驅動和保護電源開關的高級解決方案?

如今，新的功率開關技術正被廣泛應用于要求高功率密度、高開關頻率和小尺寸是關鍵要求的苛刻應用中。這些新開關器件發(fā)揮作用的三個關鍵應用是：?

汽車（牽引逆變器、DC/DC 轉換器和車載充電器）?

工業(yè)/電機控制（負載點電源、不間斷電源、機器人、電機控制）?

電源/太陽能（太陽能逆變器、電信電源、服務器/云/PC電源）?

功率開關要么使用傳統(tǒng)的硅基技術制造，例如MOSFET和絕緣柵雙極晶體管 (IGBT)，要么使用更新的寬帶隙半導體制造，例如碳化硅和氮化鎵。在相關應用中，汽車是近年來發(fā)展勢頭強勁的領域，主要是由于正在向電動汽車過渡以及電動汽車的逐步采用。?

如圖 1 所示，電動汽車集成了大量傳感器和電子電路，包括高壓總線（400 V、800 V 或更高）和本地低壓總線。SiC 器件正在取代高壓系統(tǒng)中的硅基器件，例如車載充電器、電池管理系統(tǒng)、主 DC/DC 轉換器和牽引逆變器。?

圖 1：電動汽車系統(tǒng)中的開關技術?

高壓母線存在嚴重的安全問題，它必須與低壓母線電隔離，同時仍允許在兩個電壓域之間雙向交換信息。?

Skyworks 隔離柵極驅動器

Skyworks Solutions 是一家為無線網絡應用提供高度創(chuàng)新的模擬半導體的領先公司，最近完成了對 Silicon Labs 基礎設施和汽車業(yè)務的收購。針對包括電動汽車和混合動力汽車在內的關鍵汽車領域的增長，Skyworks 為硅、GaN 和 SiC 電源開關提供高性能和強大的隔離式柵極驅動器。?

Skyworks Solutions 產品經理 Charlie Ice 在 2021 年 PowerUP Expo 上舉行了關于“驅動和保護未來的電源開關”的技術演講，討論了硅基和寬帶隙功率器件的關鍵柵極驅動器要求和保護方法. 本文將介紹相同的主題。?

“特別是在電動汽車中，我們必須確保高壓側和低壓側保持隔離，同時確保它們仍然可以通過該屏障進行通信和信息交換，”查理說。?

隔離器件的特性對于 SiC 和 GaN 等新的開關技術更為重要，它們可以實現更高的效率，但更敏感，更容易損壞。因此，這些新的開關技術需要獨特的保護才能安全可靠地運行。?

傳統(tǒng)上，電力電子系統(tǒng)依賴于 IGBT，這是在高功率和高電壓條件下每瓦成本最低的解決方案。然而，IGBT 的開關速度較慢，從而限制了系統(tǒng)的效率。這就是 SiC 和 GaN 都介入以真正推動更高效率的地方。兩者的一個缺點是它們不能像 IGBT 那樣承受盡可能多的故障條件，這就是它們需要額外保護的原因。?

在高壓系統(tǒng)中，為了安全起見，我們必須將高壓側與低壓側分開。通常，設計人員決定將控制器保持在低壓側，以便遠離噪聲和大瞬態(tài)。控制器生成脈寬調制 (PWM) 信號，并將它們穿過隔離柵傳遞到柵極驅動器，該驅動器基本上將低壓 PWM 信號放大為能夠打開和關閉功率器件的更高信號。?

隔離式柵極驅動器執(zhí)行的兩個主要功能是將 3V 或 5V 信號電平轉換到 24V 或 30V 的較高電壓軌，并提供開關電流以對柵極電容器進行充電/放電。通過添加電流隔離屏障，該器件實現了兩個主要優(yōu)點：?

It provides input-to-output isolation for protection of the controller, and perhaps personnel, from high voltages and voltage transients.?

It helps to maintain noise-immune operation for best efficiency. High-voltage transients can disrupt operation, resulting in loss of modulation and thus efficiency.?

The isolated gate driver can be safely used to switch even high-power switches, such as silicon or superjunction MOSFETs, IGBTs, and wide-bandgap switches like GaN and SiC. Isolated gate drivers are available in many flavors: single-channel, dual-channel, and ones that can generate a high-side and a low-side signal from a single PWM input.?

“I typically find that many automotive systems use single-channel drivers because they make the board-layer layout easier; however, dual-channel drivers and high-side/low-side drivers are very popular in power supply systems,” said Charlie.?

Regarding protection, one of the key methods is the Miller clamp. Its function is to monitor the voltage on the gate, and if it gets too high, it clamps it. Basically, it’s an active monitor to ensure the gate is always off. However, Miller clamp protection is not enough for SiC and GaN power devices, which are more sensitive and get damaged more quickly. The other feature we need to add for driving SiC or GaN devices, improving their protection and longevity, is desaturation detection and soft shutdown.?

In a high-power system, such as a traction inverter, it’s not uncommon that power devices experience a momentary overcurrent condition. In this case, an isolated gate driver with desat detection can monitor the voltage (VCE) across the power switch. If it detects too much voltage across it (see Figure 2), which would indicate a fault condition, it automatically shuts it off in a very safe way, also known as soft shutdown. However, it is important to set the device off quickly enough to avoid being damaged. Here, we can see how switching devices behave differently. An IGBT, for instance, needs to be turned off within 3 μs, while a SiC device needs to be shut down within 1.2 μs and a GaN device within 200 ns.?

Figure 2: Desaturation protection with fault indication?

“這兩項關鍵技術——米勒鉗位和去飽和檢測——對于成功驅動 SiC 和 GaN 以及使系統(tǒng)可靠并且在許多方面安全，已經變得非常關鍵，”Charlie 說。?

審核編輯：劉清