LONG LIFE BATTERY-In an on-off circuit, a photovoltaic cell
In an on-off circuit, a photovoltaic cell
In an on-off circuit, a photovoltaic cell connected in series in the base circuit of a transistor can achieve very good results.Figs. 2 - 22 show the use of a solar cell in the base circuit of an npn transistor.As long as the solar cell is not irradiated by strong light, there is no current passing between the base and emitter, and therefore there is no conduction between the collector and emitter.But when light hits the battery, it generates current through the collector-emitter and the load.In this case, the load may be the coil of a relay which is connected to a simple incandescent lamp circuit.After the relay operates, its contacts close and turn on the incandescent lamp circuit, as shown in fig. 2 - 22, which connects the solar cell to the base circuit of the n - p - n transistor, as shown in fig. 2 - 23, the photo-controlled switch circuit Yan 2 - 23 consisting of the solar cell, the product tube and the relay.This is a circuit that uses sunlight to control the operation of a certain device.If it is required to be able to switch on the circuit in the absence of sunlight, simply replace a relay with normally open contacts with a relay with normally closed contacts.The relay with normally closed contacts keeps its normally closed contacts closed when no current passes through the relay coil, so the incandescent lamp circuit is turned on.On beer, when no sunlight hits the surface of the solar cell, the transistor does not conduct, no current flows through the relay, and the relay does not operate, so the lighting circuit is always on at night.When the sun rises the next morning, the light irradiates the surface of the solar cell, turning on the transistor to supply power to the relay coil, and the relay opens the normally closed contact, cutting off the light circuit.Zirconia is: When the sun rises, it can automatically cut off the lighting circuit.This is the automatic lighting of most daytime lights and night lights?The basic circuit of the switch, any circuit that can be controlled by a variable resistor, can basically be controlled by a photoelectric conduit.This means that people can control the circuit with light intensity, and any circuit that can be controlled with weak current can be controlled with a solar cell through the intensity of light.
Many people often misinterpret that solar electronic circuits are powered by light energy, but this is not the case.In many designs, a conventional power supply is used, and light changes are used to control the 2 - 6 phototransistor
Built - in photosensitive element
Photosensitive electric bladder is an electronic component composed of two types of semiconductor materials tightly packed together.This kind of electronic component has a characteristic that deserves our attention, that is, when light irradiates the junction, electrons flow.If this junction, which can be transmitted by some kind of radiation light, is fixed on another semi + conductor layer called collector, then the light guiding current generated by the junction of the photosensitive element is amplified as in a transistor.The sensitizing region is like the base of a transistor. When light irradiates this region, it generates an input signal, which is very similar to a combined circuit composed of a photosensitive electrical sister and a P - N - P transistor.The connection mode of this circuit is shown in figs. 2 - 24.In fact, the phototransistor encapsulates the photoresistor or photodiode in a unit instead of a separate photoresistor or photodiode.
As mentioned above, phototransistor is actually a combination of phototransistor and transistor in -?The reader may wonder why the circuits of discrete components ( transistors, resistors, photoelectric elements ) are still widely used.The main reason for this is that the production of E: before @ photosensitive triode is limited, and the application of series transistors can adapt to more circuit designs.At the same time, according to the actual situation of readers, the electronic equivalent circuit of ordinary transistor and low-cost photo - transistor 2 - 24 is adopted
Resistors are easier to do than buy phototransistors.Although the price of a certain phototransistor produced by some manufacturers can be close to or lower than the total price of discrete components, it can only be suitable for a single purpose and can not be widely used in various solid-state circuits. It can only work in circuits designed according to its operating parameters.Of course, if you can buy a suitable phototransistor in your region, it is very good.However, in a short period of time, it may not be possible to buy suitable devices. In this case, it is also very convenient to use ordinary transistors and small photoelectric elements for assembly.
In some applications, phototransistor is a very suitable device. The switch control mentioned above is a good example, but one prerequisite is that the light intensity of the light source must remain unchanged.It is not ideal when photoelectric devices have to rely on sunlight to turn on or off a circuit.Figs. 2 - 25 show a day-and-night on-off circuit discussed above. as can be seen from the figure, there is an additional element in the circuit, which is a variable resistor or a potentiometer, to regulate the current generated by the photovoltaic cell to control the conduction of the transistor.If this element is not connected in series, sometimes the lighting may go out prematurely, but after the variable resistor is connected in series, the substrate current can be limited, that is, the conduction of the transistor must wait until the base current increases to the starting value: the lighting will not be put out prematurely.In this way, the control loop cannot use the phototransistor, because the phototransistor's photo switch controlled by the variable resistor is shown in Figure 2 - 25.
The circuit between the photosensitive cell and the base of the transistor is integrated on a single crystal and enclosed in a housing.
If the opposite happens, it means that the lights are lit too early in the evening.The circuit shown in figs. 2 - 26 can be used to prevent this.It can be seen in the figure that a photo resistor and a variable resistor are serially connected into the base loop of the transistor.This control circuit can be adjusted. It can adjust the variable resistance according to the required illuminance, obtain a critical base current, and turn on the triode.The photoresistor determines the resistance value according to the required average illuminance of light in the circuit.If the resistance value is too large, the circuit can be appropriately modified, as shown in fig. 2 - 27, with an additional variable resistor in parallel with the photo resistor and variable resistor of fig. 2 - 27
The sensitive resistors are connected in parallel to control the internal resistance of the components, so that the circuit can achieve higher trigger sensitivity and wider adjustment range in function.
The purpose of this chapter's discussion on electronic devices such as transistors and phototransistors to discharge batteries is to make it clear that many kinds of electronic circuits can be obtained by combining the phototransistors with the existing common components.Many of the concepts described in this chapter will be directly applied to the circuit design described later, and many of the principles discussed will also be applied to the experimental circuits described below.The circuits described above all use relatively simple single-stage devices, which can be greatly improved or transformed to provide designs for more complex electronic circuits, sometimes even combining photovoltaic cells and photoresists in the base-emitter circuits of some transistor circuits.