# 4046 resistor capacitor frequency ranges?

Discussion in 'General Electronics Chat' started by electronice123, Jun 21, 2009.

1. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
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I have been studying the 4046 datasheet but can't make sense of the diagrams that show the frequency and the resistor capacitor combos.

I need my 4046, which operates on 10V, to produce a frequency in the range of 10kHz-20kHz.

What resistor capacitor combination do I need to do this?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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These graphs won't give an exact solution. You might need to add trimming pots to R1 & R2 if you want exactly 10-20kHz.

From Fig 8 of 4046 data sheet locate fmin = 10kHz line. Typical R2 values are given for 10V operation which intersect the 10kHz line. Suppose you select R2=10k @10V. Drop down to the C1 axis from the intersection of the 10kHz line and the 10V R2=10k line. This gives a C1 of about 13,000 pF or .013uF. You could take a nearby preferred value of 0.012uF.

From Fig 9 for fmax/fmin = 2 you get R2/R1 as approximately 1. So R1 could be set as 10k as well. As I suggested if you want to "exactly" set fmax and fmin put some trimming resistors in series with R1 & R2.

Say make R1=R2=4.7K and use a 10k trimmer in each case. Initially set the total [R1 & R2]values to around 10k in each case and then iteratively trim both with a frequency meter to monitor the changes. You will need to vary the VCO control voltage between max & min at the same time, so it will be a "fiddly" business.