Timeline for wiring 555 to disconnect itself from electricity
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
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| Jan 18, 2015 at 20:12 | comment | added | Vladimir Cravero | @Not_Important just stick to the top answer, my circuit doesn't work. | |
| Jan 18, 2015 at 19:31 | comment | added | Not_Important | @Vladimir Cravero thanks alot for help so far but I dont rly understand everything here What is the diode youre reffering to, is it the one in transistor? I dont see protection diode inside a 555 chip Should I use a cap, otherwise my circuit wont reliably work? | |
| Jan 18, 2015 at 19:22 | comment | added | Vladimir Cravero | @SpehroPefhany I've seen the schematic and now I understand, you are perfectly right. Maybe a cap between R1 and R2/base can make this thing work... Or oscillate. That might be the most unusual way of building an oscillator with a 555. Thanks for using your time to help me. | |
| Jan 18, 2015 at 19:05 | comment | added | Vladimir Cravero | @SpehroPefhany now I want to understand what you mean. You are speaking of a Vce junction (?) from output to ground, while you should need some Vcc to turn Q1 back on, I'm completely lost. This might be a new question though | |
| Jan 18, 2015 at 18:56 | comment | added | Spehro 'speff' Pefhany | There is an isolation diffusion that will become forward biased, similar to a "protection diode" in a CMOS chip. Even if you don't believe me, a quick look at the schematic will tell you that the best case is a 4.7K series with 220 ohms series with a forward-biased Vce junction from output (negative) to GND. That will turn the transistor on easily, even with R2. | |
| Jan 18, 2015 at 18:52 | comment | added | Vladimir Cravero | I meant that some current can flow through the protection diodes. | |
| Jan 18, 2015 at 18:50 | comment | added | Not_Important | 555 might get power from protection diodes?? obviously diodes are passive element | |
| Jan 18, 2015 at 18:35 | comment | added | Vladimir Cravero | As Olin said and as I quoted: you can't control a circuit power with an emitter follower. My solution, as well as Spehro, uses transistor(s) in common emitter configuration, and that can work. | |
| Jan 18, 2015 at 18:32 | comment | added | Not_Important | but why does my "design" not work ive spent hours on trying to figure it out | |
| Jan 18, 2015 at 18:29 | history | edited | Vladimir Cravero | CC BY-SA 3.0 |
edited body
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| Jan 18, 2015 at 18:24 | comment | added | Vladimir Cravero | leaving them floating is precisley what you want to do since you want to turn off the IC. | |
| Jan 18, 2015 at 18:20 | comment | added | Not_Important | im no expert but wouldn't i have to place a big pull up resistor from Vcc to GND pin because otherwise I'd make Trigger and GND pin "floating"? | |
| Jan 18, 2015 at 17:59 | history | answered | Vladimir Cravero | CC BY-SA 3.0 |