Magnetic isolation DC / DC converter

Abstract

A magnetic isolation DC / DC converter comprises an input circuit and at least two output circuits, the output circuits comprise a direct output circuit and a controllable output circuit, and the controllable output circuit comprises a voltage stabilizer used for controlling output voltage; the main control unit is used for acquiring electric energy from the input circuit and outputting a switching signal; the switching tube is used for switching to an on state or an off state according to the switching signal; the flyback transformer comprises a primary winding and a plurality of secondary windings corresponding to the output circuit, and the secondary windings are used for outputting the electric energy stored by the primary winding through the output circuit when the switching tube is switched to the cut-off state; and the feedback circuit is used for collecting the output voltage from the at least one direct output circuit and generating an error signal for controlling the switching signal according to the output voltage and the reference voltage, and the error signal is fed back to the main control unit. According to the utility model, the feedback circuit adopts an ADuM3190 isolation type error amplifier, and has excellent electrical isolation performance and temperature stability.

Description

Technical Field

[0001] The utility model relates to the technical field of DC / DC converters, and specifically relates to a magnetic isolation DC / DC converter. Background Art

[0002] DC-DC conversion is to convert a variable DC voltage into a stable DC voltage. Among them, PWM pulse width modulation is also called DC chopping. Isolated DC / DC is an important part of switching power supplies. Some DC / DC converters need to have the function of multiple outputs, that is, they can output multiple currents with the same or different voltages at the same time. The existing multi-output DC / DC converters have the following problems: 1. Poor feedback stability: Usually, one of the circuits is used as the feedback loop to obtain voltage information from the output circuit and feedback it to the main control chip. However, due to changes in external conditions such as temperature, the commonly used optocoupler feedback is easily affected, resulting in the deviation of the feedback voltage from the preset value, and ultimately causing unstable output; 2. Poor cross-regulation performance: The mutual influence between multiple outputs is difficult to effectively control, and the change of one load may cause the fluctuation of the output voltage of other circuits; 3. It is difficult to balance efficiency and stability: While ensuring the stability of multiple outputs, the overall efficiency is often sacrificed; 4. Insufficient anti-interference ability: In a complex electromagnetic environment, it is difficult for the existing technology to ensure the stability and reliability of each output.

[0003] Therefore, there is an urgent need for a DC / DC converter that can simultaneously meet the stability of multiple outputs, high efficiency, and strong anti-interference ability. Summary of the Utility Model

[0004] In order to solve the deficiencies in the prior art, the utility model provides a magnetic isolation DC / DC converter. By dividing the output circuit into a controllable output circuit with a voltage regulator and a common direct output circuit, it can provide stable current for electrical equipment through the controllable output circuit without being interfered by the feedback circuit.

[0005] To achieve the above purpose, the specific solution adopted by the utility model is as follows: an input circuit and at least two output circuits, the output circuit includes a direct output circuit and a controllable output circuit, and the controllable output circuit includes a voltage regulator for controlling the output voltage;

[0006] A main control unit for obtaining electrical energy from the input circuit and outputting a switching signal;

[0007] A switching tube for switching to a conducting state or a cutoff state according to the switching signal;

[0008] Flyback transformer, including a primary winding and multiple secondary windings corresponding to the output circuit, where the primary winding is used to obtain and store electrical energy from the input circuit when the switching transistor switches to the conducting state, and the secondary winding is used to output the electrical energy stored in the primary winding through the output circuit when the switching transistor switches to the cut-off state;

[0009] Feedback circuit, used to collect the output voltage from at least one direct output circuit, and generate an error signal for controlling the switching signal according to the output voltage and the reference voltage, and the error signal is fed back to the main control unit.

[0010] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The DC / DC converter further includes a power supply unit, the power supply unit includes an energy storage capacitor C20 connected to the input circuit and a resistor R10 for charging the energy storage capacitor C20, and when the energy storage capacitor C20 reaches the start threshold voltage, the main control unit powers on and starts.

[0011] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The input circuit includes a filter capacitor C1.

[0012] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The DC / DC converter further includes a frequency control unit, and the frequency control unit includes a frequency setting resistor R5 electrically connected to the main control unit.

[0013] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The DC / DC converter further includes an overcurrent and over-power protection unit, and the overcurrent and over-power protection unit includes a current detection resistor R12 electrically connected to the source electrode of the switching transistor and a front edge blanking filter circuit. The front edge blanking filter circuit includes a filter resistor R9 and a filter capacitor C15, and both the filter resistor R9 and the filter capacitor C15 are electrically connected to the main control unit.

