 2nd NE555 can latch the 1st NE555 signal by using its trigger input. The output of the second NE555 will be correct CARIN_ON signal.

Invert ACC_ON signal and send that to 3rd NE555 trigger which is a 10 second timer just like 1st NE555. The output need to be inverted and sent to threshold of 2nd NE555

The 3 NE555 plus two inverters can do it. Use reset to power up in off state.