Page 2 : 簡易電路 (續) Simple Circuits - Continued

[Previous] [Next]

原文：http://www.totallyamped.net/adams/page2.html

首先，我要解釋一下 Back EMP (BEMP) 和 Back Emf (BEMF)。 BEMP 是反電動電勢 (Back Electromotive Potential)，而 BEMF 是反電動勢 (Back Electromotive Force)。 有何差別呢? 力的度量為質量x加速度 (mass x acceleration)。這意味著質量的運動為力的整體的一部分。在電子電路中，質量的運動為 "電流"。 Whilst there is a lot of debate about whether electrons actually move, or whether their electron "charge" is the only movement in the form of charge energy transfer from atom to atom, the notion of movement is still paramount to the formula of calculating force. For simplicity sake, we will assume that there is movement of some sort and leave it at that. 所以當我們提到 BEMF，意味著具有電荷移動，其方向與 Forward EMF (FEMF 提供電流)相反。 BEMP 為 Back Electromotive Potential。只要有任何的 BEMF 產生，必然有 BEMP，但反過來則不一定成立。稍後我將在後面的page 討論 Collapsing EMP (CEMP) 及 Collapsing EMF (CEMF)。

On page 1- I wrote : - "除此之外，通常，快速旋轉的磁鐵掃過線圈，也會感應電動勢 ( ElectroMotive Force) 回到線圈，其方向與輸入的供應電流是相反的。此相反方向的 EMF 即所謂的 Back EMF，會發生在所有的傳統馬達，不管是那一類型的馬達。然而，在上面的電路中，此 BEMF 是無法再降低輸入電流的，我會在後面更進一步說明為何會如此。"

在下面的 Fig 3 中，Circuit A 是前面的 page 已提到過的，而旁邊的 Circuit B 則代表傳統的 DC 馬達。參見下面的 Fig 3 來解釋圖中畫的電流路徑的差異。

在上面 Fig 3 中的 Circuit B，將一般的 DC 馬達接上電源，轉速迅速地增加至最高速度。在此過程，會發生 BEMP，其將產生 BEMF。此 BEMF 就像 Forward EMF (FEMF)，電路中有完全的迴路供其流動。它絕不會像 FEMF 一樣大，所以測量到的淨電流的流動總是和電源電流的方向。但是上面 Fig 3 中的 Circuit A，會發生 BEMP，但不會引發 BEMF，因為電晶體 Q1 對供應電流而言是正偏壓，但對BEMF而言是逆偏壓，因此它會擋住任何反方向的電流。因為這樣，只有增加由脈衝頻率形成的阻抗，會降低流過線圈的電源電流。現在接著看下面的 Fig 4，其顯示如何在電路中利用 BEMF 來更進一步降低電源電流。參見下面的 Fig 4 來顯示電路的差異和做解釋。

在上面的 fig 4 中，兩個電路是一樣的，只是在Circuit B 中，在集極與射極之間多了跨接的二極體 D1。現在這二極體可以提供 BEMF 的電流迴路，而且可以使供應電流再降低一些。在高阻抗線圈馬達中，因為它的電流已經相當低了，你可能不會注意到電流的顯著變化，但是當馬達的設計為了要提供更多轉矩時，會使用低阻抗的線圈，多加的二極體搭配此線圈阻抗可以顯著地減少供應電流。 Now it also must be said, that the addition of Diode D1 will also effect to some degree the amplitude of voltage "spikes" occuring in the system which are due to the Collapsing EMP of the coil from the pulsing it receives. Normally this is a good thing, because these spikes are generally considered to be bad news, and in conventional systems, they are usually "bled out " of the system in one way or another. If however, these spikes are what you want because of the nature of the experiments you are performing, then simply leave the diode out. Now if you are basing your circuit on the very simple ones shown thus far, and you are not getting high voltage spikes (and you want to), it is likely, that the control circuit needs a bit of fine tuning, to ensure that when the Hall IC is in the "off" mode, your transistor is completely turned "off" and not just switching between states of "slightly on" and "completely on". 在下面的 Fig 5 繪示了一些電晶體偏壓控制的基本作法，請參照下面的 Fig 5 來作電路說明。

在上面 Fig 5 的 Circuit A 中，在 Hall IC 的開關輸出與電晶體 Q1 的基極之間加了一個可變電阻。 This allows some degree of flexibilty in "tuning" the voltage that is applied to the base of Q1. The VR1 (linear Pot - lets say 1000 ohms) as shown, acts as a voltage divider, and the value of the voltage that feeds the base of the transistor is proportional to the position of the the wipe contact in relation to the resistive track of the VR1. If the voltage from the Hall IC output to the top of the VR is 1Volt and the wiper contact is exactly halfway, then the voltage fed to the base of Q1 would be .5 V and Q1 would not turn on. If the wiper is moved towards the top of VR1 the voltage will increase towards 1 Volt and Q1 will turn on when it reaches above .6 Volts(for silicon Transistors). This method offers some flexibility but has the disadvantage that some control circuit current will be shunted to Ground via VR1 and some current will be lost to Q1 even if the VR1 wiper is as the top of the VR1 resistive track. If the current loss is too high due to the value of VR1, then Q1 may still not turn on when required, even when the voltage available is high enough, because transistors are current driven and require a minimum amount of current to "turn on". However, this method should suffice for most experimental purposes, and is very simple to implement. I will address the current loss problem associated with the VR1 in Fig 6.

