Column: Circuit drill
Figure 3 shows an AC-DC converter
circuit with a more precise output. Its primary components are a pair of operational amplifiers. When 0-5Vdc is applied at its input, this circuit provides a wide DC ouput range.
Checking the circuit’s accuracy Here we will analyse this circuit’s accuracy, as well as if its output voltages correspond to that of the applied AC signal. In our experiment, we will gradually
increase the input signal from 1Vac to 10Vac in 1Vac increments, and its frequency will be varied from 1Hz to 100kHz in 10Hz steps. Te measured output DC voltages will then be plotted to discover the relationship between all the variables; see Figure 4. In addition, we assume the following:
• All circuit component values are kept unchanged.
• Te magnitude of the input signal ranges between 1Vac and 5Vac peak value. • Te ambient temperature is kept at 25o
C.
Monitored performance Figure 4 shows that the output DC signal is not linear over the entire input signal’s amplitude range. Te performance of the circuit may be broken down into four distinct zones, according to the rate of output DC voltage generation for each 1Vac fed at the input; see Table 1. For instance, when the input voltage is below 1Vac, the circuit will output 13mVdc for every 1Vac increment. When the input signal’s amplitude is between 1Vac and 2Vac, the circuit produces 4mVdc for every 1Vac. For input signals above 7Vac, the circuit
loses its ability to create a significant output voltage. Because the output span is so narrow, running our circuit in this zone will not be useful. It’s important to note that during this
experiment we changed the frequency of the input signal, proving that the circuit maintains a fairly stable output at 100kHz, in contrast to the magnitude of the input signal’s voltage.
Figure 3: Typical, precision, AC-DC converter circuit
Figure 4: The relationship between the input and output voltages
Table 1: Operating zones of our AC- DC converter
www.electronicsworld.co.uk June 2023 09
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