[0014] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The DC / DC converter further includes a clamping circuit for protecting the switching transistor. The clamping circuit includes a resistor R2, a capacitor C6 and a diode D3. One end of the resistor R2 and one end of the capacitor C6 are both electrically connected to the input circuit, the other end of the resistor R2 and the other end of the capacitor C6 are both electrically connected to the negative electrode of the diode D3, and the positive electrode of the diode D3 is electrically connected to the drain electrode of the switching transistor.

[0015] As a further optimization of the above-mentioned magnetic isolation DC / DC converter: The feedback circuit includes an isolated error amplifier. The input end of the isolated error amplifier is electrically connected to all the output circuits. A resistor R19 and a capacitor C18 are connected in parallel at the output end of the isolated error amplifier, and both the resistor R19 and the capacitor C18 are electrically connected to the main control unit.

[0016] As a further optimization of the above magnetic isolation DC / DC converter: The feedback circuit includes voltage dividing resistors R20, R26 and a magnetic coupling voltage comparison sub-circuit, and the output end of the magnetic coupling voltage comparison sub-circuit is electrically connected to the input end of the isolated error amplifier.

[0017] As a further optimization of the above magnetic isolation DC / DC converter: The main control unit is set as a uc2843 main control chip.

[0018] Beneficial effects:

[0019] 1. By separating the controllable output circuit from the feedback circuit, the interference of the feedback to the stable output is effectively avoided, which is especially suitable for equipment with high requirements for power quality;

[0020] 2. Adopting a flyback topology and an optimized control strategy, while ensuring the stability of multiple outputs, a high overall efficiency is maintained; 3. Using an ADuM3190 isolated error amplifier and an optimized PCB design significantly improves the anti-interference ability of the system;

[0021] 4. The utility model has multiple protection measures and thermal management design, ensuring the reliable operation of the converter under various working conditions; 5. The multiple output design meets the requirements of modern electronic devices for various voltage demands and has a wide application prospect. Description of the Drawings

[0022] Figure 1 is the schematic diagram of the utility model;

[0023] Figure 2 is the PCB design diagram of the utility model. Specific Embodiments

[0024] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0025] As Figure 1 shown, a magnetic isolation DC / DC converter includes a main control unit, a switching transistor Q1, a flyback transformer, a feedback circuit, an input circuit and at least two output circuits.

[0026] An input circuit and at least two output circuits. The output circuits include a direct output circuit and a controllable output circuit. The controllable output circuit includes a voltage regulator for controlling the output voltage. The input circuit is connected to an external power supply to draw power from the external power supply. In this embodiment, the input voltage range of the input circuit is set to 40 - 300 VDC. To ensure the overall stability, the input circuit includes a filter capacitor C1 for eliminating the interference introduced by the input circuit. The capacitance value of the filter capacitor C1 needs to be calculated according to the overall output power of the converter. In this embodiment, the specification of the filter capacitor C1 is set to 0.47 uF / 630 V. A soft start circuit including a resistor R5 and a capacitor C21 is also provided. Increasing the value of C21 or R5 can extend the soft start time, while decreasing it will shorten the soft start time. When the power is first turned on, C21 is slowly charged through R5, thereby reducing the inrush current during startup and preventing the output voltage from overshooting.

[0027] The output circuits are connected to electrical equipment to supply power to the electrical equipment. The number of output circuits is determined according to actual requirements. In this embodiment, three output circuits are set. One of the output circuits is a controllable output circuit, which includes a 7815 three-terminal linear voltage regulator for outputting a 15V current. The other two output circuits are direct output circuits for outputting +24V and -24V currents. In the controllable output circuit, the 7815 three-terminal linear voltage regulator can generate a +15V output and provides a more stable output voltage, which is suitable for loads with high requirements for ripple. In addition, the three output circuits are implemented based on a multi-winding flyback transformer. The overall control and feedback of the converter are mainly based on one direct output circuit, while the other output circuits achieve basic regulation through the transformer winding ratio, thus achieving a balance among efficiency, cross-regulation, and output quality, and being suitable for application scenarios that require multiple voltages.

