How does a boost converter increase DC voltage?

A boost converter stores energy in an inductor's magnetic field and transfers it to the load through a switching circuit. When the switch closes, current flows through the inductor, increasing linearly and storing energy. When the switch opens, the inductor's polarity flips and adds to the input voltage, producing a higher output potential. This energy transfer enables voltage step-up in a single stage.

What role does the duty ratio play in boost converter output?

The duty ratio, defined as the ratio of switch on-time to the total period, directly controls the output voltage. As duty ratio increases, output voltage increases proportionally. Ideally, a duty ratio of 0.2 produces 12.5 volts from a 10-volt input, while 0.6 produces 25 volts. However, parasitic elements limit practical duty ratios to approximately 0.7 or 0.8 maximum.

What components make up a basic boost converter circuit?

A boost converter consists of an input DC voltage source, an inductor, a switch (MOSFET or transistor), a blocking diode, and a capacitor. The switch alternately connects and disconnects the inductor from the power supply. The diode prevents reverse current, while the capacitor filters output ripple voltage. Increasing capacitance decreases ripple and produces steadier DC output.

How does switching frequency affect boost converter performance?

Higher switching frequencies allow the capacitor's charge and discharge cycles to complete quickly, reducing output voltage ripple. At sufficiently high switching frequencies, the output reaches steady-state voltage with minimal ripple. The pulse train frequency, typically 100 kilohertz in experiments, determines how rapidly the inductor charges and discharges energy to the load.

What happens to inductor current during boost converter operation?

Inductor current forms a triangle wave pattern. During the switch on-time, current ramps up linearly as the inductor connects to the supply voltage. During the switch off-time, current ramps down linearly as the inductor transfers energy to the load. The offset represents the average current. This continuous cycling in continuous conduction mode ensures non-zero inductor current throughout operation.

Why are boost converters used in battery-powered systems?

Boost converters step up variable or low DC voltages to higher levels without converting to AC or using transformers. In battery systems, stacking many cells to achieve desired voltage requires significant space. Instead, boost converters efficiently increase voltage from fewer cells, conserving space and simplifying design. They also regulate variable solar panel output to consistent grid-compatible voltages.

What limits the maximum output voltage in a practical boost converter?

Parasitic elements and resistances in the circuit limit useful duty ratios to approximately 0.7 or 0.8, preventing the theoretical infinite voltage at duty ratio one. When duty ratio becomes sufficiently large, parasitic effects dominate circuit operation and output voltage actually decreases despite increasing duty ratio. Practically, output voltage is limited to about three or four times the input voltage.

DC/DC升压转换器

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注意：本实验设计将输出电压限制在 50V 直流以下。仅可使用本文中给出的占空比、频率、输入电压或负载。

本实验将使用 HiRel Systems 公司提供的 DC-DC 转换器板。http://www.hirelsystems.com/shop/Power-Pole-Board.html

有关该电路板操作的信息可在此系列视频“HiRel 电路板简介”中找到。

此处展示的步骤适用于任何可在原型板、面包板或印刷电路板上搭建的简单升压转换器电路。

1. 板卡设置：

在“DIN”连接器上接入±12信号电源，但保持“S90”处于关闭状态。
确保PWM控制选择器处于开环位置。
将直流电源设置为10 V。
1. 目前先保持输出端与电路板断开连接。
在连接负载电阻之前，将其调节至20 Ω。
使用下管MOSFET、上管二极管和BB磁性电路板搭建图2所示电路。
1. 注意电路板上标注的电感值。
将“R_L”连接在“V1+”和“COM”之间。
1. 注意，与降压变换器实验相比，输入和输出连接方式是相反的。
2. 切勿在实验过程中断开负载，因为升压变换器可能变得不稳定，导致电路板损坏。
3. 确保MOSFET选择（下管MOSFET）、PWM选择及其他设置的开关阵列配置正确，以实现如图2所示的功能电路。

开关电路图：(a) 基本型，(b) 添加二极管型，(c) 二极管-电容配置。
图 2．升压转换器电路

2. 调整占空比和开关频率

将差分探头连接至下管MOSFET的栅极与源极之间。
打开“S90”开关，示波器屏幕上应出现开关信号。
1. 调节信号时间轴，使屏幕上显示两到三个周期。
2. 调节频率电位器，使频率达到100 kHz（周期为10 µs）。
调节占空比电位器，使占空比达到10%（导通时间为1 µs）。

3. 可变输入的升压变换器测试

将已设置为 10 V 的输入直流电源连接至“V2+”和“COM”。
连接差分探头以在“CS5”处测量电感电流。
1. 将另一个探头跨接在负载两端。确保接地端连接至“COM”。
2. 捕获波形，并测量输出电压平均值、电感电流纹波以及电感电流平均值。
3. 记录直流电源上的输入电流和电压读数。
将输入电压调整为 8 V、12 V 和 14 V，并对每个电压值重复上述步骤。
断开输入直流电源，并将其输出调整为 10 V。

4. 可变占空比的升压变换器测试

将差分探头连接至下管MOSFET的栅极与源极两端。
1. 将另一个探头连接至负载两端。确保接地端连接到“COM”端。
2. 将输入直流电源连接至“V2+”和“COM”端。
3. 采集波形，并测量输出电压的平均值以及栅源电压的导通时间（即占空比）。
4. 记录直流电源上的输入电流和电压读数。
将占空比分别调节至20%、40%和60%。对这三个占空比分别重复上述步骤。
将占空比重置为10%。
断开输入直流电源。

5. 可变开关频率的升压变换器测试

将差分探头连接至下管MOSFET的栅极与源极两端。
将另一探头跨接在负载两端，探头接地端连接至“COM”端。
将输入直流电源连接至“V2+”和“COM”端。
调节开关频率至70 kHz。
采集波形，并测量输出电压的平均值以及栅源电压的导通时间（即占空比）。
记录直流电源上的输入电流和电压读数。
将开关频率分别调节至40 kHz、20 kHz和10 kHz（若无法达到10 kHz，则调至可实现的最低频率）。
对上述三种开关频率，依次重复执行前述步骤。
关闭输入直流电源和“S90”开关，然后拆解电路。

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来源：Ali Bazzi，康涅狄格大学电气工程系，斯托尔斯，康涅狄格州。

升压变换器为许多需要提高直流电压的应用提供了一种灵活的解决方案，无需将直流电压转换为交流电，再通过变压器升压并整流变压器输出。升压变换器是一种利用电感作为储能元件的升压型变换器，该电感在直流输入电源的基础上向输出端提供额外能量…

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