PC104p-PWR28

PC104pPWR28 power supply provides for the +5V, +3.3V, +12V, minus 12V and minus 5V from a "28V" supply, battery etc. Each rail is protected with "self-healing" fuses. The supply uses switching technology to provide high efficiency coupled with low pass filtering to provide low noise and fast response to transient loads. The handy locking screw terminal style connector allows discrete wiring solutions within the chassis. The mating connector and 12" cable are included with the PC104pPWR series. PC104pPWR28 is intended to work with a 14V-34V input. For 12V applications please see PC104pPWR12.

Aircraft and other systems use "28V" power to operate equipment. PC104pPWR28 has a wide input range to operate with 14 - 34 V power. The reference power is converted to 12VDC. The 12VDC is fuse protected and tied to the PC104 stack connections. The pre-fuse 12V power is also connected to the 5V, 3.3V, -5V and -12V power supplies.

Power is routed from the power supplies to connectors with mini-planes each of which is rated for more than the maximum draw. The total power dissipation is limited to the external power supply capabilities. Each rail can draw to the maximum to cover situations where the power utilization is not balanced. 8/10A max current on 5V, 8/10A max current on 3.3V, 4A max current on -12, 4A from +12V, 4A max on minus 5V. The VIO is selected from the 3.3 or 5V supply and is included in the 8/10A available on those rails. Please note that special builds can be done to remove unused power supplies for your production requirements. Please also note that the +/- 12V and -5V supplies are limited by a single pin on each connector for those voltages per the specification. The stack pins can handle slightly more than 1A under most conditions.

The maximum rating is based on room temperature. The power supply components are all rated for 85C or higher ambient temperature. The fuses in particular have a curve which derates over temperature. At 23C the fuses "hold" rating is set to handle the maximum designed draw. For example 10A on a revision C 5V rail. At 60C the fuse hold figure derates from 2.5 to 1.65 leading to a potential max current of 6.7A at 5V at an ambient of 60C. [1.65 *2 fuses * 12V * .85 / 5]. In practice the hold is the guaranteed current that will pass at a given temperature and the trip is the guaranteed trip current at a given temperature. Somewhere between the hold and the trip is the point where the fuse will actually trip. This means, in most cases with the trip 2x the hold, the power supply will continue to deliver full power up through 60C ambient, but can´t be guaranteed beyond the hold value. Also the efficiency number of 85% is very conservative and it is more likely that 90+% would be achieved at full load which will also increase the available current.

The 12V supply is designed to source 18A = 216 Watts. At max theoretical load 199 W are sourced by the secondary supplies. In reality the 12V, -12V, and -5V circuits will not be loaded to 4A since the PC104p stacking pins can't handle that much current. The 12V power supply will run at something closer to 50% providing plenty of margin over temperature.

The +12V rail is powered up first followed by the -12V and -5V power rails and finally the 3.3 and 5V power rail. The rails are delayed relative to one another to reduce the inrush current requirement. The 12V rail is used to power the -12V and -5V rails leading to a delay based on the rise time of the 12V and inherent delay of the downstream supplies. The 5V and 3.3V supplies have a voltage supervisor circuit triggered from the 12V to delay the start-up of these supplies by several mS.

The reference voltage is connected to the power supply through a right angle connector. PC104pPWR28 has a right angle board mount connector. The cable side is also right angle for convenient cable routing in your chassis. Two 28V, and two ground pins are used to allow for a flexible cable internal to the PC104 chassis. Each pin can handle the full rated load at the lowest voltage providing at least 50% margin in the power path.

The mating connector and a 12" long 20 AWG cable are included with the PC104pPWR28 for easy connection to your power connector. Please contact us for longer or shorter wire lengths or termination to the power connector of your choice.

LEDs are provided on the 3.3, 5V, +12V, -12V and -5V rails for an easy visual check.

PCI VIO is programmable allowing 5V or 3.3V PC104p cards to be used. Many PC104p and PCI-104 cards are "universal" and can work with 3.3 or 5V PCI definitions. A shunt is provided for the user to select 5V or 3V operation. The shunt or open definitions are in the silk-screen for easy reference.

