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5V, 3A over-voltage circuit needed

AndrewCRA

Sep 23, 2022
2
Joined
Sep 23, 2022
Messages
2
Hi all,

I have been trying a few different approaches over the last week in an attempt to create a circuit to "safely" supply power to my NVIDIA Jetson Nano.

The issue arose when I realized that a voltage regulator I was switching with an n-channel mosfet, is actually switching through the VIN t VOUT, when
the ground is floating. Since then I have been using an n-channel to switch a p-channel mosfet that then switches the positive voltage.

Having nt yet felt comfortable enough to supply voltage this way to my (precious) Jetson Nano, I'm looking for an alternative, secondary circuit to ensure the voltage getting through never
exceeds the safe voltage range of 5.2V max.

The approaches I have taken are:

1. Built a circuit similar to the one in this image:
https://www.maximintegrated.com/content/dam/images/design/tech-docs/760/di66fig01.gif
However this does have a limitation on the power that can be switched. My Jetson Nano requires about 2.5A during normal operation.
So a circuit being capable of switching currents of up to 3.5A is needed.
For a while I have been testing a similar circuit with some of the BJTs I have available. I have tried multiple variations of the circuit using both NPN and PNP transistors and a mix thereof in conjunction with a zener diode 5.1V to realize this circuit.
(BC557, BC558, 2N2222, 2N3904, BC547, BC549)
What I have noticed is that I needed about 8V before I was able to get the diode to get conductive in the opposite direction and switch the transistor stage.

2. I have also come across the circuit below, using a triac. I have not been able to give this a try yet, as I'm waiting for parts (4 weeks and counting).
https://www.instructables.com/Over-Voltage-Protection-for-5V-Circuits/

My question to experts in this forum is, do you have knowledge or insight into a circuit, that can achieve over-voltage protection, switching off at voltages > 5.1V, while still being able to switch a load (ideally positive switching) of about 3A?
The following components are available, I just have no clue how to make a viable circuit and after spending more than a week trying on a breadboard, I finally have come to my senses.
BJT's:
24 value standard NPN/PNP transistor assortment with most common BJTs (such as BC517, 547, BC549, BC556, BC557, BC558, S-series, 2N-series, A nd C-Series)
MOSFETs:
IRF1405 n-channel
ZT2467 p-channel

Zener Diodes: 5.1V
Resistors (all sorts)



Please let me know what information is needed, or maybe you even have a schematic from a past similar circuit!?

Thank you!
 

kellys_eye

Jun 25, 2010
6,514
Joined
Jun 25, 2010
Messages
6,514
If you are using a quality 5V supply source (which, given your application, you should be) then your apprehension is over-stated.

Personally I'd purchase a quality 5V supply (one that does the supply rail monitoring itself) and leave it to do what it does best - i.e. work. You can end up worrying about the protection circuitry not working and developing protection for the protection circuitry ad-infinitum.

As ever Sh17 happens but if you spend all your time worrying about it you'll be staring at non-working Jetson Nano for fear of never turning it on.
 

danadak

Feb 19, 2021
751
Joined
Feb 19, 2021
Messages
751

AndrewCRA

Sep 23, 2022
2
Joined
Sep 23, 2022
Messages
2
Hi Guys,
Thanks to both of your for your answers.

@kellys_eye
I must clarify that the application is mobile and battery powered, so wall outlet power supplies are not applicable. I have already designed a custom circuit board and figured for the (important) voltage regulator part, to use a dedicated DC/DC converter module.
Like this one from Ali-Express: https://www.aliexpress.com/item/1005001703274616.html
(DC/DC 12V 24V Step Down to 5V 5A 25W Voltage Buck Converter Regulator Transformer for Car Truck Vehicle)

Initially I thought of using a Linear Voltage Regulator similar to 7805. However I didn't want to waste my battery charge away in heat, especially coming down from a 4S (16.8V at full charge) Battery assembly.

So I'm looking for a circuit using parts that are readily available (chip shortage non-sense) that I can use to design a small circuit board as an add-on for this application and also use the design as a reference for future circuit designs, to directly built it in.

