Alternative long time 555 monostable.

Thread Starter

bertus

Joined Apr 5, 2008
20,869
Hello,

I got an article in Funk Amateur , a german magazine about a long time 555 monostable.
It uses the discharge transistor to charge the capacitor and a parallel resistor on the capacitor to perform the timing.
In this way you can even make long times upto 0.5 hours:

atlernative 555 monostable.jpg

Sorry for the german text, but the schematic will be clear.

Bertus
 

Dodgydave

Joined Jun 22, 2012
9,637
Yes it's the reverse method, where C1 is kept charged and when triggered R4 discharges it until it it reaches 2/3 supply, I've used this a few times you need good quality caps..
 

Thread Starter

bertus

Joined Apr 5, 2008
20,869
Hello,

For long timings, the leakage current can be to high.
If you use a large resistor, the current may not overcome the leakage current.

Bertus
 

crutschow

Joined Mar 14, 2008
25,632
I like the CD4060 with the 14 stage ripple counter
Yes, that's my preference also.
Besides using smaller resistors and capacitors, another advantage is that you can calibrate the time (if needed) by adjusting the period at Q4 which is a much shorter period than having to wait for the full timeout.
 
Timer blox LTC6995 from Analog Devices, Tiny eval board configurations interesting funktionsicherer.
Sort of a breakout board, after all the years of 555. compares to the timer blox.
The demo board has different configurations. (Version A) shows 1 kHz to 10 kHz VCO using 1MΩ optional pot
https://www.analog.com/media/en/technical-documentation/eval-board-schematic/DC1562B-SCH.PDF

Timer blox evaluation board uses buffers, the dual NC7WZ04 ultra high speed. The datasheet shows the AC waveform 50% duty cycle
The op amp buffer package size is small small therefore evaluation board needs remodel to get around the microscope level.
A SOIC 8 op amp is a much better choice for op amp however good recommended electrical characteristics and delay propagation.
The Vcc from 1.65V to 6.5V NC7WZ04 buffer has a nice wave form. https://www.onsemi.com/pub/Collateral/NC7WZ04-D.PDF
 
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