在上面的 Fig 5 的 Circuit B 中，小訊號二極體與 Hall IC 的輸出串聯。每個二極體會產生壓降，對矽二極體而言為 0.6 V，或對鍺二極體而言為 0.4 V。可以用這兩種型式互相搭配，得到所需的電壓降。The actual number of Diodes used will be dependant on the amount of Voltage dropping that is needed to make Q1 turn off completely when the Hall IC is in "off" mode. The advantage of this method, is that no current is shunted to ground, and there is minimal current loss through the diodes when the voltage rises above their total threshold conducting voltage when the Hall IC is switched to the "on" state. The disadvantage with this method is that it lacks runtime flexibility, and if the motor has been running for some time and the supply voltage begins to drop, there will be a point at which the forward bias voltage is no longer sufficient to turn Q1 on. In Fig 6 below, the advantages of both circuits are incorporated together to offer greater flexibility and increased stability, while an extra transistor is inserted (Fig 6 Circuit B) to address current loss problems associated with VR1. See Below Fig 6 for an explanation of the circuit modifications.

在上面 Fig 6 的 Circuit A 中， the previous circuits in Fig 5 have been combined to produced a more stable circuit which offers a degree of flexibiliy in controlling the amount of bias to Transistor Q1. However, depending on the type and characteristics of Q1, the voltage supplied to the base may be sufficient, but the available Base to Emitter junction current may now be too small to operate Q1 efficiently. 在 Fig 6 的Circuit B 中，電路中多加了一個較小的 NPN transistor (Q2)，構成一般稱為的 "達靈頓對 (Darlington Pair)" 的架構。 Because the added Transistor Q2 will add a .6 Volt drop to the base current circuit, one of the signal Diodes has been removed, so that the effective voltage dropping due to "silicon junctions" is effectively the same in both circuits. The advantage of adding Q2 however, is that when it turns "on" due to sufficient bias voltage, it allows extra current to flow to the base of Q1 via R2 and the Collector to Emitter junction of Q2. The amount of extra current available to the base of Q1 will be mostly determined by the value of R2. Circuit B now offers a stable and variable controlling circuit which protects all the controlling components, whilst allowing a greater "turn on current" to Q1, which in turn allows a greater current availability to the motor coil via the Q1 Collector to Emitter junction.

假如你照著上面的任一個架構來組裝實驗馬達電路，但沒有得到你預期的結果，像是，轉子轉得不快，不管轉子的轉速為何消耗的電流都相當大，等等，你可能要使用更高電阻值的 R1，或者加入更多個別的二極體，確保電晶體真的完全關閉。

下面的敘述的簡單測試方法，可供你可以用來確定電晶體 (或 Mosfet) 是否完全關閉：

1... 連接你的線路。

2... 在集極與射極之間跨接一個電壓計。 (不用管此電晶體為 NPN 或 PNP，或是線圈連接至那一支腳。)

3... 用手讓馬達停止轉動，然後再用手轉動馬達，直到 switching magnet 在 Hall IC 的前面，使得 Hall IC 導通。

4... 測量集極與射極之間的電壓。 - 假如 Hall IC 是在 "on" 的狀態，那麼集極與射極之間的電壓降應該只有 0.6 V。

5... 現在轉動轉子，使得 switching magnet 遠離 Hall IC，此時 Hall IC 應該是在 "off" 狀態。

6... 再測量集極與射極之間的電壓。 - 假如電晶體完全關閉，那麼電壓應該是幾乎全部的電源電壓減掉因線圈造成的少許壓降。假如測得的電壓並非幾乎等於電源電壓 (或是非常接近電源電壓), 那麼電晶體就沒有完全關閉。 - 補救方式是將電阻R1串接一個1K - 5K 的可變電阻器，並且重複測試 "導通" 的步驟 3+4 及 測試 "關閉" 的步驟 5+6。調整可變電阻器直到電晶體關閉。 - 你會知道它是關閉的，因為測得的電壓會幾乎等於電源電壓。

在上面電路的說明，主要都專注在電路的基本運作，忽略了大部分元件的實際數值。這是因為 VR1 及 R1/ R2 的數值，或是使用的個別二極體的數目，真的是要根據使用的Hall IC 和 電晶體 Q1 及 Q2 的型式及特性來決定。

在後面的 page，我要討論 Collapsing EMP/EMF，以及如何用它來對電容或其他電池充電，或者增加馬達的轉矩。我也要討論電壓穩壓器和 "Mosfets" 以及其用在電路切換上的優點，也會介紹更實用及更穩定的控制電路。

譯註: Hall IC 有兩種型式，一種是開關的型式，另一種為線性的型式。在此所用的應是線性的類型，才需要調校on/off的工作點。