Low-EMI electron microscope high-voltage power supply

Abstract

The utility model relates to the technical field of high-voltage power supplies, and discloses a low-EMI electron microscope high-voltage power supply, which comprises a power circuit, an output voltage control circuit and a protection circuit, the power circuit comprises a direct-current power supply input, a self-excitation topology circuit, a boosting transformer and a voltage doubling rectifying circuit which are connected in sequence; the voltage control circuit comprises an output voltage sampling circuit, a voltage setting circuit and an error amplifier, the voltage sampling circuit outputs a voltage feedback signal and a voltage setting signal which serve as two input signals of the error amplifier, and after subtraction, a voltage control signal is output through a proportion-integration-differentiation link; the protection circuit is used for overcurrent and discharge protection. According to the utility model, the self-excitation topology circuit with closed-loop control is adopted, so that the voltage on the switch tube is in a sine-like oscillation state, no steep rising edge and falling edge exist, the EMI interference is very low, and the imaging quality of the electron microscope can be improved.

Description

Technical Field

[0001] The utility model relates to a high-voltage power supply, in particular to a low-EMI stable electric field generator, which is mainly used for accelerating electrons of an electron microscope. Background Art

[0002] Electron microscope is a precision instrument that is very sensitive to electromagnetic interference in the working environment, and electromagnetic interference will significantly affect the imaging effect. At present, the switch tubes of mainstream electron microscope power supplies all use external square wave excitation drive mode. The switch tubes work in a hard switching state, which will generate strong EMI interference signals. In order to shield the EMI signal, a large number of metal shielding covers are usually used for shielding, resulting in a complex structure. Utility Model Content

[0003] In order to solve the problems in the background technology, the utility model designs a low EMI high-voltage power supply for an electron microscope, which adopts a self-excited resonance method to allow the switch tube to work in the amplification area. There is no sudden change in voltage and current, and the generation of strong EMI interference signals is eliminated from the source.

[0004] The purpose of this utility model is achieved through the following technical solutions:

[0005] A low-EMI high-voltage power supply for an electron microscope comprises a power circuit, an output voltage control circuit and a protection circuit; the power circuit comprises a DC power supply input, a self-excited topology circuit, a step-up transformer and a voltage-doubling rectifier circuit, and the above circuits are connected in sequence; the voltage control circuit comprises an output voltage sampling circuit, a voltage setting circuit and an error amplifier, the voltage sampling circuit outputs a voltage feedback signal and a voltage setting signal as two input signals of the error amplifier, and after difference is made, a voltage control signal is output through a proportional-integral-differential link, so as to realize continuous adjustable output voltage; the protection circuit is used for overcurrent and discharge protection.

[0006] Furthermore, the DC power input in the power circuit is a +24V input, and a switching power supply with power factor correction is used.

[0007] Furthermore, the self-excited topology circuit uses a transistor as a switch tube, and achieves adjustable output voltage by closed-loop controlling the base signal of the transistor.

[0008] Furthermore, the step-up transformer adopts an RM10 magnetic core, and the number of turns of the primary winding, the excitation winding, and the secondary winding of the transformer is precisely calculated to obtain ideal power and voltage output.

[0009] Furthermore, the voltage doubler rectifier circuit adopts a 7-level voltage doubler, and the 2500V AC voltage output by the transformer is converted into a -30kV DC high voltage.

[0010] Furthermore, the voltage sampling circuit uses a sheet high-voltage resistor with an accuracy of 0.5%, which has a withstand voltage characteristic of up to 60kV and a high sampling accuracy.

[0011] Furthermore, the voltage setting circuit uses a high-precision, low-temperature drift voltage reference chip with an accuracy of 0.1% and 25ppm to provide a voltage setting reference, and obtains a high-precision and stable setting voltage through an adjustable potentiometer voltage divider.

[0012] Furthermore, the error amplifier adopts a PID loop design, so that the output voltage can follow the set voltage quickly and without error.

[0013] Furthermore, the protection circuit includes a PNP transistor and a comparator. When the power circuit is overcurrent or discharged, the PNP transistor turns off the control signal of the self-excited circuit and forcibly turns off the self-excited oscillation. When the overcurrent or discharge situation disappears, the self-excited oscillation is restarted, and this cycle is repeated to achieve overcurrent and discharge protection functions.

[0014] Furthermore, the output of the error amplifier is connected to the emitter of the protection circuit transistor, and is transmitted to the transistor base of the self-excited topology circuit via the protection circuit transistor collector, so as to control the conduction depth of the power circuit transistor.

[0015] Compared with the prior art, the utility model has the following advantages: The utility model adopts a self-excited topology circuit with closed-loop control, so that the voltage on the switch tube is in a quasi-sinusoidal oscillation state, without steep rising and falling edges, and the EMI interference is very low, which is beneficial to improving the imaging quality of the electron microscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a principle block diagram of the utility model.

[0017] Figure 2 This is a control circuit of the utility model.

[0018] Figure 3 This is a control protection circuit of the utility model.

[0019] Figure 4 This is the basic principle diagram of the self-excited topology of the utility model.

[0020] Figure 5 This is a voltage doubler rectifier circuit of the utility model. DETAILED DESCRIPTION

[0021] The utility model is further described in conjunction with the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, the low EMI high voltage power supply is composed of a power circuit and a control circuit to realize the product function.

