# Rack power conversion and distribution

Canonical: https://semiaifoundry.com/learn/atlas/rack-power-conversion/
Revision: 2026-10-07
Rights: https://semiaifoundry.com/ai-atlas/licenses.html

Data-center physical systems · Atlas v1.3.0

# Rack power conversion and distribution

Moves electrical energy from facility supply through conversion stages to low-voltage chip rails.

[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#rack-power-conversion)Chip voltage rails to facility heat rejection

Learning objectiveDistinguish conversion losses, redundancy and measured consumption.

## The mechanism

Facility electricity reaches a rack through distribution equipment and power supplies, then travels through busbars, board connections and local voltage regulators. Each stage has a voltage, current, capacity and conversion efficiency. The DGX GB reference describes power shelves converting AC to nominal rack DC, but other racks use different arrangements. Nameplate capacity includes redundancy and does not equal measured consumption. At the chip, low voltage implies high current for a given power, increasing the importance of short, low-resistance paths. A power value needs a measurement location before it can constrain compute capacity: input conversion losses and downstream IT demand belong to different boundaries.

1.  Mark every conversion stage and its electrical measurement boundary.
2.  Calculate current from power and voltage for the path being evaluated.
3.  Apply stage efficiency once and account for the associated local heat.
4.  Check redundancy and operating headroom separately from normal workload draw.
5.  Verify final rail quality and rack acceptance under representative load changes.

## Science and assumptions

### Conversion accounting

$$
P_{\mathrm{out}}=\eta P_{\mathrm{in}},\qquad I=\frac{P}{V}
$$

Output power equals conversion efficiency times input power. At the selected DC boundary, current is power divided by voltage.

Symbols and units

P\_out

Power leaving the conversion stage

W

η

Stage conversion efficiency

fraction

P\_in

Real power entering the conversion stage

W

I

Current at the selected DC boundary

A

P

Power at that same DC boundary

W

V

Nonzero voltage at that boundary

V

Power is watts, η dimensionless efficiency, current amperes and voltage volts.

Assumptions Steady average values at a specified stage; AC power factor and transient behavior need additional treatment.

## Engineering example

Synthetic regulator: supplying 1 kW at 1 V requires 1,000 A on that rail. At 90% efficiency its input is about 1.11 kW, leaving about 111 W of conversion loss to remove.

## Distinctions and tradeoffs

Adding PSU nameplate ratings does not establish typical rack power, especially when supplies provide redundant capacity.

Higher distribution voltage reduces current for a given power, while conversion close to the chip adds efficiency and thermal requirements.

Accelerator deployment needs suitable distribution and regulation, not only enough annual electricity or enough power-supply labels.

## Specifications and interfaces

Power boundary

Facility input, rack input or chip rail

Do not compare values from different locations as equivalent.

Capacity versus draw

Installed PSU rating versus measured load

Redundant supplies provide resilience and headroom, not automatic consumption.

### Interfaces

Facility electrical feed Input

AC power under distribution and redundancy constraints

Chip voltage rails Output

Regulated DC with conversion losses and transient limits

## Check your understanding

### Why does a low-voltage rail require large current at high power?

1.  Low voltage creates energy
2.  Current and voltage are the same quantity
3.  Power equals voltage times current

Answer and reasoning

Power equals voltage times current

For fixed delivered power, reducing voltage increases the required current and its associated distribution challenges.

## Evidence and scope

The numeric example is not a product rail specification. Documented rack DC and approximate rack power are source-scoped in the claims ledger.

No current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.

## Sources

-   [NVIDIA DGX GB Rack Scale Systems: Hardware](https://docs.nvidia.com/dgx/dgxgb200-user-guide/hardware.html)

[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/rack-power-conversion-594556674a19ceb6.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)

## Continue exploring

### Foundations

-   [Power supply and power shelf](https://semiaifoundry.com/learn/atlas/power-supply/)
-   [Voltage regulator module](https://semiaifoundry.com/learn/atlas/voltage-regulator/)

### Related lessons

-   [Rack power shelf and DC busbar](https://semiaifoundry.com/learn/atlas/power-shelf/)
-   [Power integrity and transient voltage margin](https://semiaifoundry.com/learn/atlas/power-integrity-budget/)