Shockley diode working and volt ampere characteristic gas jet compressor


If anode is made positive with respect to the cathode, junctions J 1 and J 3 get forward biased while junction J 2 gets reverse biased. Almost no voltage drop takes place across forward biased junction J 1 and J 3 and almost the complete applied voltage appears across the reverse biased junction J 2. natural gas in spanish The current that flows through the device is, therefore, the small reverse saturation current I O od junction J 2. This is the OFF state of the device. As the applied voltage is progressively increased, the current increased nominally. However, once the firing on breakdown voltage V BO is reached, the device fires and the current increases abruptly and the voltage drop across the device decreases sharply and the diode is now in the ON state. Thus, at breakdown point, the device switches from the OFF state or the blocking state to the ON state. Two-Transistor Version of Shockley Diode

The current-voltage characteristic may be studied on considering the diode to be formed of two transistor Q 1 and Q 2 placed back-to-back. Figure 2(a) shows the diode split up into two parts, displaced mechanically but connected electrically. The transistor Q 1 is a pnp transistor while Q 2 is a npn transistor. british gas jokes It may be seen that n-type base region of pnp transistor Q 1 forms the n-type collector of npn transistor Q 2 while the p-type collector of pnp transistor Q 1 forms the base of transistor Q 2. The junction J 2 thus forms the collector-to-base junction of both the transistors.

From equation (7), it is obvious that as the quantity approaches unity, current I increases very rapidly and ultimately the device breaks down. The factor responsible for this behavior is the regenerative manner in which the two constituent transistors Q 1 and Q 2 are interconnected. With appreciably less than unity, as per Equation (7), current I is extremely small and the pnpn diode acting as the switch is in the OFF state. However, with , the current is extremely large and the switch is said to be in the ON state. In this ON state, the total voltage drop across the pnpn diode becomes very small and current I is large, limited only by the external series resistance R.

The pnpn diode may exist in either of the two states namely the ON state or the OFF state. This is obvious from the following reasoning: For silicon device, for very low currents, are very small so that is also small resulting in the OFF state. For large currents, and are large so that equals unity, a condition necessary for ON state. As the applauded forward voltage across the diode is increased from zero, current starts increasing from zero. However, at the reverse biased junction J 2, the avalanche breakdown takes place causing increase in current. This increase in current results in corresponding increases in and . electricity wikipedia in hindi With increasing applied voltage V, and continually increase until the condition , is reached resulting in breakover. At the breakover point, we may expect both and to be close to unity individually. Then as per Equation (7), current I should reverse. But this does not happen because in the ON state, junction J 2 gets forward biased causing both the constituent transistor Q 1 and Q 2 to go into saturation causing the current gain to become small and restore the condition . Thus, two stable state OFF and ON are achieved. electricity in costa rica for travelers Voltage Drop in ON State of Shockley Diode

In the ON state, all the three junctions J 1, J 2 and J 3 are in forward biased condition. The total voltage drop across the pnpn diode almost equals the algebraic sum of voltage drops across these junctions. But the voltage drop across the middle junction J 2 is opposite to the voltage drop across junctions J 1 and J 3. Hence the net voltage drop across the pnpn diode equals (2 V BE,sat-V CB,sat) and is quite small (about 1.0 volt). Silicon and not Germanium to be used

With reverse Bias : With reverse bias, junctions J 1 and J 3 are reverse biased resulting in small reverse saturation current. With reverse bias equal to or greater than the avalanche breakdown voltage V RA, the breakdown takes place at these junction J 1 and J 3 are reverse current abruptly increases as shown in figure 4. This reverse bias operation of pnpn diode is of no utility.

With Forward Bias: With applied forward bias, extremely small forward current flows until the forward voltage equals the breakdown voltage V BO. The current is now I BO as shown in figure 4. On further increasing the forward voltage beyond V BO, the diode switches from the OFF (the blocked) state to ON (or saturation) state and then operates in the saturation region. gas urban dictionary The resulting current in the saturation region has slope corresponding to the external resistor R. The device is now said to latch signifying that the device will continue to remain in the ON state in spite of slight reduction in forward voltage and current. If the voltage is sufficiently reduced, the device switches to OFF state when the current has reduced to certain value I H, called the holding current or latching current. This current I H is the minimum current needed to hold the switch in its ON state. The corresponding voltage is called the holding voltage V H.

Table 1 gives for pnpn diode the typical values of voltage V BO, dynamic resistance for I B in the OFF region, current I H, voltage V H and dynamic resistance in the saturation region. This dynamic resistance in the saturation region decreases with the increase of current. Table 1: Typical Values of Characteristic Voltages and Currents in pnpn Diode

The operation of pnpn diode is somewhat temperature dependent. As the temperature decreases from room temperature 300k to 210k, there is negligible effect on V BO. electricity symbols and meanings But as the temperature rises to 370k, V BO decreases by about 10%. The holding current I H decreases appreciable with increase of temperature above room temperature but increases at a slow rate as the temperature decreases below the room temperature. Rate Effect

The breakover voltage V BO depends on the rate od increase of the applied voltage. Figure 5 gives the equivalent circuit of a pnpn diode in the OFF state. Here the 4 layer, 3 junction pnpn diode has been shown as a series combination of three pn junctions J 1, J 2 and J 3. In the OFF state, junction J 1and J 3 are forward biased while junction J 2 is reverse biased. Capacitance C across junction J 2 represents the transition capacitance of reverse biased junction J 2. An external voltage v in series with resistance R is connected across the pnpn diode. As the applied voltage v increases slowly, the current through the capacitance C may be neglected and the breakover takes place through the avalanche increases current through J 2 to reach the pint where the current gain and of constituent transistor satisfy the relation .

The same current flows through the junction J 1 and J 3. On the other hand, when the applied voltage v increases rapidly, the time rate of change of voltage v c is appreciable and appreciable current passes through the capacitor C. This current adds to the current in junctions J 1­ and J 3. k electric company duplicate bill Hence, the current now needed through the junction J 2to cause breakover gets reduced and the switching from OFF state to ON state takes place at a reduced voltage. The value of this transition capacitance C may be tens of pico-farads to over 100 pF. For such values of C, the value of of the order of tens of volts/µs may be adequate to cause noticeable reduction in switching voltage.