PSU Protections - What do they help against and how do they work?

[LukeSavenije]

Introduction

There are many things you should look for on a PSU, and subjectively protections are one of the most important, if not the most important thing to look for. They will shut down the PSU down because of too much power, too much or too little voltage, short circuits or high temperatures. Here will be a breakdown of every protection. What they do, how they technically work and how important it is.

 

Some terms used

Protection IC= an integrated Circuit that monitors the PSU, integrating most, and in some cases all protections.

ATX Standard= A standard set by Intel with all the requirements or recommendations for PSUs in regard of protections, voltage regulation, ripple and so on. 

Shunt resistor= a device which creates a low-resistance path for electric current, to allow it to pass around another point in the circuit. This way it can measure current

Thermistor=A type of resistor whose resistance is dependent on temperature.

 

OPP (Over Power Protection)

Over Power Protection or OPP is a protection that will shut down the PSU when too much power is pulled, generally this is between 110 and 140% of the advertised wattage. This is a protection that works as a limit, shutting down when a certain point is reached, but doesn't actively monitors the amount of current.

 

It's generally integrated into the PWM controller and is a crucial protection. It's required in ATX except if OCP is also there.

 

OCP (Over Current Protection)

Over Current Protection or OCP has the same purpose, but a different concept as OPP. OCP will generally be faster than OPP, since it uses shunt resistors to check the amount of current, and will shut down if a certain point is reached. OCP on 12v is generally only found on PSUs with multiple rails, since OPP can handle a single rail just fine.

 

It's generally integrated into the protection IC combined with shunt resistors and is a recommended, but not required protection by ATX.

 

OTP (Over Temperature Protection)

Over Temperature Protection or OTP is a protection that protects the PSU against overheating with for example a fan failure. it's generally a thermistor combined with a protection IC that supports this, but there have also been cases where it was integrated into the fan controller. Most reviewers stop measuring after 200c, but it depends on the place the thermistor is integrated what recommended limits are.

 

It's recommended until ATX 2.52, but since has been required.

 

UVP (Under Voltage Protection)

Under Voltage Protection or UVP is meant to shut down if voltage goes down too far. not only because a lot of components need a stable voltage, so you can have less correction on the VRM side, it's also there because OCP and OPP measure by how much current is going through, but not the voltage. so if the voltage drops down, the current can go higher, which can result in burnt cables or connectors.

 

It's generally integrated into the protection IC, and recommended in the ATX standard, but required for a modern PSU in my eyes.

 

OVP (Over Voltage Protection)

Over voltage Protection or OVP works to a similar way as UVP, but the other way around. It checks the voltage on a rai that it isn't getting too high, so it can keep a safe height, and will shut down if it gets too high.

 

It's generally integrated integrated into the protection IC and required by ATX standards.

 

Voltages for OVP according to ATX spec

Output	Minimum (V)	Nominal (V)	Maximum (V)
+12 VDC	13.4	15	15.6
+5 VDC	5.74	6.3	7
+3.3 VDC	3.76	4.2	4.3
5VSB	5.74	6.3	7

 

SCP (Short Circuit Protection)

Short Circuit Protection or SCP measures the resistance on each rail, and will shut down when resistance is lower than 0.1 Ohms. Generally this goes combined with OPP, OCP, OVP and UVP.

 

It's generally integrated into the protection IC, and is required on ATX spec, with separate circuits per rail.

 

PWR_OK Signal

The Power Good or PWR_OK signal is a delay signal to show if the PSU has enough energy stored for at least 17 ms under maximum load. This delay must be under 500ms, but is preferred below 250ms according to the ATX specification, but must be higher than 100ms.

 

Verdict 

OPP is required, for when too much power is pulled.

OCP is recommended, and is meant for the same thing.

OTP is required since the most recent ATX specification when too high temperatures are reached.

UVP is recommended by ATX, required by me for when voltage drops too low

OVP is required by ATX for when voltage goes too far up.

SCP is required for when resistance gets too little.

PWR_OK is required to signal the PSU can still function right until the next one.

 

Sources

https://en.wikipedia.org/wiki/Thermistor

https://en.wikipedia.org/wiki/Shunt_(electrical)

https://www.tomshardware.com/reviews/power-supplies-101,4193.html

https://www.intel.com/content/dam/www/public/us/en/documents/guides/power-supply-design-guide-june.pdf

[Fasauceome]

ICP? (and no, not insane clown posse)

[LukeSavenije]

Just now, Fasauceome said:

ICP? (and no, not insane clown posse)

inrush current protection is more a limiter than a protection, honestly

[Fasauceome]

Just now, LukeSavenije said:

inrush current protection is more a limiter than a protection, honestly

so it more or less boils down to having an inductor

[BlackManINC]

Looks like 'PWR OK Signal' is the only protection my PSU doesn't have. 

