High voltage power supply for electron bombardment CMOS image sensor

Abstract

This invention discloses a high-voltage power supply for an electron bombardment CMOS image sensor, comprising a constant discontinuous mode flyback DC-AC circuit, a multi-stage CW positive and negative voltage multiplier rectifier circuit, a sampling circuit, and a voltage linear regulation circuit. Based on the strong boost capability of the flyback transformer in discontinuous mode under PWM control, and with an unbalanced CW positive and negative voltage multiplier rectifier circuit connected to the secondary side of the transformer, the forward turns ratio boost and reverse excitation boost characteristics of the transformer are simultaneously utilized. Combined with the PWM controller and peripheral circuit design, this ensures that the transformer operates only in discontinuous mode, significantly reducing the number of secondary turns and enabling the application of a smaller transformer. Sampling feedback from the low positive voltage output of the CW positive and negative voltage multiplier rectifier circuit allows the use of high-precision, low-resistance resistors. The operational amplifier design of the regulation circuit enables full-range adjustment of the output voltage under PWM control, improving linear regulation accuracy and realizing a small-power high-voltage power supply with a height of less than 5mm for miniaturized EBCMOS sensors.

Description

Technical Field

[0001] This invention belongs to the field of low-light night vision technology, and particularly relates to a high-voltage power supply for an electron-bombarded CMOS image sensor. Background Technology

[0002] With the development of low-light night vision technology, the electron impact CMOS image sensor (EBCMOS) combines the advantages of vacuum low-light image intensifier and solid-state low-light CMOS image sensor, achieving indicators such as low light, high gain, high signal-to-noise ratio, fast response speed, and small size, and has become one of the mainstream digital low-light night vision devices currently under development.

[0003] EBCMOS typically employs a board-to-board assembly structure. The front end comprises a vacuum ceramic-metal sealed assembly of the photocathode and CMOS image sensor. The middle and rear ends house the negative high-voltage power supply module, readout circuitry, power supply, and communication interfaces. These modules are interconnected via board-to-board connectors or flexible printed circuit boards. The negative high-voltage power supply powers the photocathode to achieve electron bombardment, with a very low power output, typically several to tens of milliwatts. To adapt to all-weather, day-and-night environments, the output of the negative high-voltage power supply must be linearly adjusted within a range of hundreds or even thousands of volts by an external regulating circuit to meet the electron bombardment gain settings under varying light intensities.

[0004] Current high-voltage power supplies for low-light night vision are mainly based on the self-resonant DC-DC principle, using high-turn-ratio transformers and multi-stage diode voltage multiplier circuits to achieve voltage boosting. The transformer winding is complex, requiring a large core window to wind multiple strands of wire, resulting in core heights mostly exceeding 5mm. The assembled high-voltage power supply is even taller. Furthermore, the wide-pitch, small-volume board-to-board connectors are difficult to select, forcing the high-voltage power supply to be placed at the last stage or connected via a flexible printed circuit board. This leads to a complex EBCMOS assembly structure, making it difficult to reduce the overall length and limiting miniaturization.

[0005] Current high-voltage power supply output voltage setting or regulation typically involves voltage division sampling via a high-voltage, high-resistance resistor connected in series at the high-voltage output terminal, or sampling through the transformer feedback winding. The large tolerance of high-resistance resistors leads to significant output voltage setting dispersion or linear fluctuations in regulation. Furthermore, high-turn-ratio transformers are not only bulky but also exhibit increased parasitic parameters such as leakage inductance and inter-turn capacitance, resulting in severe noise interference. The transformer feedback winding sampling method suffers from the same problem. Additionally, self-excited resonant DC-DC converters use feedback control of transistor conduction to adjust the transformer primary voltage. When the feedback voltage is lower than the transistor's on-state voltage drop, there is a zero output range, preventing full-range output adjustment and hindering EBCMOS power supply control. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings and provide a negative high voltage power supply for powering the photocathode of an electron bombardment CMOS image sensor (EBCMOS). The power supply is small in size, with a height of less than 5mm, and the output voltage can be controlled by an external adjustment circuit to achieve full-range adjustment from zero to full amplitude.

