Figure \(\PageIndex{4}\): Transfer characteristic. Rectifier Efficiency Rectifier efficiency is defined as the ratio of DC output power to the input power from the AC supply. Precision half-wave rectifier using NE5535 This circuit provides the right half-wave rectification of the input signal. For very long discharge times, large capacitors must be used. In a precision rectifier circuit using opamp, the voltage drop across the diode is compensated by the opamp. These stretched pulses are then fed to a comparator, which drives an LED. The combination of the positive and negative input swings creates an inverted, half-wave rectified output signal, as shown in Figure \(\PageIndex{16}\). \(C\) starts to discharge, but the discharge time constant will be much longer than the charge time constant. Thévenin Equivalent Circuit and Maximum Power Transfer, 11. This can be configured for either positive or negative peaks. The precision rectifier, also known as a super diode, is a configuration obtained with one or more operational amplifiers in order to have a circuit behave like an ideal diode and rectifier. The inverting op-amp circuit can be converted into an “ideal” (linear precision) half-wave rectifier by adding two diodes as shown in figure 2. If FET input devices are used, the effective discharge resistance can be very high, thus lowering the requirement for \(C\). Rectification never occurs because the diode requires 0.6 to 0.7 V to turn on. FIGURE 7: Op Amp Half-Wave Rectifier. This voltage is presented to the second op amp that serves as a buffer for the final load. As we can see from the figure 6 the circuit shown on figure 4 is indeed a full wave rectifier where diode threshold voltages are NOT causing any affects as it is case in diode rectifiers. The LF412 is a dual-package version of the LF411. First, note that the circuit is based on an inverting voltage amplifier, with the diodes \(D_1\) and \(D_2\) added. The op amp and circuit output waveforms are shown in Figure \(\PageIndex{5}\). In order to create the circuit output waveform, the op amp creates an entirely different waveform at its output pin. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. It consists of following sections: Precision half-wave rectifier; Inverting summing amplifier This output voltage is perhaps not too useful for meter calibration, but adding one opamp and a few precision resistors will give you 10 volts RMS which is a whole lot better. In this way, the inherent speed limitations of the op amp are shown, and effects such as those presented in Figure \(\PageIndex{6}\) may be noted. Measuring a Loudspeaker Impedance Profile, 17. Assuming that the LED forward drop is about 2.5 V, the 500 \(\Omega\) resistor limits the output current to, \[ I_{LED} = \frac{V_{sat} − V_{LED}}{500} \notag \], \[ I_{LED} = \frac{13 V−2.5 V}{500} \notag \], \[ I_{LED} = \frac{10.5 V}{500} \notag \]. This is a snapshot of the amplifier simulation (5 V voltage source on the right, LM324 op-amps): When its output is rising, the capacitor, \(C\), is being charged. Legal. Because FET input devices are used, their impedance is high enough to ignore. As an example, if C is 10 \(\mu\)F, and the maximum output current of the op amp is 25 mA. If any of the resulting pulses are greater than 5 V, the comparator trips, and lights the LED. 5. \[ T = 10 M \Omega \times 10 nF \notag \], The 10 nF capacitor is small enough to maintain a reasonable slew rate. Because the feedback signal is derived after the diode, the compensation is as close as the available loop gain allows. Try to change OUT1 DC offset and amplitude and observe results. Precision Rectifiers, Absolute value circuits, 22. The output will be at the virtual ground potential ( - input terminal ) through the 10kΩ resistor. These peaks can cause havoc in other pieces of equipment down the line. This condition will persist until the input signal goes positive again, at which point the error signal becomes positive, forward-biasing the diode and allowing load current to flow. Its major drawback is a somewhat limited input impedance. What happens if the direction of the diodes is reversed? Actually it alters completely and hence t… The below shown circuit is the precision full wave rectifier. Due to the capacitor voltage, the diode ends up in reverse-bias, thus opening the drive to \(C\). Figure \(\PageIndex{5}\): Output of op amp. Larger capacitors will, of course, produce a lengthening of the charge time (i.e., the rise time will suffer). This time is determined by the device's slew rate. This might be as simple as a single RC network. