Discussion what exactly is the point of a digital PSU?

[Order 66]

I have heard that a digital PSU provides better power regulation, but what exactly does that mean, and how does it do it? What are the advantages of a digital PSU? I have also noticed that digital PSUs are not cheap.

 

[kira-faye]

It's a different (more efficient and accurate) method of voltage regulation. Costs more to build, though that probably won't be the case forever. You're better off googling the details than me trying to explain it here.

 

[Order 66]

It's a different (more efficient and accurate) method of voltage regulation. Costs more to build, though that probably won't be the case forever. You're better off googling the details than me trying to explain it here.

I have already tried googling it, but I don't really understand the details. Hence the point of me starting the thread.

 

[Eximo]

Yes, that gets pretty technical.

But a more traditional power supply basically just has capacitors, transformers, and these days voltage regulators. So you take high voltage AC, across a Bridge Rectifier to get pulsed all positive AC, run that through the main capacitors to smooth it out and get closer to a flat voltage. For the US that would end up around 170 volts. Then you run that through a transformer to bring that down to 12V, 5V, 3.3V. Newer power supplies pretty much do the lower voltages with regulators which is more efficient, since the power output required on the low voltages is rather low these days.

Older PSUs actually react badly when hooked up to a modern system, since the load on the 5V ends up being too low, it messes with how the 12V gets produced, resulting in higher voltages if memory serves.

Digital PSUs use more complex computer controlled feedback loops to regulate current and produce a more stable voltage. Basically they can be very reactive to changing loads and maximize efficiency at a given load.

 

[Order 66]

Yes, that gets pretty technical.

But a more traditional power supply basically just has capacitors, transformers, and these days voltage regulators. So you take high voltage AC, across a Bridge Rectifier to get pulsed all positive AC, run that through the main capacitors to smooth it out and get closer to a flat voltage. For the US that would end up around 170 volts. Then you run that through a transformer to bring that down to 12V, 5V, 3.3V. Newer power supplies pretty much do the lower voltages with regulators which is more efficient, since the power output required on the low voltages is rather low these days.

Older PSUs actually react badly when hooked up to a modern system, since the load on the 5V ends up being too low, it messes with how the 12V gets produced, resulting in higher voltages if memory serves.

Digital PSUs use more complex computer controlled feedback loops to regulate current and produce a more stable voltage. Basically they can be very reactive to changing loads and maximize efficiency at a given load.

I thought in the US it was 120 volt.

 

[Eximo]

I thought in the US it was 120 volt.

Common misconception. 120V or 115V RMS. In reality that is a approximately 169 volts positive, 169 volts negative with a roughly 60hz sine wave. When you take the integral of that you end up with the area under the sine wave, the average (or Root Mean Square) specifically comes out to 125 VAC or so.

That is why the typical capacitors in a PSU are 400V, so they can handle that and the typically higher AC voltages in Europe, which comes out to around 340 volts after rectification.

 

[Eximo]

I have already tried googling it, but I don't really understand the details. Hence the point of me starting the thread.

You need a pretty decent background in electronics to really grasp it outside of a layman's explanation. I have a decent electronics background and I don't really know how they work in detail. I would have to sit down and research it a while.

But the basic principles are there. You have a variable current load on a voltage source and that is fairly tough to keep perfect efficiency at all power points. One of the reasons you size a PSU to the job, they have an efficiency curve where they work best.

A digital PSU can do a lot to compensate for that, and the load doesn't make a big difference to the overall efficiency.

 

[Order 66]

You need a pretty decent background in electronics to really grasp it outside of a layman's explanation. I have a decent electronics background and I don't really know how they work in detail. I would have to sit down and research it a while.

But the basic principles are there. You have a variable current load on a voltage source and that is fairly tough to keep perfect efficiency at all power points. One of the reasons you size a PSU to the job, they have an efficiency curve where they work best.

A digital PSU can do a lot to compensate for that, and the load doesn't make a big difference to the overall efficiency.

is there a cheap (sub $200) digital PSU? I know that Corsair makes one, but AFAIK it is more than $200. I do not have any kind of electronics background, hence the reason for starting this thread in hopes of a simple explanation.

 

[Eximo]

One of those things where you need to sit in front of an oscilloscope as the individual components are added so you can see the effects. And that is just for the rectification part. Then there are all the circuits for surge protection, over voltage protection, over current protection, etc. Those are mostly analog, but you pretty much won't find a PSU these days without some digital component.

Digital PSUs have the same rectification to get the source voltage. After that it is all digital voltage and current regulation. When I say loops I am talking about a logical algorithm that controls the output based on voltage and current sensing circuits. To get all that feedback is what costs the money, then having circuits strong and fast enough to deliver 10-100s of AMPs on command while maintaining a strict voltage.

I think we don't see them much because the market is small. They are expensive and only make sense for high level enthusiasts.

 

[stonecarver]

It might seem like its off topic but if you read about Digital amplifiers the understanding bleeds over digital computer power supplies. The digital part in a digital amplifier is its power supply. The amp section is still a class A/B.
I have the Amplifier below in the collection.

One example is the Sunfire 300 Amplifier. Digital amps are common today but if you can find all the older wright up's on 1990 digital amps they went to great lengths to explain it in layman's terms how the digital power supply works vs conventional.

Product Review - Sunfire Power Amplifier

The Sunfire amplifier represents the third generation design from Bob Carver (the first generation being at Phase Linear, the second at Carver Corporation, and now the third at Sunfire Corporation).

hometheaterhifi.com