Abstract: Elaborated one kind of miniaturized high-voltage power supply, as soon as it changes traditional high pressure, the low pressure combined type is the integrated type, thus causes the volume, the weight greatly to reduce. Simultaneously had pointed out the switching power supply technology the question which and the solution exists in the high-pressured low power power source application. In developed and in the experiment process has applied the PSPICE emulation technique, gave actual and the simulation profile.
Key word: Miniaturization high tension transformer high-voltage power supply simulation
Introduction
The high-voltage power supply widely was already applied? Check-out facilities and so on medicine, industry lossless crack detection, station, customs examination, also widely applies in such as military fields and so on radar transmitter, electronic aeronautical chart monitor. The traditional high-voltage power supply volume is big, is unwieldy, serious influence supplementary equipment’s development. The present high-voltage power supply uses the switching power supply form, reduced the volume weight greatly, increased the power, raised the efficiency. Specially the high-pressured low power switching power supply, nearly is the switching power supply structure. This article discusses the high-pressured low power switching power supply, is the X-ray television perspective systems assembly design. This kind of system is to the primitive X-ray equipment’s improvement, it increases a named image intensifier’s equipment. This kind of equipment uses the electrode to carry on the acceleration and the focusing to the electron, thus needs with it necessary low power high-voltage power supply.
1 plan choice
The low power high-voltage power supply most commonly used example is television’s anode high pressure producer, it several dozens volt direct-current power supplies, through power transformation and high tension transformer pressure-rise, the rectification filter, become the high-pressured output again; Another application example is the anoin generator, often uses the thyristor accent to press the way. The above two kind of accents press the way to need an independent adjustable accessory power supply, namely high-pressured, low pressure combination way. This has then enlarged power source’s volume and the complex degree. Adds it, as a result of the circuit structure form’s difference, their output voltage scope’s adjustment is very limited, when needs the wide range adjustment, can only through the change power line voltage realize. But X-ray intensifier’s main road voltage regulation scope near 10kV, the above electric circuit form is very difficult to satisfy the request. This article uses half bridge resonance type switching power supply, has solved the above problem successfully.
2 technical specifications
Input voltage 220 (1±10%) V, (50±0.5) Hz; Or wide scope input voltage 180~250V.
Output voltage/electric current
Anode () voltage/electric current
Nominal value 25kV/1mA,
Voltage range 23kV~ 32kV;
Nominal value 7.35kV/200μA,
Voltage range 6.0kV~ 7.8kV;
Nominal value 0.985kV/200μA;
Voltage range 0.8kV~ 1.1kV;
Negative pole (negative) voltage/electric current
Nominal value - 0.75kV/500μA;
Voltage range - 0.5kV~-1kV.
Above 4 group voltage gearing output.
Stability 1%.
Operating temperature scope 0℃~ 40℃.
Storage temperature range - 40℃~ 55℃.
External dimensions 160mm×135mm×43mm.
Image intensifier’s electrode when processing the inevitable existence has the burr, under high voltage point discharge puncture flame. Must burn down the burr, needs to have the big electric current. Thus, on the one hand requests the power source output to design wants big, on the other hand should have the consummation protective measures.
3 system diagrams and principles of work
25kV miniaturization high-voltage power supply’s system diagram as shown in Figure 1.
The input city electricity after purifying the filter the rectification becomes about 300V the DC voltage to add to half bridge electric circuit’s MOS tube. The control circuit is composed of the most commonly used SG3525 chip. The control circuit through the high-pressured part feedback winding examination output voltage’s change quantity, produces the excitation pulse driver power MOS field effect tube, realizes the constant voltage output.
4 technical difficulties and solution
4.1 volumes and insulation
This kind of power source is specially the X-ray intensifier necessary, it is installed in the X-ray intensifier foundation next narrow and small space, thus the request volume is small. The volume reduces and circuit form the choice, electric circuit’s performance and the insulation, radiates and so on questions to have the direct relation. This electric circuit parts and the high-pressured part and so on power transformation, control circuit separates the shield laying aside, and chooses the high strength isolation medium packing high pressure part, has solved this problem well.