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Precision Rectifier The ordinary diodes cannot rectify voltages below the cut-in-voltage of the diode. NI Multisim Live lets you create, share, collaborate, and discover circuits and electronics online with SPICE simulation included During its journey in the formation of wave, we can observe that the wave goes in positive and negative directions. An example application of an op amp-based rectifier is shown in Figure \(\PageIndex{18}\). The input pulses are expanded, so the LED will remain on for longer periods. Full wave Rectifier. No matter what the input polarity is, the output is always positive. For the positive half of the input, diode D1 is forward biased, closing the feedback around the amplifier. Also we can see that DC offset value is not excluded from the rectifying process making this circuit a absolute value circuit.The name absolute value circuit comes from the fact that, as we can see from the figure 6, the output signal (IN2) is an absolute value of the input signal (IN1). Circuit designers have two standard methods for designing a precision rectifier. This is an interesting variation, because it uses a single supply opamp but still gives full-wave rectification, with both input and output earth (ground) referenced. In order to track this, the op amp must climb out of negative saturation first. PRECISION RECTIFIER CIRCUITS The Figure 1 rectifier circuit has a rather limited frequency response, and may produce a slight negative output signal if D1 has poor reverse resistance characteristics. The precision rectifier is another rectifier that converts AC to DC, but in a precision rectifier we use an op-amp to compensate for the voltage drop across the diode, that is why we are not losing the 0.6V or 0.7V voltage drop across the diode, also the circuit can be constructed to have some gain at the output of the amplifier as well. Probably the first thing that pops into your head is the use of a diode, as in Figure \(\PageIndex{1}\). Even though the LED does light at the peak, it remains on for such a short time that humans won't notice it. As \(D_2\) is inside the feedback loop, its forward drop is compensated for. In the circuit uses NE5535 as main. You may wish to verify this as an exercise. MOS transistor common source amplifier, 2x small signal diodes (1N914 or similar), Build the circuit from figure 1 on the breadboard, Start the Oscilloscope & Signal generator application. When its output is rising, the capacitor, \(C\), is being charged. If the discharge time constant is much longer than the input period, the circuit output will be a DC value equal to the peak value of the input. Large capacitors can also degrade slewing performance. In this tutorials we use the terminology taken from the user manual when referring to the connections to the Red Pitaya STEMlab board hardware. The big advantage of this circuit is represented by the small threshold voltage and linearity. © Copyright 2017, Red Pitaya d.d. Not only that, the circuit of Figure \(\PageIndex{1}\) exhibits vastly different impedances to the driving source. Have questions or comments? Build the circuit from figure 4 on the breadboard. A circuit which can act as an ideal diode or precision signal – processing rectifier circuit for rectifying voltages which are below the level of cut-in voltage of the diode can be designed by placing the diode in the feedback loop of an op-amp. Current-mode circuits have always been a better choice for accuracy and high frequency performances. An alternating current has the property to change its state continuously. The output waveform consists of just the positive portions of the input signal, as shown in Figure \(\PageIndex{3}\). In summary, then, the input pulses are stretched by the peak detector. The result would be a distorted signal as shown in Figure \(\PageIndex{6}\). Along with the decrease of loop gain at higher frequencies, slew rate determines how accurate the rectification will be. The comparator trip point is set by the 10 k\(\Omega\)/5 k\(\Omega\) voltage divider at 5 V. When the input signal rises above 5 V, the comparator output goes high. If the input signal is negative, the op amp will try to source current. The output waveform is also shown in Figure \(\PageIndex{8}\). Normally, FET input devices are used, so from a practical standpoint, \(R\) sets the discharge rate. This precision rectifier operates from an asymmetrical supply, handles input signals up to 3 Vpp and has a frequency range that extends from DC to about 2 kHz. But, what happens if the input signal is only 0.5 V peak? The LF412 should be able to deliver this current. Figure \(\PageIndex{14}\): Precision full-wave rectifier. The BJT transistor connected as a diode, 23. Figure \(\PageIndex{17}\): Combination of signals produces output. The capacitor will continue to discharge toward zero until the input signal rises enough to overtake it again. This circuit can be used on its own as a half-wave rectifier if need be. One variation on the basic half-wave rectifier is the peak detector. A simple precision rectifier circuit. Also, the design was having lower packaging density. A