1kV power supply capable of producing continuous arc

设计一种能够产生连续电弧的高压开关电源可能是具有挑战性的。这种小巧高效的开关电源在输出功率为 20W 时可输出 1kV电压，并能耐受连续电弧（即短路）（图 1）。它使用标准的市售元件。使用R1将开关稳压控制器LTC1871设定在120kHz的额定工作频率。该电路像间断式回扫电路一样工作，在 C1上产生 333V 电压。二极管/电容器电荷泵倍增器把该电压升高到三倍，在输出端产生1000V 电压。图 2 示出了该电路产生的开关波形。当初级开关 Q1 导通时，输出整流器被反向偏置，能量存储于变压器 T1 中。当 Q1 截止时，能量传输到次级线圈，C2 和 C3 通过整流器提高输出电压。初级电压升高，并通过变压器和整流器 D1 箝位为C1上的电压。变压器耦合良好，所以漏电感几乎不会造成电压尖脉冲。跨接在初级线圈上的小型 RC阻尼器可衰减阻尼振荡，并降低 EMI（电磁干扰）。

To provide current limiting protection, the circuit shown in Figure 1 contains two active circuits and one passive component. The voltage across current sense resistor R2 limits the peak primary current to 7.5A. Q2 provides secondary current limiting. Note the bump on the leading edge of the current rise in waveform 2 in Figure 2. This bump coincides with the positive excursion of the voltage across R3 in waveform 4, which is the refresh current for C2 and C3. When the circuit is overloaded, this current bump is large enough to enhance Q2 and thus fold back the load current (Figure 3). The power dissipation caused by a hard short circuit is relatively low. Without Q2 for secondary current limiting, the short circuit current and internal power dissipation are greatly increased, resulting in the failure of the primary switch Q1. R4 provides load impedance for the power supply.

This load helps limit the peak current stress in the multiplier capacitor and diode. Do not derate R4, as the power dissipation during continuous arcing can be significant. If R4 fails to disconnect, the feedback circuit will force a full duty cycle with disastrous consequences. Too low a value for R4 can lead to a burned-out circuit and hours of debugging. Arcing is most stressful, with the output capacitors constantly charging and discharging (Figure 4). As a final figure of merit, the circuit's efficiency is high (Figure 5). At 12V input voltage and 20W full load, efficiency reaches 87.3%, rising to 87.7% at 24W overload.

So what applications would this circuit be good for? Maybe a battery-powered bug zapper. And, like running the live wire across a grounded filing cabinet, this would be a great tool for muting the AM radio on a manufacturing floor. This circuit probably doesn't provide enough power to be used as an ionizer for a plasma cutter, but one engineer I know is willing to give it a try. An older version of this circuit used a monolithic switching power supply and materials that fit into a banana connector, and produced a bright orange glow and enough heat (and plenty of ozone) to spark the idea of ​​using it as a fire extinguisher.

作者:Robert Sheehan，Linear Technology，Milpitas，CA