Introduction

引言

So far we’ve discussed a lot of the operational details of an H-bridge. We’ve seen what the basic operating modes are, how to select the power components, how to drive and how to control the bridge. This is enough to build and operate an H-bridge. And also enough to destroy it.

到目前为止，我们已经讨论了 h 桥的许多操作细节。我们已经看到了基本的运行模式是什么，如何选择电力部件，如何驱动以及如何控制H桥。这些知识足以制造和操作一座 H 桥。也可以摧毁它。

In this article I will concentrate on how to make the operation of the bridge safe. I will explore ways to safeguard the elements of the bridge itself. I will look into how to protect its power supply and the motor. I will also talk about what to do to protected the mechanical environment in which the bridge (and the motor) operates as well.

在本文中，我将集中讨论如何保证H桥的安全工作。我将探索如何保护H桥本身的元件、如何保护电源和电机。此外，我还将讨论如何保护机械环境中工作的H桥(和电机)。

In many cases the described protection techniques are contradictory: if you want to protect the bridge for example, you might not be able to provide a safe mechanical state at the same time. Of course you can argue that a destroyed bridge won’t provide much in terms of mechanical safety either, still judicious selection of which techniques to use and when is important and should be tailored to the specific application.

在许多情况下，所描述的保护技术是无法两全其美的: 例如，如果你想保护H桥，你可能就无法提供一个安全的机械状态。当然，你可以争辩说，故障的H桥在机械安全方面也不会提供太多的帮助---- 因此要明智地选择使用哪种技术，判断何时使用是很重要的，应该具体情况具体分析。

Over-temperature detection

安全温度检测

We’ve talked a lot about heat dissipation and techniques to minimize and evenly spread it across all the power elements of the bridge. Whatever you do however, it’s unavoidable that – when used outside of the design parameters – the bridge would over-heat.

我们已经讨论了很多关于散热最小化和均匀将其分散到H桥的所有功率元件上的技术。然而，无论你怎么做，它都是不可避免的，当使用外部的设计参数，H桥会过热。

There are some run-away conditions inside a bridge that makes temperature-monitoring even more important: as the FETs heat up, their channel resistance (rdson) gets higher. If they still delivering the same current – because of closed-loop current-control for example – the increased resistance will increase the heat-dissipation, which in turn will heat the FETs up even more. This positive feed-back eventually over-heat and destroy the bridge.

H桥中存在一些不稳定的条件，这使得温度监控变得很重要: 当场效应晶体管升温时，它们的等效阻抗(rdson)会变得更高。如果通过相同的电流-例如：因为闭环电流控制，电流不变，增加的电阻将增加额外的热量，这反过来又将加热场效应管。这种正反馈最终会使元器件过热并破坏H桥。

Detecting the temperature of the power elements (the FETs and the catch diodes) can be quite simple, especially if all of them are mounted on a single heat-sink. Simply attach a heat-sensor, like a the TMP35 from Analog Devices to the heat-sink and monitor the temperature either in the analog or (through an A/D converter or by choosing a digital-output sensor) in the digital domain. Sounds simple enough.

检测功率元件(MOS管和二极管)的温度非常简单，特别是当它们使用单个共同的散热器时。只需在散热器上安装一个热传感器，例如 Analog Devices 公司的 TMP35，并在数字域内监测模拟(通过 A/D 转换器或选择数字输出传感器)温度。

In practice attaching this extra element to the heat-sink is error-prone – what if it comes loose? – and might not even be possible if the FETs have individual heat-sinks or no heat-sink at all in the case of surface-mounted designs. You can of course add four sensors, one by each FET, but that adds complexity.

在实践中，将这个额外的元件附加到散热器是容易出错的——如果散热器松动了怎么办？如果场效应管有单独的散热器或者根本没有散热器，那么在表面安装是不可能的。你当然可以添加四个传感器，每个 FET 布置一个，但这增加了系统的复杂性。

There’s another way though, if precision is not your primary concern: as we’ve discussed rdson increases with temperature on the FETs. Consequently if you can measure the current through the FET and it’s voltage drop (Vds). You can figure out its resistance and from that you can determine its junction temperature. Even better: if all you need is to stay within safe limits, you can set your trigger on Vds alone, and just assume the maximum allowed current all the time.

