Regarding the switching function of the triode, what are the switching characteristics of the triode

In order to make the transistor work in the amplified state, a bias resistance and a collector resistance are set in the triode circuit, and the output voltage is obtained by dividing the voltage of two resistors, which is a fixed bias amplification circuit, and there is a partial bias amplification circuit. I've been studying lately, so I can only explain that, and there's a lot more to come. It's complicated.

The amplification effect of some transistors is not very obvious, such as C9013, especially the SMD ones. If the transistor is used for switching, the conditions that need to be met are VBC>0 and VBE>0. In this way, the switching effect can be realized, and the base control is generally controlled by a single-chip microcomputer or an optocoupler.

In this way, it is possible to change directly from the cut-off state to the saturated state. In this case, the switching effect of the transistor is revealed.

The function is to let the transistor work in the saturation state and the cut-off state, and the saturation state requires UB UC, so the amplitude of the base input pulse is either 0 or the amplitude of UC. In this way, the tube goes directly from the cut-off state to the saturated state, avoiding the amplification area and entering the switch working state.

The switching transistor has the characteristics of long life, safety and reliability, no mechanical wear, fast switching speed and small size. It is mainly used for the conversion of circuits off and on. Because it has the function of completing the circuit opening or switching, it is widely used in switching circuits.

The switching transistor uses a small current to control the on/off of a large current, and has a wide range of applications. Low-power switch tubes are used in power supply circuits, drive circuits, switching circuits, etc. The high-power tube can be used for switching power supplies for color TVs and communication equipment.

It can also be used for low-frequency power amplification circuit, current adjustment, etc., and high-back-voltage high-power switch can be used for color TV line output tube.

Switching triode: A triode that is mainly used for the conversion of circuits from turn on and off.

The transistor generally refers to the bipolar crystal triode, which is a current control device, when the saturation is on, the emitter is positively biased, the collector is reversed, and the FET is a voltage-controlled transistor, when the control voltage reaches a certain value, it will enter the saturation region from the resistance region, generally the gate reaches about 15V (MOSFET), and the gate voltage of the saturation conduction is different due to the different structures

The design principle is to let the transistor work in the saturated state and the cut-off state, the saturation state requires UB uc, so the amplitude of the base input pulse is either 0 or the amplitude of the uc, so that the tube will go directly from the cut-off state to the saturated state, avoiding the amplification area, and entering the switch working state, and it is useless to be verbose.

When the transistor is in the amplified state, it can neither be saturated nor cut-off, so it is necessary to reasonably select the bias current and collector resistance, and often use a negative feedback bias circuit. When a triode is used in a switching circuit, the bias current is either 0 or larger, saturating the transistor. Take the common emitter circuit as an example, the emitter can not be connected to the resistor, the base resistance collector resistance is less than the current amplification of the transistor, and the general base resistance is about 10 times that of the collector resistance.

The tube works in the saturation cut-off state for 2 states.

3 transistors when making switches. The base + saturation current positively biases the collector joint. At this time, the tube is in a saturated state, and the CE resistance is very small. Quite with on. When it is necessary to shut down, the base current is removed, and the tube is cut off, and it is quite disconnected at this time.

If the transistor is regarded as a switch, if the switch is on, the base voltage is higher than the emitter, and if the base voltage is lower than the emitter voltage, the switch is disconnected;

The transistor works in a saturated or cut-off state, so as to achieve a switching effect.

Fig. 5, simple switching triode circuit diagram Fig. 6, modified triode switching circuit - Darlington circuit diagram.

Simple transistor switch: The circuit is shown in Figure 5, the resistor RC is the resistor used for LED current limiting to prevent the voltage from too high and burning out the LED (light-emitting diode), adjust the input signal vin from 0 to the maximum (divided into about 20 intervals), observe and record the vout of the pair and the brightness of the LED. When the transistor switch is open, VOUT = VCC = 12 V and the LED is not lit.

When the transistor switches the path, vout = , the LED will light up. Modified transistor switching: Because the transistor needs to pass through the linear region from the cut-off zone to the saturation zone, there is no clear boundary between the switching effect.

In order to make the effect of the triode switch clear, two transistors can be connected in series, and the circuit is shown in Figure 6. Similarly, the input signal vin is adjusted from 0 to maximum (divided into about 20 equal intervals), and the corresponding vout and the brightness of the LED are observed and recorded. As can be seen from the above, almost any type of transistor can be used as an electronic switch, and can also be used to control heating equipment if conditions permit.

It can be seen that the switching triode is only a general concept, but there are a few special switching transistors on the market**.

Animated image to explain the working principle of the transistor.

According to the understanding of the figure, the transistor does not work in the switching state, but in the amplification state, so as to adjust the brightness of the light-emitting tube in different bins. If it is working in the switching state, it can only be on and off and 1 and 0. The fixed brightness is determined by the current limiting resistor adjustment of the light-emitting tube in series.

When using one transistor, the light-emitting tube is bright when saturated, and when using two triodes, the first saturated and the second cut-off light-emitting tube is not bright.