[0028] All three output circuits include an output filter sub-circuit composed of diodes, capacitors, and inductors, and the specific setting method is as Figure 1 shown. Each component of the output circuit, including resistors R15, capacitors C16, C21, etc., is used to set the gain and frequency compensation of the feedback control, as well as to detect and regulate the output voltage.

[0029] A main control unit for obtaining electrical energy from the input circuit and outputting a switching signal. In this embodiment, the main control unit is set as a uc2843 main control chip, which internally includes a fine-tunable oscillator, a latch pulse width modulator, a high-gain error amplifier, and a current comparator. The uc2843 chip is used for a wide temperature range, usually from -40°C to +85°C, and is suitable for various harsh environments to ensure reliable operation.

[0030] Considering that during the PWM pulse width modulation process, when the duty cycle exceeds 50%, sub-harmonic oscillation may occur. The harmonic oscillation will cause the output voltage of the output circuit to be unstable, thus affecting the overall performance of the converter. Therefore, the present utility model also provides a ramp compensation circuit. By injecting a ramp signal into the current detection signal transmitted to the uc2843 main control chip, that is, injecting a ramp signal into the error signal, sub-harmonic oscillation can be avoided. The core of the ramp compensation circuit is the high-frequency triode Q951. Q951 mainly plays a buffering and amplifying role to ensure that the ramp signal is effectively injected into the current detection signal. When the voltage of the COMP pin of the uc2843 main control chip changes, the base voltage of Q951 also changes, controlling its collector current and finally adjusting the magnitude of the ramp compensation signal. In addition, the ramp compensation circuit also includes a resistor R7, which is connected to the CT pin of the UC2843 and is used to adjust the amplitude of the ramp compensation.

[0031] The switching transistor Q1 is used to switch to the conducting state or the cut-off state according to the switching signal. The switching transistor Q1 uses a MOSFET transistor, and its gate is electrically connected to the OUT pin of the main control chip. In order to enable the switching transistor Q1 to turn off faster and reduce the switching loss, the gate drive of the switching transistor Q1 is optimized by setting the parallel-connected resistor R3 and diode D4, and a resistor R6 is connected to the gate of the switching transistor Q1. The resistor R6 is used to quickly release the gate charge when the switching transistor Q1 turns off, ensuring that it can turn off quickly and reducing the switching loss.

[0032] The flyback transformer includes a primary winding and a plurality of secondary windings corresponding to the output circuit. The primary winding is used to obtain and store electrical energy from the input circuit when the switching transistor Q1 switches to the conducting state, and the secondary winding is used to output the electrical energy stored in the primary winding through the output circuit when the switching transistor Q1 switches to the cut-off state.

[0033] A feedback circuit is used to collect the output voltage from at least one direct output circuit, and generate an error signal for controlling the switching signal based on the output voltage and the reference voltage. The error signal is fed back to the main control unit, enabling the main control unit to adjust the PWM duty cycle according to the feedback signal, thereby changing the switching time of the switching transistor Q1, achieving the effect of regulating the power transfer process of the primary winding, and ensuring the stability of the output voltage of the output circuit. The feedback circuit includes an isolated error amplifier, voltage-dividing resistors R20, R26, and a magnetic-coupled voltage comparison sub-circuit. The input terminal of the isolated error amplifier is electrically connected to all output circuits. A resistor R19 and a capacitor C18 are connected in parallel to the output terminal of the isolated error amplifier, and both the resistor R19 and the capacitor C18 are electrically connected to the main control unit. The voltage-dividing resistor R20 is used to draw power from two 24V output circuits by voltage division. The output terminal of the magnetic-coupled voltage comparison sub-circuit is electrically connected to the input terminal of the isolated error amplifier. In the present utility model, the model of the isolated error amplifier is selected as ADuM3190. ADuM3190 is a magnetic-coupled isolation device with excellent electrical isolation performance, which can effectively resist electrical noise and transient interference, improve the anti-interference ability of the converter. Its transmission function does not change with the life cycle and remains stable within a wide temperature range of -40°C to +125°C. It has higher speed and better linearity. Moreover, ADuM3190 is built with a broadband operational amplifier, which can provide accurate error amplification function, making the regulation of the output voltage of the output circuit more accurate.

[0034] In addition, besides the above-mentioned parts, the DC / DC converter further includes a power supply unit, a frequency control unit, an over-current and over-power protection unit, and a clamping circuit.

[0035] The power supply unit is used to supply power to the main control unit. The power supply unit includes an energy storage capacitor C20 connected to the input circuit and a resistor R10 for charging the energy storage capacitor C20. When the energy storage capacitor C20 reaches the startup threshold voltage, the main control unit powers on and starts.

