6.2 Power supplies and power converters

A power supply is the source of a power domain for a row, and a power converter the source of one for a single product, such as ±6 V made on the back of a module from the bus (6.1). A bus supply feeds the row's bus board with the rails of 6.4: +12 V and −12 V, and +5 V if it provides one. It may be built into an enclosure or sold on its own. The rules below bind every outlet of a supply or a converter, whatever its domain; the limits that differ by domain are in the table at the end of the clause. The 12 V of PWR-DC12 comes from an external adapter, which is outside EIS; a supply that takes it at a DC entry is also a PWR-DC12 product (6.7).

Supplies in the other domains

A power supply may make the 12 V DC rail of 6.7 or the ±6 V rails of 6.8, beside or instead of the bus; it then claims PWR-DC12-OUT or PWR-A6-OUT, publishes the current of each outlet, and meets that domain's outlet rules (SUP-009): PWR-DC12 outlets are DC-BAR21 jacks or DC-VH2 headers, each protected separately (DC-009, DC-012), and PWR-A6 outlets are A6-VH3 within the window of 6.8 (A6-001, A6-002). A claim names each domain the supply gives, power supply (PWR-DC12-OUT) or power supply (PWR-A6-OUT), and each it takes, PWR-DC12-IN for a supply fed from a brick; the direction is in the name, and the claim file carries the figures.

What a supply publishes

A power supply publishes the current it delivers on each rail, in total and at each outlet (PWR-002). It shall publish its ripple and noise on each rail it provides, peak-to-peak, measured as stated below (SUP-001).

Output connector and protection

An output on a plug-and-socket connector, such as a keyed header, a wire-to-board housing, or a DC plug, shall not mate with reversed polarity (SUP-002). An output on individual ¼ in quick-connect tabs or screw terminals cannot be keyed and is exempt; each such terminal shall be marked with its rail (SUP-003).

Each rail shall survive an indefinite short to 0 V without damage (SUP-004). During power-up, power-down, or a fault, no rail shall swing more than one diode drop toward the opposite polarity (SUP-005). At start-up, no rail shall overshoot its nominal voltage by more than 10 % (SUP-006).

EIS · A supply's rails at power-up -12 V -6 V 0 V +6 V +12 V +13.2 V: 10 % overshoot −13.2 V: 10 % overshoot ±one diode drop toward the opposite polarity +12 V rail −12 V rail time from power-on At start-up no rail overshoots its nominal voltage by more than 10 % (SUP-006). During power-up, power-down, or a fault, no rail swings more than one diode drop toward the opposite polarity (SUP-005). Each rail survives an indefinite short to 0 V (SUP-004). The traces are illustrative.

EIS recommends constant-current or hiccup current limiting rather than foldback: a row is a large capacitive load, and a foldback limiter can fail to start into it. EIS recommends bringing the rails up in an order that avoids reverse stress on modules; SUP-005 bounds the reverse swing whatever the order.

Output quality

EIS requires no particular topology. EIS recommends a setpoint within ±1 % and load regulation within ±1 % from 10 % to 100 % load.

Each rail shall have ripple and noise below the limit of its domain (SUP-007):

Domain Ripple and noise, peak-to-peak
The bus below 150 mV Most open-frame switching supplies meet it.
12 V DC — Not set: the adapter that makes it is outside EIS.
±6 V analog below 20 mV For the analog rails a module regulates locally; a linear source is typically under 5 mV.
±15 V analog below 20 mV For the ±15 V analog rails of op-amp circuits that run at the full rail; a linear source is typically under 5 mV.

A linear or post-regulated supply is typically under 10 mV, which suits a row of MOD-VIDEO modules.

Ripple and noise are measured peak-to-peak on each rail at the supply's output terminals, or at test points the product publishes, with each rail loaded at the maker's stated test current, at 20 MHz oscilloscope bandwidth, with a 0.1 µF ceramic capacitor in parallel with a 47 µF electrolytic across the measurement point and a 300 mm (12 in) twisted pair from there to the probe. This is the method common supply datasheets use, so one maker's figure is comparable with another's.

EIS · Measuring ripple and noise supply one rail +12 V 0 V load 0.1 µF ceramic 47 µF at the output terminals 300 mm (12 in) twisted pair oscilloscope, 20 MHz bandwidth peak-to-peak Each rail is loaded at the maker's stated test current and measured at the supply's output terminals, or at test points the product publishes, with 0.1 µF in parallel with 47 µF across the measurement point and a 300 mm (12 in) twisted pair to a 20 MHz oscilloscope. The supply publishes the peak-to-peak figure for each rail (SUP-001); every rail stays below 150 mV (SUP-007). A linear or post-regulated supply, typically under 10 mV, suits a row of MOD-VIDEO modules.

Power converters

A power converter shall publish the heat it dissipates at its rated output and how far it extends behind the product it is mounted on (SUP-008). It publishes the current it takes at its input as every power entry does (PWR-001): for a linear converter on the bus, the output current plus its own. A module sold with an adapter publishes the currents and the depth of the pair. The PWR-A6 converters are in 6.8.

EIS recommends that a power converter's board fit the outline of a 1U module board (5.2.2): a parallel board no taller than 21.10 mm, with the 1U mounting-hole span of 33.65 mm (PANEL-009) behind a 1U panel, so that the same converter can be mounted as a 1U module in a row that has one, or behind the product it feeds.