For chassis with Fans installed the PC104pPWR28 has 4 fan power positions available to provide an easy to connect to source for the fans. The 2 pin headers or direct wire connections can be made to the fans; it is envisioned that the rear surface of the power supply would be used to provide a direct path to the fans. With Revision C you have a choice of 5V or 12V power for the Fans. The power is fuse protected with a total of 2A across the 4 connectors. The power is included in the 5V or 12V power budget. Please note PC104p-Chassis has an air-cooled option that is designed to work with the fan power option.

For conduction cooled situations PC104pPWR28 is designed with heavy copper planes to both distribute the power and to distribute the heat. The 4 mounting positions are tied directly to the (2) 4 oz ground planes for good thermal contact. The PC104p-Chassis is designed to use the mounting hardware to route the thermal load to the end plates and then to the chassis wall via thermally conductive vibration damping springs.

Power capabilities and requirements are determined by the client´s situation. PC104pPWR28 can supply the maximum power on each rail as specified above with certain limitations. Please see the manual for a more complete discussion. The basics are that the input power must exceed the output power plus the power consumed by the power supply. The "Power28" design is very efficient with better than 90% efficiency at most loads. For example with 8A on the 5V rail 40W of output power are desired. 40/.81 = 49.4 W input power required. At 28V 1.76A would be required [steady state]. At 14V, 3.52 A would be required. The input current should be calculated based on the required output power consumed and reference voltage. The first stage of the power supply converts from the reference voltage to 12V. The 12V is used to power the secondary supplies. The 12V current is limited to 18A max. 49.4/12 => 4.11A which is well under the limit for the 12V. Please note that the 12V rail has only 1 conversion and can be calculated based on 90% efficiency for higher loads and 85% for lower loading situations.

Testing:
Extensive load testing has been done both on the bench and in the PC104p-Chassis . 2 hours at each load with temperature at FETs, 5V, 3V, +12, -12, and -5V measured and recorded plus current from 28V supply and room temperature. Loads in 1A steps. Tested with closed short chassis no fans [other than on load boards], closed chassis with internal circulation fans, and air cooled chassis configurations. All testing performed on bench top at room temperature with minimal [if any] air flow unless noted, and little conduction to bench [standard ESD bench top tends to be a pretty good insulator] Revision A boards with modifications to allow for up to 9.5A on 5V and 3.3V rails. With Revision C boards new FETs with "PowerPak" footprints are incorporated along with other layout changes which will enhance the load limits under all conditions.

In a fan-less still air situation using a sealed 7 slot version of PC104p-Chassis approximately 40W can be supplied [to the load] maximum continuous at room temperature. With external air blowing across chassis an additional 15-20C is achieved.

With the addition of an internal fan board [2 x 40 mm 12V fans(2)] and sealed 11 slot chassis, in still air, a maximum of 64W is achieved. 12V(.22A), 5V(7.4A), 3.3V(2.2A), -5V(1A), -12V(1A). Please note that the chassis is hot to the touch in this configuration. With External air flow the internal temperature at the hottest component shifts from 74C to 55C - simple blow across the box test. Please note: Industrial temperature parts with an ambient of 85C or higher are standard. Measuring at the surface of the FET provides a very conservative limit.

In the air-cooled configuration: 11 slot chassis, dual 12V fans mounted at chassis rear plate, dual openings at front plate the loading can be increased. 12(.22A), 5(9.4A), 3.3(7.7A), -5(1A), -12V(2A). [104W] At 25C room temperature, Hottest part was 66C. Max rated is 85C air temp - using for conservative component temperature leaves ~20C margin or an operating range of up to 40C or so at this load level. The 12V supply can handle more than 1A, but we only loaded with the two fans. PC104p-COOL can be added to the stack to provide fan based cooling. The COOL card has "Zero Slot" technology to allow direct insertion without adding requirements for additional spacers etc.


Revisions:
Rev A : Initial design with SO8 pkg FETs with the testing results shown above. 5V & 3.3V @8A std.
Rev B PowerPak FETs and upgraded to handle higher current with less cooling. Fuses for 3.3 and 5V moved to be upstream of the regulators to allow for better voltage regulation with increased loads.
Rev C Fuse selection for 5V or 12V fans, layout changes for improved performance. 5V & 3.3V @10A std.
Rev D/A Combined fab for both 12V and 28V versions [build option] renumbered and restarted at RevA. Add Voltage Monitors.

If you have custom requirements please call or e-mail us with the details.
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