[0007] The design concept of this invention includes: First, based on the PWM control DC-DC principle, the transformer is designed to operate only in flyback discontinuous mode, utilizing its strong boost capability to enable the application of small-volume transformers with low turns ratios, reducing the size of the high-voltage power supply and meeting the miniaturization requirements of EBCMOS; Second, a low-amplitude, low-noise output voltage sampling circuit is designed, enabling the application of small-value, high-precision resistors to improve the accuracy of output voltage setting and linear adjustment; Finally, a linear control circuit is designed to enable controlled adjustment of the output voltage across the entire range from zero to full amplitude, meeting the all-weather, day-and-night operation requirements of EBCMOS.

[0008] Specifically, the technical solution of the present invention is as follows:

[0009] A high-voltage power supply for an electron-bombarded CMOS image sensor includes a constant discontinuous mode flyback DC-AC circuit, a multi-stage CW (Cockcroft-Walton) positive and negative voltage multiplier rectifier circuit, a sampling circuit, and a voltage linear regulation circuit; the constant discontinuous mode flyback DC-AC circuit consists of a transformer T1, a MOSFET Q1, a PWM controller U1, external resistors R6-R9, and a feedback compensation network. The multi-stage CW positive and negative voltage multiplier rectifier circuit includes a multi-stage negative voltage multiplier circuit and a two-stage positive voltage multiplier circuit. The multi-stage negative voltage multiplier circuit first consists of a capacitor C1, a diode D1, a capacitor C2, and a diode D2 forming a two-stage negative voltage multiplier circuit. Then, by repeatedly connecting the two-stage negative voltage multiplier circuit in series, an n-stage negative high voltage output is obtained. The two-stage positive voltage multiplier circuit consists of a capacitor Ca, a diode Da, a capacitor Cb, and a diode Db. The transformer operates constantly in flyback discontinuous mode (i.e., constant discontinuous mode) through a PWM controller and peripheral circuits. The secondary winding of the transformer is connected to the multi-stage CW positive and negative voltage multiplier rectifier circuit. The transformer transfers energy to the secondary winding when the MOSFET is turned on and off. The sampling circuit consists of a two-stage positive voltage multiplier circuit and resistors R1 and R2. The voltage linear regulation circuit consists of resistors R1-R5 and operational amplifier U2.

[0010] Furthermore, when the MOSFET is turned on, the input voltage V in After stepping up the voltage according to the transformer turns ratio, the positive secondary voltage V1 = (N S / N P V in The capacitors Ca and C2 are charged; when the MOSFET is turned off, the secondary N... SThe reverse excitation generates a high voltage V2 to charge capacitors Cb and C1; after several switching cycles, the negative high voltage V... N Establish a space between the right end of Cn and the ground, with a size equal to n(V1+V2) / 2.

[0011] Furthermore, the PWM controller is a low-operating-voltage current-type controller. Its current sampling signal amplitude is designed to be a large signal state close to the internal limit of the PWM controller, effectively limiting the PWM output pulse width and ensuring that the transformer can only operate in discontinuous mode. First, a transformer with a small primary inductance is selected, resulting in a steeper rise slope of the primary excitation current. Second, resistor R6 is designed with a large resistance value to increase the amplitude of the current sampling signal; resistor R7 is designed with a small resistance value to increase the DC bias voltage of the current sampling signal; finally, resistor R8 is designed with a large resistance value to reduce the switching frequency of the PWM controller and decrease the duty cycle of the PWM output. Additionally, resistor R9 is connected in series at the negative high-voltage output terminal, and V is then drawn out... N Even if V N When short-circuited, resistor R9 can also act as a fixed load, allowing the transformer to operate constantly in discontinuous mode.

