[Practice every Monday] How to troubleshoot problems in the transistor drive control circuit?

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[Practice every Monday] How to troubleshoot problems in the transistor drive control circuit? [Copy link]

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A few days ago, a netizen y475199448y posted, [ What is the working principle of this anti-saturation drive circuit? ]

Recalling the post [ Analysis of Transistor Control Circuit ] by netizen Xiao Taiyang yy , I was looking for help and discussion on issues related to transistor drive circuits.

These problems sometimes involve some basic transistor drive control principles, so how to troubleshoot these problems? How to analyze the transistor control circuit?

Often in circuit design, including power circuit design, high-speed communication design, analog circuit design, etc., you will encounter commonly used transistor circuit design. How to choose the drive resistor? What is the working principle of the drive circuit? What are the working principles and base resistance of the transistor when it acts as a switch? How to perform [Triode Control Circuit Analysis] ? Etc.

Looking through the classic textbooks or books on electronic technology, there will be all kinds of amplification circuits, common base, common collector, common emitter, etc., and the related calculation formulas, curves, and circuit equivalent models are all over the place...

However, in the age of digital circuit-controlled electronic technology, we often encounter some problems related to the use of transistors as switching circuits, especially when using the IO port of a microcontroller to control a low-power device, such as a buzzer, relay, LED light group, etc., which are when using transistors as switches.

As shown in the figure below, the transistor can either work in the saturation region (conduction) or in the cut-off region (non-conduction), but it cannot work in the amplification region. This is relatively easy to understand. If it works in the amplification region, the Vce voltage is difficult to determine, which will result in an intermediate state when you want a high or low level.

What is the saturation state of a transistor? Assuming that the transistor is working in the amplification state, the amplification factor is β. If the base has Ib current flowing through it, then the collector Ic=β*Ib, and Ic will also produce a voltage drop Urc on Rc. So, Urc+Uce=Vcc. It can be inferred that the larger Ib is, the larger Urc=β*Ib*Rc is. When Ib is large enough, when Urc=Vcc, Uce=Vcc-Urc=0.

When the base current continues to increase, and the collector current no longer increases (tends to be stable), the transistor reaches saturation. When saturated, the collector junction of the transistor is forward biased, and the emitter junction is forward biased. This is what the textbooks say.

It is impossible for Uce to be less than 0 because if the voltage is reversed, the current will also be reversed, which is obviously not true.

The actual Uce will continue to remain close to 0. At this time, the actual current of Ic is less than β*Ib. At this time, the circuit can no longer meet the amplification factor of β. The transistor is no longer in the amplification state, but has entered the saturation state.

We just need to make the calculated Urc=β*Ib*Rc>Vcc, then the transistor will work in saturation state.

For example, in the common IO port of a single-chip microcomputer, in the transistor switch circuit design, the IO port has a certain load capacity. But the current is very small and the driving ability is limited, generally within 10-20mA, so it is necessary to design a transistor drive circuit, etc.

Now the question is, we invite you to answer the question based on your own knowledge and experience in actual circuit design. To encourage you to participate in the reply, you will be rewarded with core points.

If you have your own insights or actively analyze and solve problems, you will also get more core points~

Everyone is speaking enthusiastically, looking forward to your discussion~,,,,

Question 1: For example, when driving a buzzer or LED, should we use NPN or PNP? What are the reasons? How should we configure the drive resistance parameters in the circuit?

Question 2: As shown in the figure below, if the voltage is 5V, the buzzer operating current is 30mA, the transistor amplification factor is 100, and the PN junction voltage drop is 0.7V, how do you determine the value range of the base resistor R1? Is it an empirical value?

Question 3: Or share with us the pitfalls you encountered in designing transistor drive circuits?

Also, how do you think the questions in these posts should be answered?

Question: [ What is the working principle of this anti-saturation drive circuit? ]

Question: [ What is the state of the transistor collector when it is open circuited and the collector is relative to the ground ]

There should be a lot of discussion on transistor drive circuit design in the forum before. The relevant information and questions are as follows:

【Analysis of transistor drive circuit and level conversion】

[ Everyone, take a look at the working principle of this triode switch ]

[ Please ask a question about the drive circuit ]

[ What is the state of the transistor collector open collector to ground ]

[ What is the working principle of the PNP transistor, its working principle when acting as a switch and its base resistance? ]

[ Working principle of transistor as switching circuit ]

[ The big choice between NPN and PNP transistor driven relays ]

[ How should the output uo of this ]

[ Selection of transistor base resistor value ]

[ Problem with the connection of resistors between BE and transistors when used as switches. ]

lansebuluo

If the tube is working in the amplification area, it will heat up seriously. As a switch tube, it is especially taboo to use it in this way.

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