 

 

[LukeSavenije]

19 minutes ago, BlackManINC said:

Looks like 'PWR OK Signal' is the only protection my PSU doesn't have. 

 

 

every psu has a PWR OK signal... accurate or not

[BlackManINC]

1 hour ago, LukeSavenije said:

every psu has a PWR OK signal... accurate or not

Hmm, G.Skill doesn't list it on my power supply for some reason. I guess it doesn't have to because its a default item. 

[jonnyGURU]

On 2/10/2020 at 9:58 AM, LukeSavenije said:

OPP (Over Power Protection)

Over Power Protection or OPP is a protection that will shut down the PSU when too much power is pulled, generally this is between 110 and 140% of the advertised wattage. This is a protection that works as a limit, shutting down when a certain point is reached, but doesn't actively monitors the amount of current.

 

It's generally integrated into the protection IC and is a crucial protection. It's required in ATX except if OCP is also there.

 

OTP (Over Temperature Protection)

Over Temperature Protection or OTP is a protection that protects the PSU against overheating with for example a fan failure. it's generally a thermistor combined with a protection IC that supports this, but there have also been cases where it was integrated into the fan controller. The absolute limit of it should be below 200c, but it depends on what part of the PSU it's integrated.

 

It's recommended until ATX 2.52, but since has been required.

OPP:  Not part of protection IC, part of PWM controller.  

 

OPP is on AC side.  OCP is on DC side.  PWM controller is on AC side.  Protection IC is on secondary side.

 

OTP:  I'd remove the "absolute limit" reference because the temperature is going to completely depend on where the measurement is being taken.  Besides:  200°C is way too hot for ANY part inside a PSU.  

[BlackManINC]

6 minutes ago, jonnyGURU said:

OPP:  Not part of protection IC, part of PWM controller.  

 

OPP is on AC side.  OCP is on DC side.  PWM controller is on AC side.  Protection IC is on secondary side.

 

OTP:  I'd remove the "absolute limit" reference because the temperature is going to completely depend on where the measurement is being taken.  Besides:  200°C is way too hot for ANY part inside a PSU.  

I can't imagine 200°C being tolerable for most any product you can get from a retailer. 

[LukeSavenije]

9 minutes ago, jonnyGURU said:

OTP:  I'd remove the "absolute limit" reference because the temperature is going to completely depend on where the measurement is being taken.  Besides:  200°C is way too hot for ANY part inside a PSU.  

it's the temperature Aris stops measuring, but the rest you're about right with... I'll edit some changes in soon

[jonnyGURU]

1 hour ago, LukeSavenije said:

it's the temperature Aris stops measuring, but the rest you're about right with... I'll edit some changes in soon

Where is HE measuring that?  Doesn't sound right.  

 

When I do thermal testing, I have 37 thermal probes attached to different components of the PSU (not including also measuring intake, exhaust and ambient, which is also measured).

 

The highest I ever see that's a pass is 100° to 110°C from thermistors applied directly to one of the primary MOSFETs.   

[LukeSavenije]

3 minutes ago, jonnyGURU said:

Where is HE measuring that?

an example you can see here: https://www.tomshardware.com/reviews/thermaltake-toughpower-grand-rgb-850w-gold-psu,5822-6.html

 

I'm not talking about what should be set, but rather to how high i've seen testing goes. indeed depending on the spot 160 can already be too high

[jonnyGURU]

6 minutes ago, LukeSavenije said:

an example you can see here: https://www.tomshardware.com/reviews/thermaltake-toughpower-grand-rgb-850w-gold-psu,5822-6.html

 

I'm not talking about what should be set, but rather to how high i've seen testing goes. indeed depending on the spot 160 can already be too high

No.  I would not go by that.

 

I think he's saying if it goes over 200°C it's a hard fail, but I'm telling you that if it gets anywhere near that, that PSU has already exploded.  

 

I'll talk to Aris about that.

 

[LukeSavenije]

3 minutes ago, jonnyGURU said:

I think he's saying if it goes over 200°C it's a hard fail, but I'm telling you that if it gets anywhere near that, that PSU has already exploded.  

stupid question maybe... do you have some estimated limits for a couple common locations i could use? that might make it more clear for people

[jonnyGURU]

23 minutes ago, LukeSavenije said:

stupid question maybe... do you have some estimated limits for a couple common locations i could use? that might make it more clear for people

So... Obviously every PSU gets it's own thermal test report, but those vary from model to model because different components used have different tolerances. There's no hard pass/fail.   A test report from a VS is going to be vastly different than a test report for an HX.

 

But I will say, nothing is a pass at 200°C.