# The Minimum voltage requirement for an RC Oscillator

• leehyong
In summary, the oscillator will not work unless the voltage is higher than 5v. The minimum voltage requirement for this circuit is 10v.
leehyong
Hi
I am trying to run an RC oscillator using a 2N3904
The circuit looks like the following.

I want to run it at 0-5v but I failed, I assume it is because the voltage is not high enough?

What would you expect the minimum voltage requirement to be for this type of circuit.

Delta2
Did you DESIGN the circuit based on some assumptions/requirements for th DC operational point?
Did you recalculate this operational point? Do you know (from oscillator theory) how much gain is necessary?

leehyong said:
I assume it is because the voltage is not high enough?
Hi leehyong.

Possibly it could be insufficient supply voltage.

Two independent set of conditions must be met. The first involves DC biasing: if you remove all of the capacitors from the circuit then what you are left with must set the transistor's operation comfortably within its active region (linear amplifying).

Are you able to analyse the circuit with all capacitors missing to determine the expected DC voltage at its 3 nodes?

What do you plan to use the oscillator for?

NascentOxygen said:
Possibly it could be insufficient supply voltage.
That`s for sure.
A rough calculation of the base voltage (forgetting the base current) gives only app. VB=5*10/110<0.5 volts.

The 100k : 10k voltage divider sets the transistor base bias voltage.
It will need at least a 5V supply before the transistor begins to turn on.
I would remove the 10k between the base and ground then find a minimum voltage.

With a little tweaking of component values this should easily run on 5 volts.

Averagesupernova said:
With a little tweaking of component values this should easily run on 5 volts.
Yes - of course. Therefore my question in post#2 if the OP has designed the circuit.

There are a number of problems with this circuit, all of which conspire to prevent oscillation. One is the time it takes to start, if it ever does. Spice simulation shows it does not start until the supply voltage reaches about 8V.

Another problem is the gain of the transistor amplifier needed to overcome the losses in the phase shift network at the frequency of operation. The emitter capacitor needs to be increased to raise the gain at lower frequencies. Scaling the frequency down by increasing the capacitors in the feedback circuit necessitates increasing the emitter capacitor to restore that gain. That was not done with the OP circuit.

The emitter resistor needs to be reduced to enable the transistor amplifier to drive greater loads on the output without killing the oscillation.

I am always surprised when - as in the present case - somebody seems to have a problem and is asking for help, but is not willing to give requested additional information. Even worse - sometimes it seems that he is not interested anymore. Really a bad behaviour.

sophiecentaur
Measure the volts across the 390R in the Emitter. It should be more than Zero, which it will be if the transistor does not turn on. (due to wrong base bias volts)
If you disconnect the 10k resistor in the base, the Emitter Volts should go to a non zero value. From the diagram, it looks like a simulation.
Please take note of the above post (from LvW), if you want any more help . . . . . ever.

## What is an RC oscillator?

An RC oscillator is a type of electronic oscillator circuit that uses a combination of a resistor and capacitor (RC) components to generate an oscillating output signal.

## What is the minimum voltage requirement for an RC oscillator?

The minimum voltage requirement for an RC oscillator depends on the specific circuit design and components used. However, in general, most RC oscillators require a minimum voltage of around 3-5 volts to operate.

## What happens if the minimum voltage requirement for an RC oscillator is not met?

If the minimum voltage requirement for an RC oscillator is not met, the circuit may not be able to generate an oscillating output signal. This can result in the oscillator not functioning properly or not functioning at all.

## Can the minimum voltage requirement for an RC oscillator be exceeded?

Yes, the minimum voltage requirement for an RC oscillator can be exceeded. However, exceeding the minimum voltage may cause the oscillator to operate at a higher frequency or produce a distorted output signal.

## How can I determine the minimum voltage requirement for a specific RC oscillator circuit?

The best way to determine the minimum voltage requirement for a specific RC oscillator circuit is to consult the circuit's datasheet or consult with the manufacturer. Alternatively, you can also calculate the minimum voltage requirement based on the circuit's components and design.

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