Research on the Application of Module Power Supply in High Voltage Power Supply

Introduction

The radar transmitter has high requirements for the stability of its high voltage power supply. When designing high voltage power supplies, it is usually necessary to go through two or more stages of voltage regulation from the ordinary power supply system to meet output requirements. It is also necessary to consider issues such as power supply isolation, volume, heat dissipation, and reliability.

Module power supplies have significant advantages over discrete component power supplies in terms of flexibility, efficiency, and reliability. Using module power supplies can effectively design the first stage of voltage regulation for high voltage power supplies while meeting requirements for power supply isolation, volume, heat dissipation, and reliability, shortening the time spent on development or design changes, and saving labor and technical costs. This allows the design focus to be on the main circuit of the high voltage power supply, improving design efficiency.

1 Characteristics of Module Power Supplies

1.1 Advantages of Module Power Supplies

Module power supplies have the following advantages:

(1) A variety of types such as AC/DC, DC/DC, EMI modules, etc.

(2) Simple design. Power modules only require a small number of discrete components to obtain power. Module power supplies are generally equipped with standardized front ends, highly integrated power modules, and other components, greatly simplifying design applications.

(3) Shortened development cycle. Module power supplies generally have multiple input and output options. Users can also stack or cross-stack them to form modular power supplies, achieving multiple inputs and outputs, significantly reducing development time. Some module power supplies can be specially ordered if there are special needs.

(4) Flexible changes. If product design needs to change, it only requires switching or paralleling another suitable power module.

(5) Convenient heat dissipation. The module power supply casing has a structure that integrates a heat collector, heat sink, and casing. This achieves a conduction cooling method for the module power supply, bringing its temperature close to the minimum value, and the appearance of the module power supply is also quite aesthetic.

(6) High quality and reliability. Module power supplies are generally produced with full automation and equipped with high-tech production technology, resulting in stable and reliable quality.

1.2 Disadvantages of Module Power Supplies

Module power supplies have the following disadvantages:

(1) Generalized design of module power supplies. In certain special occasions with limited space and poor heat dissipation, there are few models of high power density module power supplies available, making selection difficult.

(2) Module power supplies are relatively expensive and occupy a certain amount of space and weight. Therefore, when designing, the power supply from module power supplies should meet usage requirements, and the number of modules should not be excessive to reduce space and weight costs.

1.3 Application Scope of Module Power Supplies in High Voltage Power Supplies

The main circuit of high voltage circuits consists of control circuits and high voltage generation circuits. Module power supplies can be used in parts such as AC power input, required low voltage DC control power supplies, filtering, or power factor compensation.

2 Requirements for Using Module Power Supplies in High Voltage Power Supplies

The high voltage power supply of the electron vacuum device radar transmitter requires special design and has high stability requirements. When designing high voltage power supplies, it is usually necessary to go through two or more stages of voltage regulation from the ordinary power supply system to meet output requirements. It is also necessary to consider issues such as power supply isolation, volume, heat dissipation, and reliability.

The range of module power supplies used in high voltage power supplies includes filtering power conversion circuits, control parts (low voltage), and the high voltage part generally does not use commercially available high voltage module power supplies but requires special design based on the parameters required by the transmitter. A block diagram of a certain type of high voltage power supply is shown in Figure 1.

2.1 Power Input and Control Circuit Analysis

The power input of the high voltage power supply consists of two parts: one part is AC power supply, usually generated by vehicle-mounted or airborne generators, typically at 400 Hz or 50 Hz, with voltage options around 115 V or 220 V. Small to medium power high voltage power supplies select single-phase power supply, while large power high voltage power supplies select three-phase power supply. The other part is low voltage DC power supply, mainly used for the control part of the high voltage power supply, such as ±5 V, ±15 V, ±27 V, etc., with generally small current and low power.

