Radar transmitter high voltage regulated power supply

1 Introduction

Modern radar transmitters have widely adopted grid-controlled power traveling wave tubes. Due to the improvement of the phase sensitivity of traveling wave tubes, in order to meet the radar system's requirements for the improvement factor, high requirements are placed on the stability and ripple of the high voltage of the tube body. In order to improve the efficiency of traveling wave tubes, the collector voltage reduction method is generally used, so its high voltage power supply consists of two groups, one is the tube body high voltage regulated power supply, and the other is the collector high voltage unregulated power supply. This article introduces the design ideas and design methods of a certain radar transmitter high voltage power supply.

2 Main technical requirements

1) Input voltage ~220V/400Hz (±5%).

2) Output tube high pressure

Voltage UA = 20 ~ 25kV, voltage stabilization, continuously adjustable;

Current Ia ≥ 15mA, pulse current Iap ≥ 1A;

Voltage stability Sv≤10-3 (input voltage ±5% change);

Load stability Si≤2.5×10-3 (load from no load to full load);

Ripple ≤10-4.

3) Output collection extremely high voltage

Voltage Uc = 15 ~ 18kV;

Current Ic ≥ 85mA, pulse current Icp ≥ 5.5A;

Ripple ≤5×10-3.

4) Ambient temperature

Working environment temperature (-15～55)℃;

Storage temperature (-45～75)℃;

Humidity: +40℃, (95±3)%.

5) Mean time between failures

MTBF≥1000h

3 Design ideas

1) Design purpose: high reliability, low failure rate, to ensure stable and reliable operation of the power supply in a high temperature, high humidity, high salt fog working environment, without discharge, corona, sparkover and other phenomena, and require small size, light weight, easy installation, commissioning and maintenance.

2) Technical indicators

——At present, the general high-voltage regulated power supply includes switching power supply, linear series power supply, linear parallel power supply and primary regulated power supply. Due to the requirements of high stability and ultra-low ripple, this design uses a linear circuit.

——Since the gate-controlled traveling wave tube uses collector voltage reduction, it requires a set of regulated power supply and a set of unregulated power supply. Generally, two sets of regulated power supply are designed. This method has the following defects for the traveling wave tube: two high-voltage transformers are required, and the rectifier bridge and filter capacitor need to withstand very high voltage (output DC voltage + tube voltage drop). Two sets of high-voltage power supply cannot meet

The requirement for synchronous power-on and power-off of the traveling wave tube can easily cause the voltage difference between the two sets of output voltages to be too large, causing the collector of the traveling wave tube to spark to the ground and cause a malfunction.

Therefore, we designed a dual-circuit high-voltage power supply with unique characteristics, which completely overcomes the above defects and is very suitable for the use of traveling wave tubes.

4. Introduction to the working principle of dual-circuit high-voltage power supply

4.1 Block Diagram

The principle block diagram is shown in Figure 1.

Figure 1 Principle block diagram

4.2 Principle Introduction

Input 400Hz/220V power supply, after the high-voltage transformer step-up conversion, the output two AC high voltages are sent to two groups of rectifiers and filters respectively, one of which is sent to the collector of the traveling wave tube as the collector voltage (Uc=15~18kV, Ic=85mA, without the need to make a special collector high voltage, which is the uniqueness of this circuit). In addition, the two groups of DC voltages after rectification and filtering are connected in series, and after the voltage is stabilized by the adjustment tube G, a highly stable DC voltage (UA=20~25kV, Ia≥15mA, adjustable voltage) is output to the synchronous pole of the traveling wave tube. A high-voltage silicon column D3 is connected between the cathode of the adjustment tube G and the series connection point of the two rectifiers to form an overvoltage protection circuit for the adjustment tube G. The highest voltage of the adjustment tube G is the output voltage of the rectifier V1 when it is unloaded. Therefore, the adjustment tube G can be selected with a very low withstand voltage. At the same time, the withstand voltage of the filter capacitors C1 and C2 is also reduced accordingly, thereby greatly reducing the volume and weight. In particular, sparking caused by high voltage difference due to inconsistent charging and discharging between two voltage groups is eliminated.

