Column: Circuit drill
The impact of battery voltage decline on oscillator performance
By Sulaiman Algharbi Alsayed, Managing Director, Smart PCB Solutions O
scillators convert direct current (DC) from a power supply to an alternating current (AC). Tese circuits are designed to generate
alternating signals at specific frequencies, and are very popular. Applications include timers, computer circuits, metal detectors, touch switches, radio circuits and a lot more – most electronic systems have at least one. Tere are many types of oscillators,
categorised around different principles. One popular type uses the famous 555 timer IC. Tis circuit fits in the “RC phase shiſt oscillator” category, and uses a feedback loop consisting of RC circuits creating a phase shiſt to generate alternating output. Tere are over 23 other types and categories of oscillators. Due to their
widespread use, it is important to explore their performance against the behaviour of a battery power supply, especially if this supply drops below a nominal voltage. Figure 1 shows a typical oscillator
circuit, which we will use in our experiment. It’s based on the 555 timer IC, with a 4.5V power supply (Figure 2). Its output frequency is about 2.4kHz.
Methodology To assess this oscillator’s behaviour, it was connected to a variable power supply, with output varying from 1-6Vdc. At each step, its peak-to-peak amplitude and output frequency were logged; see Figure 3, which shows that the amplitude relates proportionally to the power supply voltage, changing at a rate of 0.59V peak- to-peak with each 1Vdc change in supply voltage.
Another finding is that these
changes occur only within the 2.5- 5.9Vdc window, outside of which the signal is drastically attenuated. Electronic system designers need to consider these findings when developing their circuits for an application. In our experiment, the output
frequency readings were plotted against the changing power supply voltages; see Figure 4, which shows that the oscillator’s output frequency drops about 300Hz for every 1Vdc drop in supply voltage. Similarly, the output jumps in frequency when the supply voltage drops below 2.5Vdc; it caps at 12.93kHz. The findings lead to the conclusion that the oscillator output’s peak-to-peak amplitude and frequency are very vulnerable to power supply changes.
Figure 1: A popular oscillator circuit using the 555 timer IC 12 May 2022
www.electronicsworld.co.uk
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