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ELM440SM Datasheet(PDF) 4 Page - ELM Electronics |
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ELM440SM Datasheet(HTML) 4 Page - ELM Electronics |
4 / 4 page Example Application 4 of 4 The ELM440 can be easily configured to provide a 60Hz output as shown in Figure 1 below. A 3.579545MHz crystal is connected to the integrated circuit, along with suitable loading capacitors, and the 60Hz output is then taken from pin 7. Pin 5 is grounded, as no reference signal is supplied. As usual, it is also good practise to place a bypass capacitor across the power supply as well. Figure 2 shows how easily this circuit can be modified to operate in synchronism with the AC power line. A reference signal is taken from one half of a 16Vrms CT transformer winding through a 47K Ω resistor. Both circuits share a common VSS. The resistor was chosen to limit peak currents in this circuit to about 0.24 mA, which is well within the IC’s capabilities. The ELM440 will continue to use this signal as it’s reference, as long as it is available. Upon loss of the AC, the circuit will automatically switch over to using the crystal as a reference. Using a rectifier circuit for the reference signal can pose some problems if one is not careful. Full- wave circuits can be particularly troublesome as all of the diodes may cease to conduct after the peak of the waveform, and the input voltage level is then essentially floating. In this case, at minimum, a large value (470K Ω) resistor should also be connected between the sync input and VSS, to provide a ground reference during these times. Both circuits shown are simple, leaving little room for change. One modification that might be considered for either is to replace one of the fixed value capacitors with a variable one, in order to be able to trim the oscillator frequency for greater accuracy. ELM440 ELM440DSB Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > 60Hz Out 0.1µF +5V 1 2 3 4 8 7 6 5 27pF 3.58MHz 27pF Figure 1. Typical Connections Figure 2. Using the Sync Input 0.1µF +5V 1 2 3 4 8 7 6 5 60Hz Out 27pF 3.58MHz 27pF 47K Ω 8V 8V + |
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