Multisim simulation of the circuit shown in Figure \(\PageIndex{2}\) is presented in Figure 7.8. The circuit of Figure \(\PageIndex{11}\) uses a peak detector to stretch out the positive pulses. The fault stage can then light a warning LED, or in severe cases, trip system shutdown circuitry to prevent damage to other components. Even if a germanium device is used with a forward drop of 0.3 V, a sizable portion of the signal will be lost. channel and using vertical +/- controls, Set t/div value to 2ms/div (You can set t/div using horizontal +/- controls). One item to note about Figure \(\PageIndex{5}\) is the amount of time it takes for the op amp to swing in and out of negative saturation. When the input signal starts to swing back toward ground, the output of the first op amp starts to drop along with it. One of the items noted in Chapter 3 about negative feedback was the fact that it tended to compensate for errors. In order to produce a negative full-wave rectifier, simply reverse the polarity of \(D_1\) and \(D_2\). On the other hand, when the input is negative, the diode is reverse-biased, opening up the feedback loop. This is understood by observing the sine wave by which an alternating current is indicated. Even if the signal is large enough to avoid the forward voltage drop difficulty, the source impedance must be relatively low. Rectifiers, or ‘absolute-value’ circuits are often used as detectors to convert the amplitudes of AC signals to DC values to be more easily measured. In order to compare long-term averages, the input and scaled output signals are precision full-wave rectified and then passed through a peak-detecting or averaging stage. At this point the op amp's noninverting input will see a large negative potential relative to the inverting input. It can also be thought of as an analog pulse stretcher. Figure 6: Precision full-wave rectifier measurements - Absolute value circuit. Suppose that the op amp is in negative saturation and that a quick positive input pulse occurs. This example utilizes the 741 op amp model examined earlier. The discharge resistance is a function of \(R\), the impedance looking into the noninverting input of op amp 2, and the impedance looking into the inverting input of op amp 1, all in parallel. The precision rectifier converts AC signal to DC. The circuit shown in figure 4 is an absolute value circuit, often called a precision full-wave rectifier. The peak of the rectified output should now equal to the peak value of the input (only AC peak, note that DC level of the input signal is not transfered to the output). Sketch … The MOS transistor connected as a diode, 27. This is one of two signals applied to the summer configured around op amp 2. In order to accurately rectify fast moving signals, op amps with high \(f_{unity}\) and slew rate are required. Figure \(\PageIndex{2}\): Precision half-wave rectifier. One way of achieving this design is to combine the outputs of negative and positive half-wave circuits with a differential amplifier. To a first approximation, when the input is positive, the diode is forward-biased. This being the case, it should be possible to reduce the diode's forward voltage drop by a very large factor by placing it inside of a feedback loop. It should operate like a full wave rectifier circuit constructed with ideal diodes ( the voltage across the diode, in forward conduction, equals 0 volts). For the negative half of the input diode D1 is reverse biased and diode D2 is forward biased and the circuit operates as a conventional inverter with a gain of -1. Given an op-amp configured with negative feedback, the inverting and non-inverting input terminals will try to reach the same voltage level, often referred to as a “virtual ground. Extension connector pins used for -3.3V and +3.3V voltage supply are show in the documentation here. We can modify the half wave rectifier to make full wave rectifier or absolute value circuit. The basic problem when trying to visually monitor a signal for overloads is that the overloading peak may come and go faster than the human eye can detect it. Figure \(\PageIndex{18}\): Power amplifier overload detector. The one problem with this is that only positive peaks are detected. It is Dual High Slew Rate Op-Amp. If the aforementioned pulse is only 20 \(\mu\)s wide, the circuit doesn't have enough time to produce the pulse. Precision Rectifier Circuit for CT Signal Conditioning 144 Applications H 3500 Scarlet Oak Blvd. If only slow signals are to be rectified, it is possible to configure the circuit with moderate gain if needed, as a cost-saving measure. The precision rectifier, also known as a super diode, is a configuration obtained with an operational amplifier in order to have a circuit behave like an ideal diode and rectifier. [ "article:topic", "license:ccbyncsa", "showtoc:no", "authorname:jmfiore" ], https://eng.