An electronic oscillator - Page 1
Forum section: electronics / beginners

author: Bondguy
author_rank: Contributor
timestamp: December 29, 2017, 07:20:49 pm
content: From a definition that an electronic oscillator converts the direct current signal into an alternating current signal,I understand that I must supply DIRECT current FIRST and then I receive ALTERNATING current signal.But if I measure voltages on that oscillator , why do I measure alternating voltage ONLY?Where is the DIRECT signal that was supplied to the crystal first?

author: Audioguru
author_rank: Super Contributor
timestamp: December 29, 2017, 07:28:54 pm
content: An oscillator circuit is powered by a DC voltage and current. You can measure the DC.Oscillation might begin by the sudden input voltage change when the power supply is turned on or by noise in the circuit.

author: Bondguy
author_rank: Contributor
timestamp: December 29, 2017, 09:36:23 pm
content: Yes, but when the oscillation starts, I can measure the oscillation ONLY( AC voltage). Where is DC voltage - the crystal is still supplied with DC voltage.

author: barry14
author_rank: Regular Contributor
timestamp: December 29, 2017, 10:13:52 pm
content: Where are you making your measurements? The output of most oscillators is an AC signal with no DC by design as that is the most useful signal to apply to other equipment. However, internally, the oscillator is supplied with DC to power the circuits that generate the AC signal. Some function generators do have an offset feature so that a DC level (either positive or negative) can be added to the output signal. Note that the DC power to the oscillator circuits must be continuously applied or the AC signal will disappear.

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2017, 10:44:38 pm
content: Quote from: Bondguy on December 29, 2017, 09:36:23 pmThat's the whole point of an oscillator: DC in, AC out.What you most likely have is both AC and DC on top of one another. Please pose a schematic.

author: danadak
author_rank: Super Contributor
timestamp: December 29, 2017, 11:30:02 pm
content: In general terms an oscillator takes in energy, AC or DC, andproduces an ac signal that has some specific characteristic, notnecessarily related to the energy source used. Typically in ourterms a waveform with a specific frequency(s).In short wavelength work, optical spectrum and above, the oscillatoris pumped by an ac signal and produces, typically, a fixed frequencyof light or wave.Regards, Dana.

author: Bondguy
author_rank: Contributor
timestamp: December 30, 2017, 07:37:14 am
content: My problem is that oscillator has a lower frequency than it should have.I replaced crystal and frequency is still lower. So I expect that DC voltage is lower, so that frequency is also lower. Is it possible? Or what can be a reason for a lower frequency?

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: December 30, 2017, 08:21:24 am
content: More likely there is some other feedback mechanism than the crystal causing a lower frequency oscillation. If the feedback is way too strong, then one of the capacitors in the feedback loop may be acting as the timing component instead of the crystal. A smaller capacitor may solve this.The DC is usually blocked form reaching the output by a capacitor. Though at higher frequencies a transformer may be used.