[0036] The frequency control unit. The frequency control unit includes a frequency setting resistor R5 electrically connected to the main control unit. The frequency setting resistor R5 and the capacitor C10 form an RC frequency setting circuit for determining the frequency of the main control unit and are connected to the CT pin of the uc2843 chip.

[0037] Overcurrent and over-power protection unit. The overcurrent and over-power protection unit includes a current detection resistor R12 electrically connected to the source electrode of the switching transistor Q1 and a front-edge blanking and filtering circuit. The front-edge blanking and filtering circuit includes a filtering resistor R9 and a filtering capacitor C15, and both the filtering resistor R9 and the filtering capacitor C15 are electrically connected to the main control unit. Specifically, they are electrically connected to the Isen pin of the uc2843 chip. The filtering resistor R9 and the filtering capacitor C15 form an RC filter to eliminate high-frequency noise and glitch signals during the switching instant, ensuring the accuracy of the current detection signal and preventing false triggering.

[0038] The multi-output DC / DC converter of the present utility model divides the output circuit into a controllable output circuit including a voltage regulator and an ordinary direct output circuit. The feedback circuit obtains voltage information from the direct output circuit without affecting the stability of the controllable output circuit. For electrical equipment that requires stable power supply, it can be connected to the controllable output circuit to avoid affecting the stability of the electrical equipment during the power-taking process of the feedback circuit and ensure that the electrical equipment can operate stably.

[0039] The present utility model adopts multiple protection measures, including current protection, noise suppression, and RCD voltage clamping, ensuring that the converter can operate safely and reliably. When the DC / DC converter of the present utility model is applied in a power supply system, it can significantly improve the performance, efficiency, and reliability of the power supply system, meeting the high requirements of modern electronic equipment for the quality and stability of the power supply system.

[0040] Clamping circuit for protecting the switching transistor Q1. The clamping circuit includes a resistor R2, a capacitor C6, and a diode D3. One end of the resistor R2 and one end of the capacitor C6 are both electrically connected to the input circuit. The other end of the resistor R2 and the other end of the capacitor C6 are both electrically connected to the negative electrode of the diode D3. The positive electrode of the diode D3 is electrically connected to the drain electrode of the switching transistor Q1. When the switching transistor Q1 is in the cut-off state, due to the existence of leakage inductance in the flyback transformer, a spike voltage is likely to be generated, which may damage the switching transistor Q1. By setting the clamping circuit, the energy of the spike voltage can be consumed on the capacitor C6, thus avoiding the generation of instantaneous overvoltage on the switching transistor Q1 and realizing the protection of the switching transistor Q1.

[0041] To further improve the reliability of the present utility model, a temperature detection voltage division network including an NTC and an R30 is also provided. As the temperature rises, the resistance value of the NTC decreases, and the voltage at the voltage division point rises. R60 and R40 form a fixed reference voltage division network. C33 is connected between the NTC and the ground to filter out high-frequency noise. R33 is connected between the voltage division point of the NTC and R30 and the positive input of the comparator to provide slight positive feedback, which helps to generate a hysteresis effect. As the temperature rises, the resistance value of the NTC decreases, and the voltage at the connection point of the NTC and R30 will rise. When this voltage exceeds the voltage at the voltage division point of R60 and R40, the output of the LM393 will change. This change is transmitted to the main control IC through the COMP signal to trigger over-temperature protection. C33 improves the stability of temperature detection and reduces noise interference. R33 helps to prevent frequent switching near the critical point and can provide more reliable over-temperature protection.

[0042] As Figure 2 shown, it should also be noted that in the PCB, large-current traces are realized in the form of copper cladding, and at the ends of the large-current path segments, so as to fully reduce the parasitic inductance and parasitic resistance, thereby reducing the loss and voltage drop. In addition, the thickness of the copper cladding is larger than that of other areas, so that it can carry a larger current and reduce heat accumulation.