If the output voltage changes due to some factors, the sampling circuit samples and amplifies the change, sends it to the comparison amplifier for comparison with the reference voltage, and then sends it to the gate of the adjustment tube to change the control voltage on the gate, thereby changing the tube voltage drop on the adjustment tube, so that its output voltage remains unchanged, achieving the effect of voltage regulation.

In order to effectively eliminate arcing and sparking faults in high-voltage discharge, corona and high-humidity environments, the high-voltage transformer, high-voltage rectifier module and filter are combined into an independent oil-immersed high-voltage rectifier module, namely the "high-voltage assembly", and the casing is grounded. This greatly reduces the size and weight and makes installation easier. Compared with general traveling wave tube power supplies, the weight is much lighter and the size is reduced by more than half.

5. Selection of adjustment tube

5.1 Calculation of adjustment tube current IM

IM=IA+I0(1)

Where: IA is the traveling wave tube body current IA = 15mA;

I0 is the current in the sampling circuit and the bleeder resistor, I0=3mA.

Then IM=15+3=18mA

5.2 Calculation of the withstand voltage of the adjustment tube

1) Minimum pipe pressure drop value UAKmin

UAKmin=UA0+US(2)

Where: UA0 is the tube voltage drop when the adjustment tube is working normally, take UA0=2.5kV;

US is the voltage adjustment range of the regulated output, US=25-20=5kV.

Then UAKmin=2.5kV+5kV=7.5kV

2) Maximum pipe pressure drop

(1) Calculation of the maximum tube voltage drop value of traditional voltage stabilization circuit

When the grid voltage fluctuates by +5% and is unloaded (using capacitive filtering), the input voltage Uin of the adjustment tube is

Uin=(UAKmin+UA)×1.05×=(7.5+20)×1.05×=40.87kV

At this time, the tube voltage drop is UAK=Uin-UA=40.87-20=20.87kV

At this time, if the adjustment tube is cut off (output voltage UA=0), the tube voltage drop value is

UAKmax=Uin=40.87kV

Therefore, if two sets of power supplies are used to supply power independently, the withstand voltage of the adjustment tube must be >40.87kV, and such adjustment tubes are currently difficult to select. However, the dual-circuit high-voltage power supply greatly reduces the withstand voltage of the adjustment tube.

(2) Maximum voltage drop of the adjustment tube of the dual-circuit high-voltage power supply

Since the input voltage of the adjustment tube is provided by U1 and UC in series, UA=U1+UC

When the grid voltage fluctuates by +5% and the adjustment tube is cut off (output voltage UA=0), the maximum tube voltage drop UAKmax of the adjustment tube is

UAKmax=UA-UC=40.87kV-18.9kV=21.97kV

Then you can choose an adjustment tube with a withstand voltage greater than 21.97kV, which is easy to choose.

5.3 Calculation of the maximum power consumption of the adjustment tube PAM

PAM=UAK×IA(3)

Where: UAK is the tube voltage drop when the grid voltage fluctuates by +5% and the output voltage is 20kV,

UAK=(20+7.5)×1.05-20=8.88kV;

IA=18mA.

Then PAM=UAKIA=8.88×103×18×10-3=159.84W

According to the above calculations, a newly developed small metal ceramic triode T9730 from a Beijing institute was selected. This tube is small in size and light in weight, with stable and reliable performance, and fully meets the requirements of a dual-circuit voltage-stabilized power supply adjustment tube. Its main technical parameters are:

Maximum withstand voltage 30kV

Maximum current 300mA

Maximum power consumption 300W

6 Design of comparison amplifier circuit

The circuit uses triode voltage division sampling feedback, precision voltage regulator tube as reference, operational amplifier integrated circuit as comparison amplification circuit, and is structurally designed as a module that can be installed and debugged independently.

7 Dual-circuit high-voltage power supply test data

1) High pressure pipe

Voltage UA = 20 ~ 25kV voltage regulation, continuously adjustable;

Current IA = 15mA;

Voltage stability SV = 0.1%;

Current stability Si = 0.1%;

Ripple 2V.

2) Collecting extremely high voltage

Voltage UC = 18kV ± 2kV;

Current IC = 70mA;

Ripple voltage 13V.

8 Conclusion

The power supply has good performance in use, works stably and reliably, has strong ability to resist traveling wave tube sparking, and has good protection function. It is at the leading level among similar high-voltage power supplies.