[0012] Furthermore, the sampling circuit consists of two stages of positive voltage multiplier circuits and resistors R1 and R2. The positive voltage multiplier circuits produce a positive voltage output V with a relatively low amplitude. P Based on the voltage multiplier principle, the negative high voltage output V can be obtained. N =nV P / 2. Due to V P Since the amplitude is relatively low, low-voltage, low-resistance, high-precision resistors R1 and R2 can be used for voltage division sampling.

[0013] Furthermore, the voltage linear regulation circuit consists of resistors R1-R5 and an operational amplifier, forming an output voltage linear regulation circuit. Specifically, resistors R1 and R2 control the voltage V. P Voltage divider sampling is performed, and resistor R3 is used to sample the reference voltage V of the PWM controller. REF Sampling is performed, and the sampling results from both are connected to the non-inverting input of the operational amplifier; external control voltage V trim R4 is connected to the negative input of the operational amplifier, and R5 is the negative feedback proportional resistor. Appropriate values ​​are chosen for R1-R5 so that the output of the operational amplifier is only proportional to V. trim After feedback network compensation and PWM control of MOSFET switching, V is finally achieved. N =nV P / 2 = AV trim (A is a negative proportional constant). Since the PWM output duty cycle can be adjusted from 0 to 100%, therefore, in V... trim 0V-V can be achieved under control N Full-range linear adjustment.

[0014] The beneficial effects of this invention include:

[0015] This invention is based on the PWM-controlled discontinuous mode flyback DC-DC principle, and incorporates an unbalanced CW positive and negative voltage doubler rectifier circuit on the secondary side of the transformer. This allows the transformer's forward turns ratio boosting and reverse magnetization boosting characteristics to be utilized simultaneously. Combined with the PWM controller and peripheral circuit design, this ensures the transformer operates consistently in discontinuous mode, significantly reducing the required number of secondary turns. This allows for the use of conventional small transformers to achieve a low-power high-voltage power supply with a finished product height of less than 5mm, which is more conducive to EBCMOS miniaturization. The invention uses sampling feedback from the low positive voltage output of the CW positive and negative voltage doubler rectifier circuit, enabling the use of high-precision, low-resistance resistors. The operational amplifier design of the control circuit allows for full-range adjustment of the output voltage under PWM control, improving linear control accuracy and better meeting the power supply requirements of EBCMOS. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the main circuit of the high-voltage power supply of the present invention. Detailed Implementation

[0017] like Figure 1 As shown, the present invention provides a high-voltage power supply for an electron bombardment CMOS image sensor, the high-voltage power supply being composed of a constant discontinuous mode flyback DC-AC circuit, a multi-stage CW positive and negative voltage multiplier rectifier circuit, a sampling circuit, and a voltage linear regulation circuit.

[0018] The constant discontinuous mode flyback DC-AC circuit consists of a transformer T1, a MOSFET Q1, a PWM controller U1, external resistors R6-R9, and a feedback compensation network.

[0019] The multi-stage CW positive and negative voltage multiplier rectifier circuit includes a multi-stage negative voltage multiplier circuit and a two-stage positive voltage multiplier circuit. The multi-stage negative voltage multiplier circuit first consists of a capacitor C1, a diode D1, a capacitor C2, and a diode D2 forming a two-stage negative voltage multiplier circuit. Then, by repeatedly connecting the two-stage negative voltage multiplier circuit in series, a negative high voltage output after n-stage voltage multiplication is obtained. The two-stage positive voltage multiplier circuit consists of a capacitor Ca, a diode Da, a capacitor Cb, and a diode Db.

[0020] The sampling circuit consists of two positive voltage multiplier circuits and resistors R1 and R2.

[0021] The voltage linear regulation circuit consists of resistors R1-R5 and operational amplifier U2.

[0022] Pin 1 of the transformer T1 is connected to the input power supply V. inThe positive terminal of T1 is connected to the drain of the MOS transistor Q1. The third terminal of T1 is connected to one end of capacitors Ca and C1. The other ends of Ca and C1 are connected to the cathode of diode Da and the anode of diode D1, respectively. The fourth terminal of T1 is grounded.

