Low Power Oscilator

[iv_eleven]

Hello,

I need to design a low power oscilator for a project using an CD40106BC Hex Schmitt Trigger ( https://www.floka.com/cmos/pdf/40106.pdf#search=%22CD40106BC%22)
You can find the curcuit in the datasheet document. The input voltage is 4,8 V and i must get an frequency of 4 khz. The problem is that i don't know R and C. Can someone please help!!

P.S. Sorry, but my english isn't great.

 

[stevez]

Do you need a sine or square wave that rises above and below zero volts - or a square form that goes from nearly zero to about 5 volts (or whatever)? If you can find a 555 that works at the voltage you have you might try that. See the datasheet for LM555 as a start. It shows how to determine the R and C values.

 

[iv_eleven]

I need a square orm that goes from nearly zero to about 5 volts, and i need to use exactly the low power oscilator circuit described in the CD40106BC' s datasheet

 

[JimB]

If you look at the datasheet, to the right of the circuit diagram are some formulae.

One of them gives the frequency. The frequency is only approximate and the formula is a bit involved. But it can be resolved to:

F = 1/(2RC) (for a 5volt supply at 25degC)

If you want 4khz, make C = 0.1uF and R = 1250 Ohm.
Be prepared to change the value of the resistor if you want an accurate 4kHz.

JimB

 

[iv_eleven]

The problem is that i need to determine the parts. I need to know what value do Vt- and Vt+ have, to determine the parts. For example, what are thos values for C = 0.1 uF.

 

[Roff]

The formula for frequency (f) can easily be solved for RC. Once you have done that, simply plug in the values of f, VT-, VT+, and VDD.
You can get VT- and VT+ from the specs in the datasheet. Unfortunately, they are not tightly controlled, so your frequency will not be very predictable.

 

[audioguru]

An ordinary Cmos inverter can provide only a small output current, which is even less at the low supply voltage of 4.8V. So I think the resistor value in the oscillator should not be less than 10k ohms. Therefore the capacitor value will be about 0.01uF. The resistor could be a 25k pot in series with a 4.7k resistor to allow you to set the frequency.