The core element of any electronic device is the power supply. Any instability or malfunction of the power supply causes the device to malfunction or demonstrate weird behavior. In some sensitive applications, we need a dual voltage-rail power supply to prepare a high current and low noise voltage at the output. In this article, I introduced a low-noise AC-to-DC power supply that can handle up to 4 A continuously and accept input voltages up to 35 V-AC.
To design this power supply, I decided to use an enhanced capacitance multiplier circuit. I paid high attention to good grounding, assigned the top layer of the PCB to the ground, and drew power planes instead of tracks to carry high currents. As a result, I could not detect any noise or ripple at the output even at the maximum output current!
I tested the board for voltage drop, current delivery, and output noise. I used Siglent SDL1020X-E DC load and Siglent SDS2102X Plus oscilloscope to perform all tests. I’m confident that this design satisfies your needs in many applications.
Specifications
- Input voltage (max): 35 V-AC
- Output current: 4 A continuous
- Output noise/ripple: very low
- Output voltage: 45 V-DC (maximum safe, under no load)
Circuit analysis
Figure 1 shows the schematic diagram of the circuit. The core of the design is an enhanced capacitance multiplier circuit.
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| Figure 1. | Schematic diagram of the low noise 45 V-4 A dual rail power supply. |
AC-IN is a KF129 terminal connector to connect your center-tapped AC transformer to the circuit. BR is a D15XB60 high-current bridge rectifier that can work up to 3 A-4 A without any heatsink. C1…C4 are input capacitors for preliminary ripple reduction because the ripple rate at the input is extremely high. Each pair of these capacitors is placed in parallel to reduce the equivalent ESR (two ESR resistors in parallel). The rest of the circuit is the capacitance multiplier circuit. T1, T3, and T2, T4 create a Darlington transistor to multiply the equivalent capacitance even more. In my experiments, this kind of arrangement handles better performance than using a single Darlington transistor.
D2 and D3 protect the T3 and T4 transistors from reverse currents. R7 and R8 are a few milliamps dummy loads to stabilize the output voltage.
PCB layout
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| Figure 2. | PCB layout of the low noise 45 V-4 A dual rail power supply. |
Figure 2 shows the PCB layout of the design. It’s a two-layer PCB board and all component packages are through-hole. This makes it easy even for beginners to build this circuit. Table 1 shows the bill of materials.
| Table 1. | Bill of materials | ||||||||||||||||||||||||||||||||||||||||||
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As it’s clear in the picture, I assigned the top layer just to the ground and it’s a solid ground plane. In addition to the routing techniques for the bottom layer, this PCB is expected to demonstrate low noise figures.
Assembly and test
Figure 3 shows the assembled PCB board.
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| Figure 3. | Assembled PCB board of the low noise 45 V-4 A dual rail power supply. |
I run several tests to verify the performance of the circuit. Figure 4 shows the output noise of the power supply under no load, and Figure 5 shows the output noise under a 4 A load. Tests have been performed using the Siglent SDS2102X Plus oscilloscope. My oscilloscope could not pick up any noise at the output indeed.
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| Figure 4. | Output noise of the Low Noise 45 V-4 A dual rail power supply (no load). |
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| Figure 5. | Output noise of the low noise 45 V-4 A dual rail power supply (4 a load). |
Materials on the topic
- Datasheet EIC D15XB60
- Datasheet STMicroelectronics BD139
- Datasheet STMicroelectronics BD140
- Datasheet STMicroelectronics TIP35C
- Datasheet STMicroelectronics TIP36C