Designing a low noise 45V-4A dual rail power supply using an enhanced capacitance multiplier would aim to deliver stable voltage while minimizing the ripple and noise that can affect sensitive electronic equipment. A dual rail power supply provides two voltage outputs, one positive and one negative, both referenced to a common ground.
Given the specifications, here is a simplified outline of how you might approach the design:
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Transformer Selection:
- Voltage Rating: Select a transformer with a secondary voltage high enough to account for rectifier dropout, regulator dropout, and the capacitance multiplier drop, but which will also provide an output of ±45V after regulation. Pay attention to the VA rating as well - it must handle at least 4A for each rail.
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Rectification:
- Use a full bridge rectifier suitable for at least 5A to handle the current without excessive heating and a voltage rating of at least 100V.
- The rectified voltage will have an approximate peak value of √2 times the RMS voltage of the transformer minus the diode drops.
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Filtering:
- Place a bulk capacitive filter (electrolytic capacitor) to smooth out the peaks of the full-wave rectified voltage.
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Enhanced Capacitance Multiplier:
- A capacitance multiplier is essentially a low pass filter that uses an active device (like a transistor) and a capacitor to create the effect of a much larger capacitor.
- Enhancement: To handle 4A, use a power transistor with a suitable heat sink. It must withstand high current and have a voltage rating above the maximum expected input.
- Regulation: The V_BE multiplier (a part of the capacitance multiplier) needs to be adjustable to fine-tune the output voltage to ±45V.
- Add small-value, high-frequency ceramic capacitors in parallel with the bulk capacitors on the input and output to reduce high-frequency noise.
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Final Regulation:
- Depending on the drop voltage across the capacitance multiplier, an additional linear regulator stage may be needed to precisely achieve the desired output.
- Each rail would need its own regulator, capable of handling the required voltage and current.
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Additional Filtering:
- On the output, provide additional LC or RC filters to further reduce any residual ripple or noise.
- Pay attention to the ESR (Equivalent Series Resistance) of the capacitors for minimizing noise.
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Protection:
- Include overcurrent and thermal protection, as regulatory circuits might overheat at high currents like 4A.
- A fuse or circuit breaker on the input and a thermal shutdown on the power transistor could be considered.
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Testing and Adjustment:
- After assembling the circuit, test the output under load and adjust the V_BE multiplier to fine-tune the output voltage to the desired levels.
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PCB and Thermal Design:
- Create a PCB layout that minimizes noise coupling. Power regulators and capacitance multipliers generate heat and require adequate heat sinking.
- Trace sizes should be substantial enough to handle 4A without excessive voltage drop or overheating.
In practice, specific component values and configurations would depend on further circuit analysis, simulations, and prototyping. Critical design considerations include thermal management (especially for the power transistor in the capacitance multiplier), the exact enhancement to the basic capacitance multiplier topology to handle the 4A current, the voltage ratings, and the desired noise performance (specifying how "low" the noise needs to be). Always prototype your design and test it under different load conditions to ensure stable operation before finalizing your design.