Author Topic: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit  (Read 6406 times)

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Offline HopWorks

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I absolutely love your videos! Usually, analog+me=fire! but your detailed explanations of the theory has given me confidence, and I have less fires and explosions on my breadboards now. So not only have you helped my understanding of electricity, you have helped to save? the world as well! Hey! Bob's your uncle! Great job and thank you!

It would be nice if you had parts links along with your video's though. I tried searching for an IRF9110 as used in your circuit but came up empty. I found a lot of P-Channel Mosfets, but without a full understanding of Vgs (+-20v???), I can't figure out a replacement.

Anywho... NICE JOB!
 

Offline IanB

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #1 on: December 10, 2012, 11:15:09 pm »
I have less fires and explosions on my breadboards now

 :o

Fires and explosions? Well, electronics for you is certainly more exciting than for most people!
I'm not an EE--what am I doing here?
 

Offline HopWorks

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #2 on: December 10, 2012, 11:40:49 pm »
I have less fires and explosions on my breadboards now

 :o

Fires and explosions? Well, electronics for you is certainly more exciting than for most people!
You have no idea.  :scared:
 

Offline Fezder

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #3 on: March 27, 2013, 07:20:40 pm »
Nice tutorial, easy looking schematics and well explained. BUT, i did of course try this out, 'been looking this kind solution/s for some time. mine version of that first one which has 2 push-buttons, doesn't latch.  it turns on right away, and turns off only the time i hold the off button. i've checked wirings many times, i'm confused what's the problem :D.  i dont know is it because of  incorrect components but here's the list if anyone could lend a hand:...
and sorry if this is NOT the place for asking help :S.
not even SCR equilavent circuit worked, tired that too, same symptoms.
ps: its not the end of the world, but i found couple other latching circuits which i succeeded to get working
supply voltage is 12v
transistors: bc547 / bc557
resistors: both 1k, tried 10k and 100k
load was LED with 1k resistor
Both analog/digital hobbyist, reparing stuff from time to time
 

Offline con-f-use

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #4 on: July 07, 2013, 11:15:29 am »
I can confirm that the first schematic does in fact NOT work with a BC527/537 combination.

Here is what I used for a small ?C-project. It's not pretty but very simple and does the job. The 2N7000 is only rated for 200mA so others might need something beefier. Also it switches ground, which generally is a bad idea, but should be fine for 5V. I don't care about the cap slowly leaking and eventually turning the whole thing off by itself as it never runs more than a day anyway and the circuit gave me not problems.

Additionally because I'm tired of looking, for your convenience here the links to a few spin-offs:
https://www.eevblog.com/forum/beginners/world%27s-simplest-soft-latching-power-switch-circuit-%28modification%29/msg121811/#msg121811
https://www.eevblog.com/forum/projects/two-mosfet-soft-latching-startup-switch/msg167730/#msg167730
https://www.eevblog.com/forum/projects/characteristics-of-a-soft-latch-power-switch/msg152164/#msg152164
https://www.eevblog.com/forum/projects/yet-another-self-latching-mosfet-switch/msg171647/#msg171647
https://www.eevblog.com/forum/beginners/world%27s-simplest-soft-latching-power-switch-circuit-%28modification-2%29/msg121872/#msg121872
https://www.eevblog.com/forum/projects/an-improvement-on-the-soft-latching-power-switch/msg171112/#msg171112
https://www.eevblog.com/forum/projects/mosfet-power-switch-with-auto-off/15/
« Last Edit: July 07, 2013, 11:26:37 am by con-f-use »
 

Offline opty

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #5 on: December 19, 2013, 10:58:37 pm »
In the first circuit PNP's leakage current will immediately pull NPN up.

You could add a resistor (parallel to the off switch)  to prevent it.

 

Offline jimjam

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #6 on: June 14, 2014, 05:51:31 pm »
In the first circuit PNP's leakage current will immediately pull NPN up.

You could add a resistor (parallel to the off switch)  to prevent it.


I just discovered this while breadboarding it :) Why is there a leakage current?
 

Online SeanB

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Re: EEVblog #262 - World's Simplest Soft Latching Power Switch Circuit
« Reply #7 on: June 14, 2014, 05:55:40 pm »
Because real transistors always have some leakage current, so there is leakage. Typically you will add a resistor between base and emitter of both transistors to ensure that they will stay turned off even with a low amount of leakage. In this particular circuit 100k or so will work, as the leakage currents are in the femtoamp region. If you are driving big power devices then you will be much lower in value.

Necromancing the thread..........
 


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