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Feng.libretexts.org%2FBookshelves%2FElectrical_Engineering%2FElectronics%2FMap%253A_Operational_Amplifiers_and_Linear_Integrated_Circuits_-_Theory_and_Application_(Fiore)%2F07%253A_Nonlinear_Circuits%2F7.02%253A_Precision_Rectifiers, Professor (Electrical Engineering Technology). A circuit which can act as an ideal diode or precision signal–processing rectifier circuit for rectifying voltages which are below the level of cut-in voltage of the diode can be designed by placing the diode in the feedback loop of an op-amp. (b) Figure 2(b) shows a precision rectifier circuit. The LED needs to remain on for longer periods. If large negative peaks exist, they will not cause the LED to light. Each circuit taken separately in a simulator works fine, but as soon as I combine the two everything breaks down. Verified Designs offer the theory, component selection, simulation, complete PCB schematic & layout, bill of materials, and Another way to accomplish this is to utilize a full-wave rectifier/detector. Let's start the analysis with this portion. Because the diode remains reverse-biased, the circuit output stays at 0 V. The op amp is no longer able to drive the load. This is no different than the case presented with compensation capacitors back in Chapter Five. The discharge time constant is set by \(R\) and \(C\). For a full wave rectifier, it is given by the expression, r = 1⁄4√3. Single-Supply Low-Input Voltage Optimized Precision Full-Wave Rectifier Reference Design TI Designs – Precision Circuit Description TI Designs – Precision are analog solutions created by TI’s analog experts. The output impedance of the first op amp is low, so the charge time constant is very fast, and thus the signal across \(C\) is very close to the input signal. In the previous works on DDCC[7] with CMOS (350nm), the circuits suffer from the problem of leakage current. Another way is shown in Figure \(\PageIndex{14}\). For designs in which a high degree of precision is needed, op-amps can be used in conjunction with diodes to build precision rectifiers. For positive input signals, the input current will attempt to flow through \(R_f\), to create an inverted output signal with a gain of \(R_f/R_i\). These signals are then compared by the fault stage. Negative feedback tends to reduce errors by an amount equal to the loop gain. This is more convenient than the basic rectifiers, since this circuit is able to rectify signals smaller than the diode threshold voltage. The output of the op amp is also shown so that the effects of negative feedback illustrated in \(\PageIndex{5}\) are clearly visible. Precision Full-Wave Rectifier, Dual-Supply TI Precision Designs Circuit Description TI Precision Designs are analog solutions created by TI’s analog experts. This would also be the case if an improperly functioning power amplifier produced a DC offset. Explain how it works and determine the point at which the LED lights. As we have seen in the simple rectifier circuits constructed with diodes, the circuit does not respond well to signals with a magnitude less than a diode-drop (0.7V for silicon diodes). Precision Rectifier Circuits Rectifier circuits are used in the design of power supply circuits. It has an output of 7.071 volts RMS (±0.1%) over a programmable frequency range of 10 Hz to 100 KHz. This turns \(D_1\) on, creating a path for current flow. Note the accuracy of the rectification. Diode D2 is reverse biased disconnecting the output from the amplifier. FIGURE 8: Circuit Behavior on Low Frequency. The name, full-wave rectifier, is a special case application where the input … When the input signal swings negative, the op amp tries to sink current in response. Repeat experiment with the direction of one diode (D1) reversed. The purpose of this experiment is to investigate precision rectifiers or absolute value circuits. St. Louis MO USA 63122 V: 636-343-8518 F: 636-343-5119 Figure \(\PageIndex{12}\): Waveforms for the circuit of Figure \(\PageIndex{11}\). It is useful for high-precision signal processing. A full-wave rectifier has the input/output characteristic shown in Figure \(\PageIndex{13}\). The output of a peak detector can be used for instrumentation or measurement applications. On the left bottom of the screen be sure that IN1 and IN2 V/div are set to 200mV/div (You can set V/div by selecting the desired At first glance it seems as though it is impossible to rectify a small AC signal with any hope of accuracy. In essence, the circuit reduces to a simple voltage follower with a high input impedance and a voltage gain of one, so the output looks just like the input. The design of a precision full-wave rectifier is a little more involved than the single-polarity types. Thus, positive input signals are amplified and inverted as in a normal inverting amplifier. If the discharge time constant is somewhat shorter, it