[0023] Pins 1 and 2 of the PWM controller U1 are connected to a feedback compensation network (composed of a series and parallel combination of resistors and capacitors); pin 3 of U1 is connected to one end of resistors R6 and R7 and the source of MOSFET Q1, with the other end of R6 grounded and the other end of R7 connected to pin 8 of U1; pin 4 of U1 is connected to one end of resistor R8, with the other end of R8 grounded; pin 5 of U1 is grounded; pin 6 of U1 is connected to the gate of MOSFET Q1; pin 7 of U1 is connected to V... in The positive terminal of U1; pin 8 of U1 is connected to pin 3 of op-amp U2 and one end of resistor R3, and the other end of resistor R3 is connected to pin 2 of U2.

[0024] Pin 1 of the operational amplifier U2 is connected to one end of both resistors R4 and R5, and the other end of R4 is connected to an external control power supply V. trim The positive terminal of R5 is connected to the other end of U2, and the other end of R5 is connected to pin 4 of U2; pin 4 of U2 is connected to the feedback compensation network.

[0025] The cathode of diode D1 is grounded, and the anode of D1 is connected to both one end of capacitor C1 and the cathode of diode D2. The anode of D2 is connected to one end of C2. The two ends of D2 are connected to n similar combinations (C1, C2, D1, D2). Finally, a resistor R9 is connected to the anode of diode Dn, and a negative high voltage V is led out from the other end of resistor R9. N .

[0026] The anode of diode Da is grounded, the cathode of Da is connected to the anode of Db, and a positive high voltage V is drawn from the cathode of Db. P V P Connect one end of resistor R1, and connect the other end of R1 to both one end of R2 and pin 2 of U2. The other end of R2 is grounded.

[0027] Example

[0028] like Figure 1 As shown in the figure, as an example, the design and selection of each device parameter are as follows.

[0029] The input power supply V in =5V, the negative high voltage output V N Designed for -3kV.

[0030] The CW negative voltage multiplier stage is designed to have 20 stages, i.e., n=20, then the positive voltage output V P= +300V, the voltage across the voltage multiplier capacitor and diode is approximately 300V. Therefore, the capacitors Ca, Cb, and C1-C20, and the diodes Da, Db, and D1-D20, should be selected with a withstand voltage of 300V or higher.

[0031] The PWM controller is a general-purpose current-type controller powered by 5V, with an internal current sampling threshold of 1V and an internal reference voltage V. REF =5V.

[0032] The transformer T1 is selected with a turns ratio of 1:10, a primary inductance of 10uH, and is a small surface-mount transformer with a height of less than 2.5mm.

[0033] The resistor R8 is designed to be 120kΩ, with a switching frequency of approximately 24kHz, increasing the switching cycle and decreasing the duty cycle. The resistor R7 is designed to be 3kΩ, raising the primary current sampling signal level by approximately 0.7V, close to the current sampling threshold value inside the PWM controller. The resistor R6 is designed to be 1Ω, ensuring that the duty cycle corresponding to the primary current sampling signal reaching the 1V threshold is less than 10%. Through these designs, the transformer consistently operates in discontinuous mode. The resistor R9 is designed to be 1MΩ, ensuring that the transformer operates in discontinuous mode even when the output is short-circuited.

[0034] The MOSFET Q1 is a general-purpose NMOS with a drain-source voltage of 60V.

[0035] The operational amplifier U2 is a general-purpose rail-rail output operational amplifier. The resistors R1-R5 are designed with appropriate values ​​so that the output of the operational amplifier is proportional to the external control voltage V. trim The voltage across resistor R1 is close to V. P =+300V, select a resistor with a withstand voltage of 300V or higher.

[0036] The feedback compensation network is designed as a Type II feedback network.

