Author Topic: Can adding MCU Powerdown to Soft-Latch Power Switch be simplifed?  (Read 704 times)

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Offline optoisolatedTopic starter

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Hi all,
I've started working on a project that needed soft-latch power switch, and I thought I'd give Dave's simplified Soft-Latch power switch design a go. One of the changes i've added is to add an additional NPN transistor on the base of the first transistor which allows for the MCU to ground it, which should allow it to power down the unit using software, without impacting the operation of the Soft-Latch switch. The MCU is supposed to leave the pin high-impedance when it's not operating so in theory I should be able connect that pin directly (with a low val resistor) to the base of the first transistor, but I opted to add an additional transistor to allow it be a bit more controlled. (Schematic diagram attached)

So my questions are:
1. Have I overcomplicated the design by adding the additional transistor, and
2. Is there a better way to go about adding the option to allow the MCU to ground the base of the first transistor?

Cheers and beers  :-+
Optoisolated
 

Offline optoisolatedTopic starter

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Re: Can adding MCU Powerdown to Soft-Latch Power Switch be simplifed?
« Reply #1 on: March 06, 2020, 12:48:49 pm »
Definitely simpler, not sure about cheaper tho; I can buy 100 2N3904's on eBay for a dollar. The PMOS is the most expensive component and even that would run me about 5c/ea on eBay. I like the idea of a single component to manage the power though; might look into that option some more. Defintely want to avoid having to program one if I can, but I'm sure there's plenty of power switch ICs that come programmed with some common logic. Cheers  :-+
 

Online ataradov

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Re: Can adding MCU Powerdown to Soft-Latch Power Switch be simplifed?
« Reply #2 on: March 06, 2020, 05:41:51 pm »
Here is a much simpler version of this switch that also keeps the button available to the MCU during normal operation - https://github.com/ataradov/siggen/blob/master/hw/siggen.pdf

So MCU can use it to just disable the power (may be after a delay or debouncing), or actually use it for normal device operation. In my case I use it for menu navigation and a long press actually disables the power.

When the button is pressed, the MCU will be powered and it must set PWR_EN high. If it wants to disable the power, just set PWR_EN low.

When MCU is powered, the state of the button is read on BTN_C.
« Last Edit: March 06, 2020, 05:47:39 pm by ataradov »
Alex
 
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Online SiliconWizard

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Offline optoisolatedTopic starter

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Re: Can adding MCU Powerdown to Soft-Latch Power Switch be simplifed?
« Reply #4 on: March 06, 2020, 10:22:35 pm »
That's definitely simpler.. I like it! :-+
 


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