[0023] like Figure 2 As shown in the figure, the control circuit includes an output voltage sampling circuit, a voltage setting circuit and a PID error amplifier circuit. The two resistors R1 and R2 are connected in series to divide the voltage, which serves as a voltage sampling circuit; the output voltage feedback signal and the voltage setting signal are used as two input signals of the PID. After the difference is made, a voltage control signal is output through the proportional-integral-differential link. Figure 3 The protection circuit in Figure 4 The base of medium power transistor TR1 controls the conduction depth of TR1 to achieve error-free regulation of the output voltage.

[0024] like Figure 3 As shown in the figure, the protection circuit includes a comparator and a P-type transistor TR2. The positive input terminal is connected to the current detection signal, and the negative input terminal is connected to the protection point setting voltage signal. When overcurrent or discharge occurs, the voltage signal at the positive input terminal is greater than the setting signal at the negative input terminal, and the comparator outputs a high level, which makes Figure 3 The transistor TR2 in the circuit is cut off. Figure 4 There is no control signal at the base of the power transistor, the oscillation stops, and there is no high voltage output.

[0025] like Figure 4 As shown, the 4th foot of the transformer is connected to the +24V DC power supply, the 3rd foot is connected to the collector of the power transistor TR1, and the emitter of the power transistor TR1 is grounded through the circuit sampling resistor to form a primary winding loop of the transformer; the 1st foot of the transformer is connected to the control signal from the PID, and the 2nd foot is connected to the base of the power transistor TR1, which together enhance the control signal; the output signal of the PID controls the conduction depth of the power transistor, which controls the oscillation intensity of the self-excited oscillation circuit, thereby controlling the output voltage of the transformer, and the output voltage of the transformer is used as Figure 5 The output voltage of the voltage doubler circuit, so the PID output signal can ultimately control the output voltage of the entire power supply.

[0026] Figure 5 It is a 7-level voltage doubler rectifier circuit. The left input terminal is connected to Figure 4 The output end of the transformer is the DC output voltage on the left, and the maximum output voltage is 14 times the input AC voltage amplitude.

[0027] Specific working process:

[0028] +24V power supply is connected, and the error amplifier detects whether the output voltage has reached the set voltage. If the output voltage is less than the set voltage, the PID output voltage increases, the conduction depth of the transistor in the self-excitation circuit is strengthened, the self-excitation oscillation amplitude is increased, and the output voltage increases until the set voltage is reached; on the contrary, if the output voltage is greater than the set voltage, the PID output voltage decreases, the conduction depth of the transistor in the self-excitation circuit is weakened, the self-excitation oscillation amplitude is reduced, and the output voltage decreases until it reaches the set voltage. During operation, if overcurrent or discharge occurs, the voltage of the current detection resistor increases and exceeds the protection set voltage. The comparator of the protection circuit outputs a high level, the PNP transistor is cut off, there is no signal input to the base of the power transistor, and the self-excitation oscillation stops. When the overcurrent or discharge disappears, the self-excitation oscillation restarts, and the cycle is repeated, thereby realizing the overcurrent and discharge protection functions.

[0029] In summary, the utility model achieves the expected purpose.

Claims

1. A low EMI high voltage power supply for an electron microscope, characterized in that: It includes a power circuit, an output voltage control circuit and a protection circuit; the power circuit includes a DC power supply input, a self-excited topology circuit, a step-up transformer and a voltage doubling rectifier circuit, and the above circuits are connected in sequence; the voltage control circuit includes an output voltage sampling circuit, a voltage setting circuit and an error amplifier, and the voltage sampling circuit outputs a voltage feedback signal and a voltage setting signal as two input signals of the error amplifier, and after difference is made, a voltage control signal is output through a proportional-integral-differential link to achieve continuous adjustable output voltage; the protection circuit is used for overcurrent and discharge protection.

2. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The DC power input in the power circuit is +24V input, and a switching power supply with power factor correction is adopted.

3. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The self-excited topology circuit uses a triode as a switch tube, and achieves adjustable output voltage by closed-loop controlling the base signal of the triode.

4. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The step-up transformer adopts RM10 magnetics.

5. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The voltage doubler rectifier circuit adopts 7-level voltage doubler, and the 2500V AC voltage output by the transformer is converted into a -30kV DC high voltage.

6. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The voltage sampling circuit uses a chip high-voltage resistor with an accuracy of 0.5%.

7. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The voltage setting circuit adopts a high-precision and low-temperature drift voltage reference chip with 0.1% accuracy and 25ppm to provide a voltage setting reference, and obtains a high-precision and stable setting voltage through an adjustable potentiometer voltage divider.

8. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The error amplifier adopts a PID loop design, so that the output voltage can follow the set voltage quickly and without error.

9. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The protection circuit includes a PNP transistor and a comparator. When the power circuit is overcurrent or discharged, the PNP transistor turns off the control signal of the self-excited circuit and forcibly turns off the self-excited oscillation. When the overcurrent or discharge situation disappears, the self-excited oscillation is restarted, and this cycle is repeated to achieve overcurrent and discharge protection functions.

10. A low EMI high voltage power supply for an electron microscope as claimed in claim 1, characterized in that: The output of the error amplifier is connected to the emitter of the protection circuit transistor, and is transmitted to the transistor base of the self-excited topology circuit through the collector of the protection circuit transistor, so as to control the conduction depth of the power circuit transistor.

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