4.2 high frequency high tension transformers
The high frequency high tension transformer is high-voltage power supply’s core part. In the low pressure (power) in the transformer, may not consider the profile the distortion and the working band question, thus may neglect distributed capacity’s influence. In high frequency high tension transformer, because the number of windings increase, specially the secondary number of windings increase, when the transformer operating frequency is quite high and the voltage rate of change is quite big, must consider the distributed capacity and the leakage inductance question. By now, transformer model as shown in Figure 2. L1 is the leakage inductance, Cp and Cs respectively is primary and the secondary distributed capacity. Transformer leakage inductance L1 and the secondary distributed capacity constituted the series resonance circuit. When the transformer secondary opening or the load are light the transformer may regard as the inductance, thus constitutes the antiresonance circuit with secondary distributed capacity Cs, its equivalent circuit as shown in Figure 3. When has the resonance, the electric capacity both sides’ voltage will be higher than the working voltage, i.e. the transformer internal voltage will be higher than the output voltage. This has increased imperceptibly to transformer’s pressure resistance request. Therefore in the transformer circles in the system process, must reduce the distributed capacity and the leakage inductance as far as possible. Supposition each electric capacity is equal, the winding altogether has m, then distributed capacity Cs=C (C is secondary natural capacity, N2 is secondary number of windings). When the secondary number of windings are certain, secondary equivalent to primary distributed capacity and secondary layer related, the layer are more distributed capacity to be smaller. Each on number of windings are less, the distributed capacity is smaller. In order to reduce the distributed capacity, adopts the partition grouping to circle the system way, and increases the layer, reduces each number of windings. The transformer uses the U-shaped ferrites magnetic core, it circles system hint as shown in Figure 4.
The practice proved that the partition grouping circled the facture also well to solve high tension transformer’s insulation problem.
4.3 input voltage scope modulation
The work under the high frequency high-pressured condition’s low power power source, the input voltage scope’s adjustment can have the difficulty. Not only the relative regulation is very bad, moreover when the input voltage surpasses certain value, the power source reliefs, or the output voltage is unstable. The reason is the high-pressured low power power source’s dutyfactor is very small, time the work breakover pulse width is very narrow (assumes narrow pulse active status). When the input voltage elevates, the output energy is invariable, the pulse width stricts, scope lengthen. The input voltage elevates to certain limit, the control circuit assumes the out of control condition, is unable to realize the effective closed-loop control, causes the entire electric circuit closure. In order to solve this problem, undergoes the analytical investigation, has designed an input voltage regulation circuit, as shown in Figure 5.
It in fact is an input voltage pre-voltage-stabilizer circuit, the input voltage passes through it, becomes the basic stable voltage, adds to the main circuit again (switching circuit) on.
After the debugging, the experiment and the long-term installing equipment application, have proven this electric circuit’s stability and the unreliability. Table 1 is establishes the input voltage regulation circuit with has not established when the measured data. For simplicity, here only gives outputs the main circuit (25kV) the parameter. Sees obviously, after adding this electric circuit, the input voltage relative regulation greatly enhances, the input voltage regulation band also increases to 250V.
Table 1 input voltage change to output voltage influence
|
Input voltage /V |
Has input voltage adjustment output voltage /kV |
Non-input voltage adjustment output voltage /kV |
|
180 |
26.2 |
22 |
|
198 |
26.4 |
26.1 |
|
220 |
27 |
28.5 |
|
242 |
27.5 |
Reliefing |
|
250 |
27.7 |
Reliefing |
Because on time electricity, the input end instantaneous surge current is very big, causes the harm to the input voltage regulation circuit. Therefore, but also has designed the input block electric circuit specially.
Moreover, high-voltage power supply transformer’s changing is bigger than n, the transformer feeds back to the primary rate of change is small, the question which brings is secondarily the constant voltage effect is not ideal. Thus, but also has designed the output voltage pre-voltage-stabilizer circuit. Because the length is limited, actual electric circuit omitting.
5 switching circuit’s simulation experiment
Switch level electric circuit schematic diagram as shown in Figure 6. Here switch level’s load is the high frequency high tension transformer, its input characteristic and the load characteristic concerns. In high-pressured low power application, because the output current is small, the load resistance is big, the secondary rectification diode’s breakover angle is very small. In order to be advantageous for the establishment simulation model. May neglect the load resistance the influence.
Because has applied the emulation technique, simplified the experiment process greatly, reduced the design cycle. The electric circuit divides into the underloading with the PSPICE simulated program to Figure 6 10μA and the heavy load 1mA two kind of situations carries on the simulation, finally sees Figure 7(a) and Figure 8(a). Will carry on later in the electric circuit experiment, the actual current waveform will see Figure 7(b) and Figure 8(b) tallies basically with the simulation profile. Moreover, may also see time the underloading from the simulation profile the surge current peak value to be big, with heavy load when is nearly equal. The transformer no-load loss increase, cause the transformer to give off heat, this is the question which needs to further solve.
6 conclusions
After the small batch production and several year installing equipment use, proved that this power source has achieved the design requirements, the stable property, reliably, may substitute (the Thomsen power source which the same type product e.g. Japanese some company produces).
In the X-ray intensifier production working procedure, must dispose a big power the high pressure (output voltage to reach as high as 30kV) the power source, fifty-fifty the end product carries on the aging, hits the burr. Because this power source performance has satisfied the above request, may use for to substitute this big power power source, both has saved the equipment, and reduced the production processing cycle.
