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3.7.4. Clippers
Another interesting application of diode clipper is <voltage limiter. In a Shearing circuit, the output voltage is limited at some level n and prevented to grow beyond a certain positive or negative value. A clipped voltage can be used as a digital pulse to digital circuits or computer.
The circuit of figure 3.7.11 is a positive clipper circuit and limits the output voltage to a value below a certain level eg below 5,7 V ^ v
Va = 5 V.
Suppose the input source voltage is V. Date = 15 (vi) and the voltage value VA is 5V. During the positive half period (0 <t <T / 2), the output voltage follows the input voltage because there is no current in the circuit (after the diode does not conduct) until the input voltage is V. > 5,7 V. Then circulating current in the circuit and are:
Example 3.7.3
For a full figure 3.7.5 rectifier filter capacitor, the maximum input voltage is Vm = 24 V. The load voltage must have average Vdc = 18 V and the DC load current Idc = 500 mA. If the frequency of the grid voltage is f = 50 Hz, to determine the required capacitor for satisfactory smoothing the output voltage.
Figure 3.7.11.
Positive clipper circuit
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3.7.12
In figures 3.7.12 shows the input and output voltages.
Figure 3.7.13 gives the negative clipper circuit and the input and output voltages. During the positive half-voltage diode does not conduct and the output voltage equals the input voltage. During the negative half period, the voltage is limited to a value: VL> - VB.
Vi, V.
Figures 3.7.12
Input voltages and output (red) positive clipper.
Figure 3.7.13.
Negative clipper. (A) Circuit (b) input and output waveforms
By combining the above two circuits, as shown in Figure 3.7.14, created a double clipper.
O double clipper can be done with Zener diode 2 connected as in Figure 3.7.15.
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Figure 3.7.14.
Double with shared clipper diodes (a) Circuit (b) Output Waveform
Figure 3.7.15. Double clipper with Zener. (A) Circuit, (b) Output Waveform
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Example 3.7.4
In the shape kykioma 3.7.15 The maximum value of input voltage is Vm = 15 Zener diodes n.Oi have the same voltage VZ = 10 V. Given R = 10 KO. To design the output voltage VL.
Solution
We examine the following cases: 0 <Vi <10V: Then Z1 Zener diode conducts it is properly polarized, while the Zener diode Z2 does not conduct because it has reached the breakdown voltage. So VL = V..
10 <V. <15V: Then VZ2 = 10V, VZ1 = 0,7 V. So VL = 10,7 V.
-10 <V. <0: Then by analogy with the first case of VL = V..
-15 <V. <-10: It applies VZ1 =-10V, VZ2 = -0,7 V. So
VL = -10,7 V. The output shown in Figure 3.7.16
Figure 3.7.16 Example Output
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3.7.5. Voltage doubler
In some applications, such as the oscilloscope to a computer screen, the electrical power needs are small but rising voltage circuit 2, 3 or more times. The circuits that lift, so multiply, voltage multipliers are called voltage if the voltage doubles the voltage doubler circuit is called. Figure 3.7.17 shows a voltage doubler and the resulting output waveform VL.
Figure 3.7.17 Voltage Doubler (a) Circuit, (b) Waveforms
During the negative half-polarized diode D1 correctly, while D2 is reverse polarized. O capacitor C1 is charged with the maximum input voltage Vm. During the negative half period, the diode D2 is conducting while D1 is reverse biased. The capacitors C1 and C2 are connected in series and loaded so that:
VC! + VC2 = Vm 3.7.13
The load on already overloaded capacitor C1 is transferred to capacitor C2 and therefore:
Vc2 = 2Vm 3.7.14
The voltage of the capacitor C2 is applied and the edges of the load resistance. If the load resistor RL is a great honor, then the decay time constant of the capacitor is large so that the output voltage is constant and twice the input voltage.
Besides the voltage Doubler, a triple, quadruple or siastis-voltage multiplier, but the circuits will address the Second and Third year.
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