Miniaturization Design of Airborne Computer Power Supply

1 Overview

With the development of microelectronics technology, airborne computer hosts using large-scale and ultra-large-scale integrated circuits have become increasingly miniaturized, which has put forward requirements for further miniaturization of the volume and weight of their power supply components. However, the existing airborne computer power supplies have generally adopted switching regulated power supplies, and most of them are integrated modules, so their volume and weight have been reduced by 1/3 to 1/2 compared with discrete device power supplies. It is difficult to further reduce the volume and weight of the power supply. The following analyzes and discusses the ways to achieve power supply miniaturization.

2 Ways to Miniaturize Airborne Computer Power Supplies

Airborne computers are computers that can withstand harsh environments, and their power supply components must also meet the requirements of being able to withstand harsh environments, such as adapting to ambient temperatures of -55°C to +60°C and a wide input voltage range; they must also be resistant to vibration, impact, and electromagnetic interference, among other high reliability requirements. Therefore, when analyzing and exploring power miniaturization solutions, it is necessary to consider whether various electrical performance indicators can still be met when working in harsh environments.

2.1 Use DC/DC converter modules with higher power density

With the rise and rapid development of power electronics, DC/DC converter integrated power modules have been developed and put on the market in large quantities, and have been used more and more widely. However, the operating frequencies and conversion efficiencies of the module power supplies produced by various suppliers are different. Under the same output power, the volume and weight vary greatly, and the application environments are also different. Therefore, there are not many power modules that can be selected for designing power supply components that are small in size, light in weight, and can adapt to use in harsh environments. There are only a few foreign power modules that can be selected, such as VICOR and abbott in the United States, GA?A in France, and other power modules.

2.2 Give priority to power modules with multiple output voltages

Power modules with single-channel voltage output and multi-channel voltage output each have their own advantages and disadvantages. The former has only one output voltage, which is directly regulated, so the output voltage has high accuracy. The latter has several output voltages, but only the voltage output of the main circuit has high accuracy, and the rest are indirectly controlled, so the output voltage accuracy is relatively low. Since multiple voltages are to be realized by multiple single-output modules, they are larger than directly using multi-channel voltage output modules. In order to reduce the volume and weight, on the premise of meeting the technical requirements, power modules with multi-channel voltage output should be preferred, such as Abbott in the United States and GA-A modules in France, which have multi-channel outputs.

2.3 Use low voltage dropout linear integrated regulator as secondary voltage regulator

In the case of the widespread use of switch-type integrated voltage regulator modules, linear integrated voltage regulators (especially low-dropout linear integrated voltage regulators) are still widely used. For example, a three-terminal low-dropout linear integrated voltage regulator is used to obtain 3.3V from 5V through secondary voltage regulation, and a precise ±10V power supply is obtained from ±15V through secondary voltage regulation.

2.4 The necessary small number of peripheral discrete components should also use small and light surface mount components as much as possible.

The power supply components composed of integrated power modules still have a small number of discrete components, such as inductors for filtering, X capacitors and Y capacitors, and resistors for adjusting voltage, which are all of surface mount type.

2.5 When some non-standard output voltages required by power supply components cannot be obtained from a single power module, small power modules with standard voltage output can be used to connect them in series.

For example, a small ±15VGA?A power module can be used as a single output to obtain ±30V, and then connected in series to obtain ±60V.

2.6 When one supplier cannot meet the volume and weight requirements, power modules provided by multiple suppliers can be used for a combined design.

2.7 To reduce the volume and weight of the entire power supply, it is very necessary to attach the power module substrate to the inner wall of the chassis and use the metal shell to dissipate heat.

3 Miniaturization design of an airborne computer power supply

3.1 Technical requirements for power supply of an airborne computer

(1) Input voltage 28.5V (23~32VDC);

(2) Output voltage

Voltage type＋5V±15V±24V±60V＋12V

Output current 5A 0.8A 2A 0.1A 0.2A

Voltage stabilization accuracy ≤±1% ≤±1% ≤±1% ≤±2% ≤±2%

Ripple noise Vp?p≤50mV≤80mV≤100mV≤100mV≤100mV

(3) Working temperature: -55℃～+60℃;

(4) Overall dimensions: 178 mm × 105 mm × 20 mm;

(5) Weight ≤ 0.5 kg;

(6) Satisfy other airborne conditions.

3.2 Determine the design of power supply components according to technical requirements

Due to the characteristics of the power supply component, such as a wide variety of output voltages, a small given size, a large input voltage variation range, and a wide operating temperature range, a small, high-reliability military-grade power supply module must be selected.

(1) 5V (5A), ±15V (0.8A) The Abbott three-way output NB50TM/5/15/15-C power module produced in the United States is selected. The module outputs 5V (5A), ±15V (0.83A), has an operating temperature of -55℃ to +100℃, is packaged in a metal shell, and has an overall size of 76.2mm×50.8mm×9.7mm. Its performance meets the design requirements.

(2) ±24V (2A) Two VICOR power modules MI?J23?MX/S produced in the United States are selected. The module outputs 24V (3.1A), has an operating temperature of -55℃～+100℃, and an overall size of 57.9mm×45.7mm×12.7mm. Its performance meets the design requirements.

(3) ±60V (0.1A) and +12V (0.2A) use French-made GA?A power modules MGDB?04?J?F (/T) and MGDS?04?J?E (/T) respectively. The former outputs ±15V (130mA) or 30V (130mA), and the latter outputs +12V (330mA). The operating temperature is -55℃～+100℃, and the dimensions are 32mm×19.3mm×7mm. By connecting two of the former in series, a voltage of 60V can be obtained, and the performance meets the design requirements.

Figure 1 Power supply circuit diagram

3.3 Composition of the power supply circuit

The power supply circuit is shown in Figure 1.

3.4 Heat dissipation and discrete component processing

(1) Due to the different thicknesses of various power modules,

The module substrates are close to the case for heat dissipation, and appropriate structural treatment is made on the back wall of the computer case so that module substrates of different heights can be close to the back wall of the case, and thermal conductive glue or heat dissipation pads are applied in the middle to reduce contact thermal resistance.

(2) The filter capacitor uses CA45, CAK45 type chip solid state capacitor.

The maximum size of the electrolyte tantalum capacitor is 7.3mm×4.3mm×2.8mm, and the filter inductor adopts an inductor wound with a small magnetic core.

(3) TVS transient voltage absorption diode is used at the 28.5V input end

(1.5KE43A) and a small anti-interference filter.

4 Application Effects

All components in the power supply are assembled in a 178mm×105mm board, with a maximum component height of ≤13mm and a weight of ≤0.5kg. The power supply has been tested for various performances and high and low temperature experiments, and has been tested in conjunction with a computer. All of its technical performances have met the design requirements and the needs of the entire machine.