In actual systems, the high voltage power supply obtains power from the system, with AC power providing the power source and low voltage DC power providing control usage. For safety reasons, the system usually connects digital ground, analog ground, cable shielding layers, and chassis ground together, and some low voltage DC power return lines may even connect directly to the shielding layer or ground. The PWM control part of the high voltage power supply must compare with the high voltage feedback voltage, and the required low voltage DC power supply often needs to be powered separately, and for isolation reasons, its return line cannot be grounded. In this case, the system’s low voltage DC power supply cannot meet the requirements, and the high voltage power supply must use appropriate DC/DC module power supplies to generate the required isolated low voltage DC power supply.

2.2 Filtering and Power Conversion Circuit Analysis

The stability of the high voltage power supply has high requirements, and the output is often a multi-channel power supply, and usually, a single stage of voltage regulation cannot well meet the stability requirements of the high voltage power supply.

During power conversion, it is necessary to invert DC power into high-frequency AC power and send it to the high voltage transformer. After rectifying and filtering the AC input, a voltage regulation module power supply is used to provide DC/DC conversion, becoming the first stage of voltage regulation, and then inverting it into high-frequency AC power to send to the high voltage transformer for boosting and voltage regulation, which is the second stage of voltage regulation. Thus, going through two or more stages of voltage regulation from the ordinary power supply system to meet output requirements.

In addition, suitable AC/DC module power supplies, filtering, or power factor compensation modules can also be selected for the rectification and filtering of AC input.

2.3 Usage Requirements

The module power supplies used in the high voltage power supply of the transmitter must meet national military standards.

The module power supply’s physical structure must meet the respective requirements for installation, volume, heat dissipation, and weight of the high voltage power supply and be able to withstand the system’s strict environmental stress tests.

3 Application of Module Power Supplies

3.1 Output Voltage Adjustment

For module power supplies with TRIM or ADJ (adjustable output pin), the output voltage can be adjusted within a certain range using a resistor or potentiometer, generally within ±10%.

For TRIM output pins, connect the center of the potentiometer to TRIM, and for all +S, -S pins of the module, connect the other two ends to +S, -S respectively. If there are no +S, -S, connect the two ends to the corresponding positive and negative terminals of the main circuit (+S to +, -S to -UIN), and then adjust the potentiometer. The resistance value of the potentiometer is generally selected to be around 5 to 10 kΩ.

For ADJ output pins, there are input-side adjustment and output-side adjustment. The output-side adjustment is the same as the adjustment method for TRIM pins. The input-side adjustment can only increase the output voltage. At this time, one end of the potentiometer is connected to the center, and the other end is connected to the input ground.

3.2 Input Voltage Adjustment

Generally, module power supplies have built-in filters that can meet the requirements for general power supply applications. If a higher requirement power supply system is needed, an input filtering network should be added. LC or II type networks can be used, but it should be noted to choose smaller inductance and larger capacitance as much as possible.

To prevent transient high voltage damage to the module power supply, it is recommended that users connect a transient absorption diode at the input and use it with a fuse to ensure the module remains within a safe input voltage range. To reduce common mode noise, additional capacitance can be added, generally selecting high-frequency capacitors of several nF.

3.3 On/Off Circuit

The switching operation of the module power supply is conducted through the REM terminal. There are generally two control methods.

(1) When REM is connected to -UIN (reference ground), it is off, requiring UREF < 0.4 V. When REM is floating or connected to +UIN, the module operates, requiring UREM > 1 V.

(2) When REM is connected to UIN, it is off, requiring UREM < 0.4 V. When REM is connected to +UIN, the module operates, requiring UREM > 1 V. REM floating means it is off, known as “floating off” (-R).

If control needs to be isolated from the input, an optocoupler can be used to transmit the control signal.