@danadak
I have been looking at the High SIde switches and diagnostic IC's. However, they seem to require an external controller by the looks of it, which also requires a power source. So it can't be used to power the mcu itself, as the mcu needs to have power to tell the High-Side Switch what to do.
In either case, I'm more after a very simplistic design, that is directly in-between the output of the 5V, 5A regulator and the device, ensuring the voltage never goes above 5V.
 

danadak

Feb 19, 2021
751
Joined
Feb 19, 2021
Messages
751
You mention in original post losing the reference leg to ground of a regulator.

One classic approach is blow a fuse with a crowbar, scr, that shorts supply rail
to ground if V exceeds a design set value. The crowbar can operate off the
downstream power (while it exists) to generate the trigger and the SCR turns
on and will not turn off until certain conditions are met.


1663972758344.png


You could use it to trip a breaker, then use another circuit to reset breaker
when power is restored.

All simple analog circuits, of course a micro would do this better overall.
Especially as related to timed recovery issues.

You could use a shunt regulator that i=kicks in at over V and draws more current
relying on V drop the source experiences with incred loads. This has a number
of issues, undesirable side effects, but is possible.....

Regards, Dana.
 
Last edited:

Sunnysky

Jul 15, 2016
541
Joined
Jul 15, 2016
Messages
541
Hi all,

I have been trying a few different approaches over the last week in an attempt to create a circuit to "safely" supply power to my NVIDIA Jetson Nano.

The issue arose when I realized that a voltage regulator I was switching with an n-channel mosfet, is actually switching through the VIN t VOUT, when
the ground is floating. Since then I have been using an n-channel to switch a p-channel mosfet that then switches the positive voltage.

Having nt yet felt comfortable enough to supply voltage this way to my (precious) Jetson Nano, I'm looking for an alternative, secondary circuit to ensure the voltage getting through never
exceeds the safe voltage range of 5.2V max.

The approaches I have taken are:

1. Built a circuit similar to the one in this image:
https://www.maximintegrated.com/content/dam/images/design/tech-docs/760/di66fig01.gif
However this does have a limitation on the power that can be switched. My Jetson Nano requires about 2.5A during normal operation.
So a circuit being capable of switching currents of up to 3.5A is needed.
For a while I have been testing a similar circuit with some of the BJTs I have available. I have tried multiple variations of the circuit using both NPN and PNP transistors and a mix thereof in conjunction with a zener diode 5.1V to realize this circuit.
(BC557, BC558, 2N2222, 2N3904, BC547, BC549)
What I have noticed is that I needed about 8V before I was able to get the diode to get conductive in the opposite direction and switch the transistor stage.

2. I have also come across the circuit below, using a triac. I have not been able to give this a try yet, as I'm waiting for parts (4 weeks and counting).
https://www.instructables.com/Over-Voltage-Protection-for-5V-Circuits/

My question to experts in this forum is, do you have knowledge or insight into a circuit, that can achieve over-voltage protection, switching off at voltages > 5.1V, while still being able to switch a load (ideally positive switching) of about 3A?
The following components are available, I just have no clue how to make a viable circuit and after spending more than a week trying on a breadboard, I finally have come to my senses.
BJT's:
24 value standard NPN/PNP transistor assortment with most common BJTs (such as BC517, 547, BC549, BC556, BC557, BC558, S-series, 2N-series, A nd C-Series)
MOSFETs:
IRF1405 n-channel
ZT2467 p-channel

Zener Diodes: 5.1V
Resistors (all sorts)



Please let me know what information is needed, or maybe you even have a schematic from a past similar circuit!?

Thank you!
5V @ 3A is a trivial supply issue. But you have yet to define all the loads. It makes a difference if you have inductive or motor loads and datasheets are needed. LEDs are easy to drive. You are asking for a bandaid to a poor supply problem rather than fixing the supply requirements. Please detail the problems not your challenges. Also, indicate what parts or suppliers you are limited to and the quantity required. In the meantime, I'm sure you have an old PC PSU with 5V @ 25A at least.
 
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