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The 2SC appears ln566 be an older component and may be hard to come by sim and layoutbut there are several medium power transistor replacements that might work and there are several available in the Multisim database.

Message 3 of 7. It isn’t designed for audio use, and has higher distortion than most other opamps. Figure 4 – Diode Sinewave Shaper.

A few years ago, you’d simply get an IC that did almost everything for you – the NE was a good example, and needed few external parts to make a simple, high performance VCO. It’s been assumed that you need a VCO with a triangle wave output that can be converted to a sinewave, and a squarewave with equal mark-space ratio.

Because most are unable to pull the output voltage down to the negative supply, we need to add an extra resistor R9, Figure 3 to ensure that the transistor Q1 will turn on and off properly. A positive modulation voltage causes the frequency to increase, and vice versa.


Voltage Controlled Oscillator-VCO theory and working|LM IC

Using a ground reference for the input stage of a dual supply version also means that the modulating voltage AC, DC or a combination of the two must always be positive.

The circuit relies on feedback, and even a seemingly trivial error will stop it from working. Few provide a triangle wave output though, and with many the output is a pulse waveform, rather than a squarewave equal on and off times. If you want to build any of the circuits shown, you’ll need to use Veroboard or similar. The voltage will be around Ok sorry about that, I must have used “LM5” in the Multisim quick search which brought up the timers and I didn’t see the discrepency.


The IC has a very linear modulation characteristic and has excellent thermal stability. The output frequency of the VCO can be obtained using the following equation: Note that if any opamp is used that cannot swing its output voltage to the negative rail, an extra resistor must be added between the base and emitter of Q1, or it will be unable to turn off.

The datasheet shows a formula for frequency, and with the values given in Figure 1 it works out to be 1kHz if the ‘Set Base Frequency’ pot is set for 6V.

LM Frequency deviation problem Ask Question. For this, waveform purity isn’t a major concern, but you do need a constant amplitude regardless of frequency.

(PDF) LM566 Datasheet download

The circuit as shown expects an input voltage of around 8V peak-peak, as will be obtained from the circuit shown in Figure 3. This depends on what level of accuracy you need.

What happens if you connect C7 to ground instead of RV11? It does allow the modulating signal to be direct coupled, but that doesn’t necessarily provide any advantages. Linear voltage controlled oscillators are generally used to produce a sine wave. VCOs are used for tone generators, frequency modulators, clock generators, function generators, music synthesisers and frequency shift keying FSK, a radio transmission system where digital information is transmitted via discrete frequency changes of a carrier wave.

Dahasheet be afraid to use enough words to explain your problem unambiguously. The datasheet shows a pair of fixed resistors, but I’ve shown a pot that lets dagasheet set the dxtasheet frequency. Does this affect the frequency change you observe in any way? The input can be driven to greater than 12V, but with somewhat reduced linearity.


I’ve included it here purely for the sake of completeness and to show how easy it was to make a VCO a few years ago. The control voltage input needs to be biased to some voltage that gives you the base frequency you need. Despite appearances, the input will not be at zero volts when the pot is centred.

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This is best classed as a ‘general purpose’ oscillator that lends itself well to non-critical applications. An opamp VCO circuit is shown in the LM opamp datasheet, and that’s the basis for the design shown here. The VCO can be operated from a dual dataxheet, and that only entails a few minor changes.

While the LM is quite ok for a fairly basic VCO, it doesn’t scale well to higher frequencies above 5kHz or so because it’s a low power opamp with very basic specifications. The LM circuit is shown above. Sign up using Facebook. The reason for using a circuit like those shown below is – first and foremost – to be able to get a passable sinewave output.

If your version only has the timer you can use 2 for simulation purposes or create one for PCB layout. As shown, four diodes are used to clip the triangle wave in such a way as to get minimum distortion.