[0043] The ground terminal of the isolated error amplifier is separated from the ground terminal of the large-current line to avoid the influence of the large-current line on the output voltage fluctuation. At the same time, its feedback lines are arranged in parallel to maintain the integrity of the signal. Moreover, the traces of the feedback circuit are far away from the flyback transformer and the switching transistor Q1 to avoid mutual interference. The ground layers of the primary side and the secondary side of the ADuM3190 and the flyback transformer are separated, and are only connected through coupling capacitors or common-mode inductors at necessary positions to reduce ground loop interference. Similarly, the filter capacitors are placed as close as possible to the power pins of the relevant devices to reduce power supply noise. The R9 and C15 of the front-edge blanking circuit and other frequency compensation components should be as close as possible to the relevant pins of the uc2843 to reduce interference.

[0044] Slotting is performed under the flyback transformer, and heat dissipation vias and heat dissipation pads are provided on the packages of the switching transistors Q1, Q951, all the diodes, and the main control unit to achieve sufficient heat dissipation, ensure the overall stability of the converter, and extend the service life.

[0045] The entire PCB uses a multi-layer design. Among them, the power layer and the ground layer can reduce the power impedance and the signal loop path, improve the stability of the overall circuit, and ensure the integrity of the ground layer to avoid too long signal return paths, so as to reduce EMI problems.

[0046] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present utility model. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present utility model. Therefore, the present utility model will not be limited to these embodiments shown herein, but rather should be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A magnetic isolation DC / DC converter, characterized in that, Comprising: An input circuit and at least two output circuits, the output circuits including a direct output circuit and a controllable output circuit, wherein the controllable output circuit includes a voltage regulator for controlling the output voltage; A main control unit for obtaining electric energy from the input circuit and outputting a switching signal; A switching transistor for switching to a conducting state or a cutoff state according to the switching signal; A flyback transformer including a primary winding and a plurality of secondary windings corresponding to the output circuits, wherein the primary winding is used to obtain and store electric energy from the input circuit when the switching transistor switches to the conducting state, and the secondary windings are used to output the electric energy stored in the primary winding through the output circuits when the switching transistor switches to the cutoff state; A feedback circuit for collecting the output voltage from at least one direct output circuit and generating an error signal for controlling the switching signal according to the output voltage and a reference voltage, the error signal being fed back to the main control unit.

2. The magnetic isolation DC / DC converter according to claim 1, characterized in that, The DC / DC converter further includes a power supply unit, the power supply unit including an energy storage capacitor C20 connected to the input circuit and a resistor R10 for charging the energy storage capacitor C20, and the main control unit powers on and starts when the energy storage capacitor C20 reaches the startup threshold voltage.

3. A magnetic isolation DC / DC converter according to claim 1, characterized in that, The input circuit includes a filter capacitor C1.

4. A magnetic isolation DC / DC converter according to claim 1, characterized in that, The DC / DC converter further includes a frequency control unit, the frequency control unit including a frequency setting resistor R5 electrically connected to the main control unit.

5. A magnetic isolation DC / DC converter according to claim 1, wherein, The DC / DC converter further includes an overcurrent and over-power protection unit, the overcurrent and over-power protection unit including a current detection resistor R12 electrically connected to the source electrode of the switching transistor and a front edge blanking filter circuit, the front edge blanking filter circuit including a filter resistor R9 and a filter capacitor C15, and both the filter resistor R9 and the filter capacitor C15 are electrically connected to the main control unit.

6. The magnetic isolation DC / DC converter according to claim 1, wherein, The DC / DC converter further includes a clamping circuit for protecting the switching transistor, the clamping circuit including a resistor R2, a capacitor C6 and a diode D3, wherein one end of the resistor R2 and one end of the capacitor C6 are both electrically connected to the input circuit, the other end of the resistor R2 and the other end of the capacitor C6 are both electrically connected to the negative electrode of the diode D3, and the positive electrode of the diode D3 is electrically connected to the drain electrode of the switching transistor.

7. A magnetic isolation DC / DC converter according to claim 1, characterized in that, The feedback circuit includes an isolated error amplifier, the input end of the isolated error amplifier is electrically connected to all the output circuits, a resistor R19 and a capacitor C18 are connected in parallel at the output end of the isolated error amplifier, and both the resistor R19 and the capacitor C18 are electrically connected to the main control unit.

8. A magnetic isolation DC / DC converter as claimed in claim 7, characterized in that, The feedback circuit includes voltage dividing resistors R20, R26 and a magnetic coupling voltage comparison sub-circuit, the output end of the magnetic coupling voltage comparison sub-circuit is electrically connected to the input end of the isolated error amplifier.

9. A magnetic isolation DC / DC converter according to claim 1, wherein The main control unit is set as a uc2843 main control chip.

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