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: 本实验旨在限制输出电压小于 50V DC。仅使用此处给出的占空比、频率、输入电压或负载。

本实验将利用 HiRel 系统提供的 dc-dc 转换板。http://www.hirelsystems.com/shop/Power-Pole-Board.html

有关主板操作的信息, 请在本集视频 "HiRel 板介绍" 中找到。

这里所示的程序适用于任何简单的升压转换电路, 可以建立在原始板, 面包板, 或印刷电路板。

1. 安装板:

连接±12信号供应在 "DIN" 连接器, 但保持 "S90" 关闭。
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. 现在将输出与主板断开。
在连接负载电阻之前, 将其调整为20Ω。
使用较低的 MOSFET、上二极管和 BB 磁板来构建图2所示的电路。
1. 注意主板上显示的电感值。
在 "V1+" 和 "COM" 之间连接 "R_L"。
1. 请注意, 与降压转换器实验相比, 输入和输出连接是翻转的。
2. 在实验中切勿断开负载, 因为升压转换器可能会变得不稳定, 并对主板造成损坏。
3. 确保开关阵列的 mosfet 选择 (低 mosfet), PWM 选择, 和其他设置是正确的, 以实现一个功能电路如图2。

图 2.升压转换电路

2. 调整占空比和开关频率

将差分探头连接到较低 MOSFET 的栅极源上。
打开 "S90"切换信号应出现在示波器屏幕上。
1. 调整信号时间轴以查看两个或三周期。
2. 调整频率电位器, 实现频率为100赫 (周期为10µs)。
调整占空比电位器达到10% 的占空比 (准时1µs)。

3. 可变输入的升压转换器测试

将输入的直流电源 (已设置为 10 V) 连接到 "V2+" 和 "COM"。
在 "CS5" 上连接差分探头以测量电感电流。
1. 将其他探头连接到负载上。确保接地接头连接到 "COM"。
2. 捕获波形并测量输出电压平均值、电感电流纹波和电感电流平均值。
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, 并对上述每个电压重复上述步骤。
断开输入直流电源, 并将其输出调整为 10 v。

4. 可变占空比的升压转换器测试

将差分探头通过栅极连接到下部 MOSFET 的源。
1. 将其他探头连接到负载上。确保接地接头连接到 "COM"。
2. 将输入直流电源连接到 "V2+" 和 "COM"。
3. 捕获波形并测量输出电压平均值和门到源电压的时间 (也为占空比)。
4. 记录直流电源上的输入电流和电压读数。
将关税比率调整为20%、40% 和60%。对上述三项工作比率中的每一项, 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转换器测试