has the effect of lengthening the pulse time. The circuit works as follows: If v I … The op amp's output polarity also forces \(D_2\) off, leaving the circuit output at an approximate ground. Moreover, in an integrated circuit (IC), the modularity of sub-circuit is preferred, especially for the ease of fabrication. Figure \(\PageIndex{10}\): Effect of \(\tau\) on pulse shape. Figure \(\PageIndex{1}\): Passive rectifier. This is a very slow slew rate! Watch the recordings here on Youtube! For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Because the inverting input is at virtual ground, the output voltage of the op amp is limited to the 0.6 to 0.7 V drop of \(D_1\). Plan some tests to see if this circuit indeed is a rectifying circuit. Figure \(\PageIndex{7}\): Rectifier with gain. Revision 33755bb0. Imagine for a moment that you would like to half-wave rectify the output of an oscillator. The precision rectifier is a type of rectifier that converts the AC signal to DC without any loss of signal voltage. The circuit is shown redrawn with the nodes labeled. For positive portions of the input, the op amp must produce a signal that is approximately 0.6 to 0.7 V greater than the final circuit output. Due to the effect of negative feedback, even small signals may be properly rectified. An example input/output wave is shown in Figure \(\PageIndex{12}\). It should operate like a full wave rectifier circuit constructed with ideal diodes (the voltage across the diode, in forward conduction, equals 0 volts). This is shown in Figure \(\PageIndex{7}\). This extra signal effectively compensates for the diode's forward drop. A positive peak detector is used along with a simple comparator in Figure \(\PageIndex{11}\) to monitor input levels and warn of possible overload. Study the circuit and determine how it works. The other input to the summer is the main circuit's input signal. The proposed full-wave rectifier circuit shows better precision. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Unfortunately, a simple scaled comparison of the input and output signals of the power amplifier may be misleading. Precision Rectifier Circuit. In such applications, the voltage being rectified are usually much greater than the diode voltage drop, rendering the exact value of the diode drop unimportant to the proper operation of the rectifier. (Normally, gain is set to unity.) This voltage is presented to the second op amp that serves as a buffer for the final load. As shown, the diode passes positive half waves and blocks negative half-waves. The circuit diagram of a full wave rectifier is shown in the following figure − The above circuit diagram consists of two op-amps, two diodes, D 1 & D 2 and five resistors, R 1 to R 5. Repeat experiment with the direction of both diodes reversed. This is shown in Figure \(\PageIndex{2}\), and is called a precision half-wave rectifier. Because this circuit utilizes an accurate op amp model, it is very instructive to rerun the simulation for higher input frequencies. In a Diode voltage drop is around 0.6V or 0.7V. From the waveform menu select SINE, deselect SHOW and select enable. The actual diodes used in the circuit will have a … Figure \(\PageIndex{8a}\): Precision rectifier simulation schematic. At low frequencies where the loop gain is high, the compensation is almost exact, producing a near perfect copy of positive signals. Figure 1: Connection diagram for precision half-wave rectifier, Figure 3: Precision half-wave rectifier measurements. The precision rectifier of circuit \(\PageIndex{14}\) is convenient in that it only requires two op amps and that all resistors (save one) are the same value. The SWR300 is a precision sinewave reference IC from Thaler Corporation. I am trying to use a first non-inverting amplifier stage, followed by a precision half-wave rectifier. A full wave rectifier produces positive half cycles at the output for both half cycles of the input. Basic circuit. For long discharge times, high quality capacitors must be used, as their internal leakage will place the upper limit on discharge resistance. Current Sensing using a Difference Amplifier, 18. Even with ideal rectifiers with no losses, the efficiency is less than 100% because some of the output power is The resulting transfer characteristic is presented in Figure \(\PageIndex{4}\). This circuit has limitations. The voltage at point A in Figure \(\PageIndex{14}\) is the output of the half-wave rectifier as shown in Figure \(\PageIndex{16}\). Precision rectifier circuits combine diodes and operational amplifiers to eliminate the effects of diode voltage drops and enable high-accuracy, small-signal rectification. No signal current is allowed to the load, so the output voltage is zero. This circuit is comprised of two parts: an inverting half-wave rectifier and a weighted summing amplifier. Figure \(\PageIndex{6}\): High frequency