3.4 Combination of Module Power Supplies

(1) Parallel Expansion. By paralleling the output terminals of the same module, the output capacity can be enhanced. However, the output voltage of the parallel modules must be adjusted to be relatively consistent to ensure current sharing and avoid unnecessary oscillations. For modules with larger output currents, lead resistance can be carefully designed to achieve current sharing. Modules paralleled in this way should not exceed two. Additionally, if one module fails, the entire system will not operate normally.

(2) Redundant Hot Backup. By paralleling the output terminals of the same module through diodes, the output capacity can be enhanced to improve the reliability of the power supply system. In principle, if paired with corresponding output alarm circuits, the modules should be placed on removable busbars, allowing for timely replacement of faulty modules. There is no limit to the number of modules paralleled using this method.

(3) Series Expansion. By connecting the output terminals of the same module in series, the output voltage can be multiplied, and the power will also increase accordingly. The series output terminals must be connected to diodes for protection.

4 Installation and Maintenance of Module Power Supplies

Due to the many categories, series, and specifications of module power supplies, their functional characteristics and physical properties vary. Therefore, there are also differences in installation, use, and maintenance.

Attention should be given to the following aspects.

(1) After opening the packaging, check whether the labels on each terminal match the instructions that come with it and whether they conform to the requirements set in the purchase contract. If there are discrepancies, contact the purchasing unit immediately to discuss a solution.

(2) In the first step of installation, the metal casing of the module power supply must be reliably grounded to ensure safety, but it should not mistakenly be connected to the neutral line.

(3) Before powering on after installation, double-check the connections on each terminal to ensure that input and output, AC and DC, single-phase and multi-phase, positive and negative poles, voltage values, and current values are all correct, eliminating the possibility of reverse or incorrect connections.

(4) For high power supplies, there are generally two or more “+” and “-” output terminals. In fact, this is for user wiring convenience; they are internally connected together and belong to one output electrode.

(5) Module power supplies should not be operated at full load for extended periods. The usage rate of linear power supplies should be controlled to within 60%; the usage rate of switching power supplies should be controlled to within 80%. Otherwise, it may cause premature failure of the module power supply.

(6) For some module power supplies, the manufacturer may have fixed resistors at the adjustable terminals (ADJ) upon leaving the factory. Users must provide corresponding value potentiometers to replace the fixed resistors. However, it should be noted that when the adjustable terminals are open, loading is strictly prohibited.

(7) To ensure sufficient heat dissipation, module power supplies should be installed in locations with good air circulation. For modules requiring heat sinks, the back panel must be evenly coated with thermal silicone grease, closely adhered to the heat sink, and fastened. Generally, it is required that linear power supplies operate at currents above 4 A or switching power supplies operate at currents above 7 A; forced air cooling should be added. Additionally, no other items are allowed to be placed on the module power supply casing.

(8) Module power supplies are generally suitable for resistive loads. If they need to be applied to capacitive or inductive loads, prior agreement should be made during ordering.

(9) The high voltage power supply of the transmitter usually does not use commercially available high voltage module power supplies but designs high voltage circuits specifically. If high voltage module power supplies are used, they must not be touched in the high voltage danger zone within 10 minutes after use or after power failure.

(10) Principles for selecting module power supplies: Generally, for higher power, switching power supplies should be chosen; for lower power, linear power supplies should be selected.

(11) Module power supplies are rarely damaged. When the high voltage power supply operates abnormally, such as not powering on, turn off the power supply and check whether the input and output terminals of the module power supply installed within the high voltage power supply are open or shorted. If these phenomena occur, it indicates that the module power supply is damaged, and it should be replaced. Module power supplies are usually sealed by the manufacturer and should not be forcibly disassembled.

5 Conclusion

In the design process of high voltage power supplies for radar transmitters, using module power supplies can effectively design the first stage of voltage regulation for high voltage power supplies while also considering power supply isolation, volume, heat dissipation, reliability, and other requirements. Moreover, it shortens the time spent on development or design changes, saving labor and technical costs. This allows the design focus to be on the main circuit of the high voltage power supply, improving design efficiency.

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