A simple amplifier circuit problem, a simple amplification circuit problem

Because relative to the AC signal, 12V is equivalent to a short circuit between 12V and the ground, RB is connected to the base at one end, and the other end is connected to 12V, which is also equivalent to grounding, because compared to the AC signal, 12V has been short-circuited to the ground, and 12V is the ground, so the RB in Figure B becomes parallel with the base-emitter. Why is a power supply equivalent to a short circuit for alternating current? Since this explanation is more troublesome, I won't say much here, but you can think of it this way, both ends of the power supply are generally connected with a large capacitor in parallel, because the capacitor is also equivalent to a short circuit relative to alternating current, which is equivalent to a wire, why?

For example, when the capacitor is charged with DC first, there is a charging current at the beginning, and there is no current after it is fully charged, which is equivalent to an open circuit, which means that the capacitor is not connected to DC.

But it's different for alternating current, because alternating current is sometimes positive and sometimes negative, and it changes over time. If the capacitor is connected to the alternating current, when the positive cycle of alternating current comes, charge the capacitor, when the negative cycle comes, discharge the capacitor and then charge it, and then discharge the capacitor and recharge it again in the positive cycle. Therefore, when drawing the AC path diagram, use wires instead of capacitors.

If you remove the capacitance and power supply from Figure A and change it to a wire, it will be the same as Figure B.

The difference between AC and DC, the most important point is that the power supply is short-circuited in the AC path. Of course, the capacitor is also short-circuited. With these two points understood, your problem is solved.

1. The essence of amplification in the amplification circuit is to amplify a weak current or voltage signal into a larger current or voltage signal. 2. The condition for the normal amplification of the amplifier circuit is that the amplifier must work in the amplification area, but not in the cut-off area and saturation area. 3. Feedback is to return the signal of the next level or several levels to the input stage, and this signal has the same polarity as the signal of the input stage, which is called positive feedback.

This signal is polarized opposite to the input-level signal and is called negative feedback. The result of the feedback can lead to some improvements in the performance of the amplifier. The amplification of the amplifier is increased, which is positive feedback.

Reducing the amplification of the amplifier is negative feedback. Negative feedback improves the output waveform by suppressing the output signal.

That's what it means, there are computers that can control the operation of the generator space shuttle where a given signal on the computer needs to be amplified by an amplification device to control the machine.

This equivalent circuit kills people.

There are no coupling capacitors, and neither are the power supplies.

People who will understand it at a glance, but people who will not look at it, question n multiple amplification circuits, if there is a coupling capacitor, the current can flow back from RL You pay attention to the C2, when the transistor is cut-off, the two poles of CE are quite open, that is, there is no transistor, the current passes through R2>C2>speaker" to the ground, such a circuit, to charge the capacitor.

When the transistor is turned on, the two poles of CE are quite short-circuited, then, the capacitor will begin to discharge at this time, and the current will pass through the + >C pole" E pole "Ground "Below the horn" capacitor -

So I understand.

If it is a dual power supply, the circuit can be changed, you can save the coupling capacitor, and then look at the so-called equivalent circuit, which has a hairy relationship with the actual circuit.

Yes, it should be downstream. The diagram is incorrectly marked.

3 The whole answer says that there is no forward bias voltage in the transmit junction, because the position of the base bias resistor in this circuit is drawn incorrectly. The base bias resistor RB should be connected between the base and ground, not between the base and the emitter (i.e., the positive power supply).

If it is connected between the base and emitter, then the transistor is always in the cut-off state.

The following diagram is correct.

1.Looking at the diagram below, the left represents the input of the amplifier and the right represents the output of the amplifier. VI is the input voltage and II is the input current.

2.If the input resistor RI is required, the output must be disconnected so that the voltage at the input can be divided by the current at the input.

Common emitter circuits.

Static work points are calculated using the conventional method.

The input and output resistors are directly set to the formula, remember to find the rbe.

The micro-equivalent circuit is drawn according to the learned circuit example.

The positive deviation of the emission junction and the reverse deviation of the collector junction are the basic conditions for the normal operation of the amplification circuit, and the positive deviation of the emission crust makes the base and the emitter conductive, and the base current flows into the emitter, because the inflow of the base current changes and reduces the potential barrier electric field of the collector junction, so that the collector has a penetrating current to flow through, and flows into the emitter through the base. The magnitude change of the base current changes the magnitude of the barrier electric field of the collector junction and also changes the magnitude of the collector current. Since the base current is less than the collector current b times, the large current is controlled by a small current, which plays a role in amplification.

The static operating point means that when the transistor has no signal input, the base has a certain current input, which corresponds to b times the collector current, and the base current flows into the emitter round. Due to the effect of the collector current, the transistor has a voltage UCE between the collector and the emitter, and the point corresponding to the UCE and IB or IC is the static operating point. The function of the static operating point is that when the signal is input, the transistor works in the amplification area, which effectively amplifies the signal.