不过，如果精度不是你首要关心的问题，还有另外一种方法可以测量温度: 正如我们已经讨论过的，表面温度随场效应管温度的升高而升高。因此，通过检测场效应管的电流和它的压降(Vds)。就可以计算出它的电阻，然后你可以确定它的结温。更理想的情况是: 如果你所需要的只是保持温度在安全的范围内，你可以单独在 Vds 上设置触发器，并且触发值为允许的最大电流。

For example, if you use the IRF1010Z FET, it has 7.5mΩ on-resistance at room temperature, and roughly twice of that at 170oC:

例如，如果你使用 IRF1010Z FET，它在室温下有7.5 mΩ 的导通电阻，在170 °c 时这个值大约是两倍:

Battery Reverse Connect Protect

电源反接保护

The idea is that when the battery is connected with normal polarity, it will forward bias the body-diode of Q5, driving its source to Vbat. When that happens, the grounded gate will close Q5 (it’s a P-channel device), making it capable of handling large(er) currents.

如图1所示，当电池与正常极性连接时，Q5的寄生二极管将正向导通，将其源极驱动到 Vbat。当这种情况发生时，栅极接地，Q5将被打开(它是一个 p 通道MOS) ，使其能够处理更大电流。

When the battery is connected in reverse, the diode is reverse-biased, leaving the gate and the source of Q5 at the same potential, keeping the Q5 open, and the rest of the system un-powered.

当电池反向连接时，二极管反向偏置，使栅极和 Q5源极处于同一电位，保持 Q5处于关闭状态，系统其余部分不供电。

The value of R1 should be high (100k or so) because in normal operation it’s connected between Vbat and GND. Finally, if Vbatcan be higher than the maximum allowed VGS for Q5 (15-20V normally) limiting the gate-source voltage will be needed:

R1的阻值很高(100k左右) ，因为在正常运行时，它连接着 Vbat 和 GND。最后，如果 Vbat 高于 Q5(通常为15-20V)允许的最大 VGS，则需要限制栅极-源极电压:

Here, under normal operation D5 will limit VGS to be within safe limits with some current flowing through R1. In reverse operation, R2 ensures that Q5 can’t close. The value of R1 should be select to set the appropriate zener current (a few mA). R2 should be large enough so it doesn’t interfere with the voltage limiting effect of D5 under normal circumstances.

如图2，在正常工作情况下， D5将 VGS 限制在安全范围内，一些电流流过 R1。在反向操作中，R2确保 Q5无法关闭。应该选择适当的R1的值来设置齐纳电流(几毫安)。R2应该足够大，这样它就不会干扰 D5在正常情况下的电压限制作用。

All these circuits used a PMOS device to achieve reverse-battery protection. If you want to use an NMOS device to take advantage of its lower rdson, you have to put it on the low-side of the bridge:

所有这些电路都采用 PMOS 器件实现蓄电池反接保护。如果你想使用 NMOS 设备，因为它具有较低的 rdson，你必须把它放在H桥的低端:

What you have to be careful about though, if you employ any of these techniques is that you have to protect the whole circuit, not just parts of it. It’s not enough to protect the power FETs. The driver circuitry, and the large electrolytic input filter capacitors are also sensitive to reverse battery connection. Don’t make the mistake that the MonsterMoto Shield guys did. Their protection circuit (Q1 and Q2) protects the bridges and the drivers (U1 and U2), but not the input capacitors (C2, C3, C5, C6). Those can easily explode if you connect the battery in reverse!

但是，如果你使用这些技术中的任何一种，你必须小心，应该保护整个电路，而不仅仅是部分电路。光保护功率场效应管是不够的。驱动电路和大型电解输入滤波电容器对电池的反接也很敏感。不要犯那些错误。它们的保护电路保护H桥(Q1和 Q2)和驱动器(U1和 U2) ，但不保护输入电容器(C2、 C3、 C5、 C6)。如果你反接电池，它们会爆炸！

Limit-switches

限位开关

When your motor drives something that has only limited travel (say an elevator) you really want to make sure that your load isn’t driven over the end.

当你的马达驱动的东西，只有有限的行程(比如电梯) ，你需要确保你的负载不超行程。

The easy part of the assurance is to include switches at each end of the allowed range that signal whenever your load is touching them.

简单的事情是，你可以在允许行程范围的内设置接近开关，每当您的负载接触他们时会产生信号。

The hard(er) part is to make sure that your motor in fact stops when the switches signal. The trouble lies in that the action you take – while in theory the same – in practice depends on the drive-mode of the bridge.

困难的部分是如何确保您的电机实时停止，当开关信号长产生时。问题在于你所采取的行动——理论上是一样的——实际上取决于H桥的驱动方式。

Want to make sure of is that whenever the forward limit switch is on, your only allow the motor to spin in the reverse direction. Similarly, the reverse limit switch – when on – should limit operation to the forward direction.

