DC-DC converters are widely utilized in both hobbyist projects and industrial applications. The three primary types of non-isolated DC-DC converters are: buck, boost, and buck-boost. In this article/video, I present a compact DC-DC boost converter design using well-known components such as the UC3843 PWM controller, a Schottky diode, and an N-channel MOSFET. This design allows for input voltages as low as 9V, making it ideal for applications like converting 12V to 18V to power devices such as laptops from a single 12V battery.
The schematic and PCB design were created using Altium Designer 21, with component libraries sourced from SamacSys. The boards were fabricated with a green solder mask by Wellcircuits. I also measured the circuit’s noise characteristics using the Siglent SDS2102X Plus and SDS1104X-E oscilloscopes, along with a Siglent SDM3045X multimeter. Let’s dive in!
Specifications
Input Voltage: 9-16V
Output Voltage: Up to 28V (adjustable, see details below)
Output Current: 4A maximum
Output Noise (no load): 5mVrms
Output Noise (2A load): 27mVrms
A. Circuit Analysis
Figure 1 presents the schematic of the DC-DC boost converter. The heart of the circuit is the UC3843 chip, which controls the power conversion process.
Figure 1
Schematic diagram of the UC3843-based DC-DC boost converter
The components C1 and C2 serve to filter input noise, while L1, D1, and Q1 form the boost converter network. L1 is a 100µH inductor rated for 8A to 10A, and D1 is the MBR20100CT Schottky diode, which integrates two diodes in parallel for improved current handling. Q1 is an IRFZ44 N-channel MOSFET, which boasts a low ON resistance (RDS(ON)) of around 28mΩ and can handle up to 50A at 25°C. These characteristics make the chosen components highly suitable for this design.
The UC3843 PWM controller (IC1) is central to this boost converter. According to its datasheet, the UC3842/UC3843 series are fixed-frequency, current-mode controllers designed for off-line and DC-DC applications. The integrated features of the UC3843 include a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, a current-sensing comparator, and a high-current totem-pole output capable of driving a power MOSFET.
To minimize output noise, capacitors C3, C4, C5, C6, and C7 are employed. Boost converters typically generate more noise than buck converters, especially when using discrete components. A single-chip buck/boost controller may produce less noise but often has limitations in voltage and current handling.
R1 is a 10kΩ multi-turn potentiometer, allowing for precise adjustment of the output voltage. The output voltage is determined using the following formula:
Vout = 2.5 (1 + R1/R5)
When R5 is set to 1kΩ, the output voltage is in the range of 27V to 28V. By reducing R5 to 820Ω or 680Ω, the output voltage can be increased to around 32V to 33V, or 39V to 40V, respectively. However, caution is advised when exceeding this range as it may push the voltage and noise levels beyond the tolerances of the capacitors (typically 50V), potentially causing instability or failure due to manufacturing variations. Resistors R2 and R3 form a parallel load to help stabilize the output voltage.
B. PCB Layout
Figure 2 displays the PCB layout for the boost converter. It is a double-sided PCB with a mix of SMD and through-hole components, including views of the top and bottom layers, as well as the silkscreen and solder mask (top layer).
Figure 2
PCB layout for the DC-DC boost converter
The schematic and PCB were designed using Altium Designer [4]. During the design process, I encountered a lack of schematic symbols, PCB footprints, and 3D models for certain components. To avoid time-consuming manual creation and potential errors, I used the free SamacSys component libraries, which are IPC-standards-compliant. These libraries were imported directly into the Altium project using the SamacSys plugin [5]. SamacSys offers plugins for a wide range of PCB design software [6], not just Altium Designer, as shown in Figure 3.
Figure 3
Supported PCB design software with SamacSys plugins
For this project, I used SamacSys libraries for IC1 [7], Q1 [8], and D1 [9], as referenced. Alternatively, you can download component libraries from componentsearchengine.com and import them manually. Figure 4 illustrates the components selected in the SamacSys Altium plugin.
Figure 4
Selected components in the SamacSys Altium plugin
C. Assembly and Testing
Figure 5 shows the assembled PCB, both top and bottom views. This is the prototype of the circuit, and in the final revision, I included two parallel resistors to serve as a preliminary load. The board uses a mix of through-hole and SMD components, which should not pose significant soldering difficulties. However, you can order a pre-assembled board if preferred.
Figure 5
Assembled PCB (top and bottom view)
Two key parameters are critical when evaluating voltage regulators: line regulation and load regulation. Line regulation refers to the ability of the power supply to maintain a stable output voltage despite variations in the input voltage. Load regulation refers to the power supply’s ability to maintain the output voltage within specified limits despite changes in the load. These parameters are tested using a DC load. At the time of writing, I am awaiting delivery of the Siglent SDL1020X-E DC load [10] to conduct further detailed tests on this converter. For now, I have measured output noise levels.
Figure 6 shows the output noise under no load conditions, measured with the Siglent SDS2102X Plus oscilloscope [11]. The waveform displays some high-frequency spikes, likely due to long