Claims

1. A high-voltage power supply for an electron-bombardment CMOS image sensor, characterized in that, This includes a constant discontinuous mode flyback DC-AC circuit, a multi-stage CW positive and negative voltage doubler rectifier circuit, a sampling circuit, and a voltage linear regulation circuit. The constant discontinuous mode flyback DC-AC circuit includes a transformer, a MOSFET, a PWM controller, and PWM peripheral circuitry. The transformer operates continuously in flyback discontinuous mode through the PWM controller and peripheral circuitry. The secondary winding of the transformer is connected to a multi-stage CW positive and negative voltage doubler rectifier circuit. The transformer transfers energy to the secondary winding when the MOSFET is turned on and off. The multi-stage CW positive and negative voltage multiplier rectifier circuit includes a multi-stage negative voltage multiplier circuit and a two-stage positive voltage multiplier circuit. The multi-stage negative voltage multiplier circuit first consists of a capacitor C1, a diode D1, a capacitor C2, and a diode D2 forming a two-stage negative voltage multiplier circuit. Then, by repeatedly connecting the two-stage negative voltage multiplier circuit in series, an n-stage negative high voltage output is obtained. The two-stage positive voltage multiplier circuit consists of a capacitor Ca, a diode Da, a capacitor Cb, and a diode Db, and is used for output voltage sampling. The sampling circuit consists of two positive voltage multiplier circuits and resistors R1 and R2. The voltage linear regulation circuit consists of resistors R1-R5 and operational amplifier U2; The two-stage positive voltage multiplier circuit produces a low-amplitude, low-noise positive voltage output V. P =V1+V2; The resistors R1 and R2 are related to V P Voltage divider sampling is performed, and the resistor R3 is used to sample the reference voltage V of the PWM controller. REF The sampling results from both samples are connected together to the non-inverting input of the operational amplifier. External control voltage V trim The sample is connected to the negative phase input of the operational amplifier through resistor R4, and R5 is the negative feedback proportional resistor. The resistors R1-R5 are selected with appropriate values ​​so that the output of the operational amplifier is only proportional to V. trim Then, through feedback network compensation and PWM controller control of MOSFET switching, V is finally achieved. N =nV P / 2=AV trim A is a negative proportionality constant.

2. The high-voltage power supply according to claim 1, characterized in that: The transformer is a small surface-mounted transformer with a turns ratio Ns / Np of less than 10 and a primary inductance of less than 20uH, used to improve the rise slope of the primary excitation current.

3. The high-voltage power supply according to claim 1, characterized in that: The PWM controller is a low-operating-voltage current-type controller, and the current sampling signal is designed to be in a large-signal state.

4. The high-voltage power supply according to claim 1, characterized in that: The PWM peripheral circuit consists of resistors R6, R7, R8, R9 and a feedback network compensation network, which is composed of resistors and capacitors connected in series and parallel.

5. The high-voltage power supply according to claim 4, characterized in that: The resistor R6 samples the primary excitation current to obtain a current sampling signal. The resistor R7 raises the DC bias voltage of the current sampling signal so that the current sampling signal is approximately equal to the threshold value inside the PWM controller, which is used to limit the pulse width of the PWM output. The resistor R8 is used to set the switching frequency of the PWM controller to tens of kHz, which is used to increase the switching period and decrease the duty cycle. The resistor R9 is connected in series with the negative high voltage V. N At the output, even if V N When short-circuited, resistor R9 acts as a fixed load, limiting the maximum duty cycle of the PWM output.

6. The high-voltage power supply according to claim 1, characterized in that, When the MOSFET is turned on and off, the transformer transfers energy to the secondary side, specifically including: When MOSFET Q1 is turned on, the input voltage V in After stepping up the voltage according to the transformer turns ratio, the positive secondary voltage V1 = (N S / N P V in Charge capacitors Ca and C2; When MOSFET Q1 is turned off, the secondary winding is reverse-energized to produce a high voltage V2 to charge capacitors Cb and C1; after several switching cycles, the negative high voltage V... N Establish a space between the right end of Cn and the ground, with a size equal to n(V1+V2) / 2; The number n is even.

7. The high-voltage power supply according to any one of claims 1-6, characterized in that: The input voltage V of the high-voltage power supply in =5V, negative high voltage output voltage V N =-3kV.

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