要确保的是，每当正向限制开关被打开，只允许你的电机在相反的方向旋转。同样，反向限位开关触发时，应限制电机向前操作。

In the sign-magnitude drive modes you have a separate signal telling you the intended direction. So what the limit switches should do is to make sure that the PWM input is forced to 0% duty cycle if the direction signal is pointing in the wrong way.

在符号-幅值驱动模式中，你有一个独立的信号告诉你电机的预期方向。因此，如果方向信号指向错误的方向，限位开关应该做的是确保输入的PWM的占空比为0% 。

For lock anti-phase drive mode, the direction is encoded in the PWM signal as well. So the action should be the following:

对于锁定-反相驱动模式，方向也被编码在 PWM 信号中。因此，应该采取以下行动:

• The forward limit switch should limit the PWM signal to never go beyond 50%, when on
• 前向限制开关应限制 PWM 信号永远不超过50%
• The reverse limit switch should limit the PWM signal to never go below 50%, when on
• 反向限制开关应限制 PWM 信号永远不要低于50%

This simple action might not be enough though: as the load travels towards the limit switch and actuates it, all that happens is that the motor abruptly changes from forward (let’s say) to stationary operation. This will in some uncontrolled way slow down and eventually stop the load. During this transient you might have all kinds of problems, like too much travel or too much torque and there isn’t much you can do about them. It would be better for example if you could drive the motor backwards to further reduce the travel overshoot or gradually decrease the forward drive to zero to limit the torque. In order to do these you will need to essentially tie in the limit switches to the control loop of the motor.

这个简单的控制动作可能还不够: 当负载触发行程开关，电机的状态突然变化，从前进(假定)到静止的操作。电机将以不受控制的方式放慢速度，并最终停止负载。在这个过渡过程中，你可能会遇到各种各样的问题，比如超出了太多的行程或点击具有太大的扭矩，而你对此无能为力。例如，如果你可以驱动电机向后运动以进一步减少行程超调或逐步减少向前驱动到零来限制扭矩，这将是更好的办法。为了做到这一点，你基本上要把限位开关连接到电机的控制回路上。

However doing that isn’t without dangers either. As you make the reaction to a danger signal more and more complex, the more likely it is that something in your reaction will go wrong and bad things happen. You might want to include several levels of protection for example: one set of limit switches that trigger a soft-stop operation through the control circuit and another fail-safe set that shuts down the bridge through the previously described control-signal override mechanism.

然而，这样做也并非没有危险。当你对危险信号的反应越来越复杂时，你的反应越有可能出错，这会导致坏事发生。例如，您可能需要包括多个级别的保护：一组限位开关通过控制电路触发软停止操作，另一组通过前面描述的控制信号，关闭电桥。

Summary

摘要

In this post we’ve went through a lot of potentially dangerous situations for an H-Bridge. We’ve talked about how to detect them and how to react to them when they occur.

在这篇文章中，我们涉及了很多潜在的H桥的危险。我们已经讨论了如何检测它们，以及如何在它们发生时作出反应。

Some of the introduced techniques are contradictory (for example sometimes I suggest you included a fuse, in other cases I’ve adviced against it). When you build a bridge, you always have to examine the use-cases and determine which of the potential problems are real and which ones are not likely to happen.

这里介绍的一些技术是互相矛盾的(例如，某些情况下我建议你电路中应该包括一个保险丝，但在其他情况下，我反对这样做)。当您构建一个H桥时，你需要检查使用环境，并确定哪些问题是潜在的，哪些是不可能发生的。

In the next installment of the series I’ll look into closed loop control techniques to implement constant torque or constant velocity controls.

在本系列的下一期中，我将研究实现恒转矩或恒速控制的闭环控制技术。

Continue

译者续

原作者文章更新至此，译者未找到作者所言的后续文章，文章发布时间很早，想联系作者也不太可能了。这一系列对H桥的讲解足够透彻，能够使读者醍醐灌顶。

原作者的很多技术信息十分经典，但随着技术发展，现在已经有了更多的技术方法和保护机制，译者将会继续更新这系列文章，介绍最新一些的有刷电机驱动技术。感谢很多忠实读者对这一些列文章的支持，翻译校正不易，希望后续我写的文章，也能给你带来收获。

下一篇文章也是H桥的保护机制，我将会在这篇文章中介绍如何削弱电机反电势灌入电源，或者在电机极速制动时，如何回收电机产生的能量（与之前的电容吸收方式不同）。

另外，欢迎催更，毕竟我是一个随性的人儿~，email：109549791@qq.com