Column: Circuit drill
TTL circuit is typically very low – in the microampere range.
Experiment setup and results Questions relating to this circuit and its performance include: • What happens if the power supply voltage (5Vdc) drops or rises?
• What will the standby current be? • Will the circuit still be stable? Since this circuit is commonly
found in many applications, it is very important to determine the answers to these questions, so we set up the following experiment. We check the circuit’s performance
for several power supply voltages – 3Vdc, 4Vdc, 5Vdc, 6Vdc and 7Vdc. For each one we plot the magnitude of the current passing through the speaker, and also the standby current (with the input voltage above 5Vdc) vs. the power supply voltage (4-7Vdc). We used a 5Vdc Zener diode;
different Zeners can be used for threshold voltages other than 5Vdc. We also assumed the following:
• All component values were kept unchanged.
• Te ambient temperature was kept at 25o
C. Te resulting plots from the
experiment are shown in Figures 2-4. Tese results show that our circuit in Figure 1 draws very low current when in standby mode, or 5Vdc power supply voltage; i.e., in this mode it draws only 144µA. However, the experiment also shows that the circuit draws very high current (in standby mode) when the power supply voltage deviates from the nominal 5Vdc; see Figure 3.
Tis finding is very important for
circuit designers to consider, since they must be aware of this circuit’s limitations. A circuit designer will then either use a stable or regulated power supply to support this circuit, or consider using a different design if low power consumption is crucial for the application.
Figure 2: Output signal amplitude vs. input signal frequency Figure 2: Output signal amplitude vs. input signal frequency
Figure 2: Output signal amplitude vs. input signal frequency
www.electronicsworld.co.uk November 2023 09
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54