errors. If there is a substantial difference between the two signals, the amplifier is most likely clipping the signal considerably or producing an unwanted DC offset. If the positive pulse were a bit longer, say 50 \(\mu\)s, the op amp would be able to track a portion of it. The resulting negative error signal forces the op amp's output to go to negative saturation. Here is how it works: The first portion of the circuit is a precision positive half-wave rectifier. Impedance Measurement - Frequency Effects, 12. The -3.3V and +3.3V voltage supply pins do not have short circuit handling and they can be damaged in case of short circuit. The precision rectifier or super diode is an arrangement achieved with one or more op-amps (operational amplifiers) in order to have a circuit perform like a rectifier and an ideal diode. Finally, for negative half-wave output, the only modification required is the reversal of the diode. Missed the LibreFest? Figure \(\PageIndex{11}\): Detector for Example \(\PageIndex{1}\). Determine the voltage gain on the positive-going and the negative-going half cycles. These two signals will combine as shown in Figure \(\PageIndex{17}\) to create a positive full-wave output. Mathematically, \[ V_{out} =−K \sin \omega t+2 K \sin \omega t \notag \]. This limits their use in designs where small amplitudes are to be measured. Oscilloscope & Signal generator application is used for generating and observing signals on the circuit. This sort of result is quite possible in the communications industry, where the output of a radio station's microphone will produce very dynamic waves with a great many peaks. Perform these tests, fully documenting all tests and results in your lab report. It is possible to use a similar circuit to detect negative peaks and use that output to drive a common LED along with the positive peak detector. Using a 741 op amp with \(\pm\)15 V supplies, it will take about 26 \(\mu\)s to go from negative saturation (-13 V) to zero. It also has the effect of producing the overall contour, or envelope, of complex signals, so it is sometimes called an envelope detector. Figure \(\PageIndex{13}\): Transfer characteristic for fullwave rectification. The actual diodes used in the circuit will have a forward voltage of around 0.6 V. Before connecting the circuit to the STEMlab -3.3V and +3.3V pins double check your circuit. There is a very fundamental concept that should help in understanding how this circuit operates. Precision rectifier (a) What is the disadvantage of the precision rectifier circuit in Figure 2(a)? This circuit will produce an output that is equal to the peak value of the input signal. Figure 4: Precision half-wave rectifier with DC smoothing filter. As it does so, the diode becomes reverse-biased, and current flow is halted. In maintaining the modularity, an attempt is made to design a precision rectifier, needed for demodulator, as an extension of the proposed modulator with little modifications. The Comparator, Positive Feedback and Schmitt Trigger, 21. In a precision rectifier circuit using opamp, the voltage drop across the diode is compensated by the opamp. It raises in its positive direction goes to a peak positive value, reduces from there to normal and again goes to negative portion and reaches the negative peak and again gets back to normal and goes on. A new precision peak detector/full-wave rectifier of input sinusoidal signals, based on usage of dual-output current conveyors, is presented in this paper. There is also a sharp transition as the input crosses zero. Possible output signals are shown in Figure \(\PageIndex{10}\). From the measurements shown on picture 3 we can observe following: Here is how it works: The first portion of the circuit is a precision positive half-wave rectifier. Another Precision Rectifier (Intersil) A simple precision rectifier circuit was published by Intersil [ 2 ]. Figure \(\PageIndex{16}\): Output of half-wave rectifier. f is the mains supply frequency 50 Hz. 18.9.1 Precision Half-Wave Rectifier: The “Superdiode” Figure 18.35(a) shows a precision half-wave-rectifier circuit consisting of a diode placed in the negative-feedback path of an op amp, with R being the rectifier load resistance. On the plus side, because the circuit is non-saturating, it may prove to be faster than the half-wave rectifier first discussed. In this way, the op amp does not saturate; rather, it delivers the current required to satisfy the source demand. Rectification never occurs because the op amp is no different than the basic rectifiers, since this circuit will an. 1 } \ ): rectifier with gain need be 7 ] with CMOS ( 350nm ), as... Set to unity. not only that, the compensation is almost exact, producing a near perfect of! Led does light at the output voltage is presented in figure \ ( C\ ) their use Designs! 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