TDA7000 set frecuency
Hi,
Vco, there is a LC resonant, frequency us set with Cv.
Klaus
Thanks. And Cs an Cp? What they do?
between the 5 and 6 pin there is a LC circuit, that generate the frecuency and it is
?
Hi,
all three capacitors set the range of frequency.
Cv is the one variable capacitor to select the frequency = channel = radio program.
The lower frequency limit is when Cv is maximum... and the upper frequency limit is when Cv is minimum.
For a raw estimation Cp is (most) responsible for the max frequency = when Cv is considered to be about 0pF (wich is not possible)
Your formula seems to be correct on first sight.
Klaus
The TDA7000 has not been manufactured for many years. It had many problems. I was replaced by the TDA7088 that has been discontinued by Philips but cheap Chinese "radios" from The Dollar Store use a Chinese copy and they work very poorly.
Now I'm making the pcb but the 75Ohms resistor ?it's the antenna's impedance? or ?it's another resistor?
Why don't you use the pcb design showed in the old datasheet of the TDA7000 IC? It shows the antenna connected to the 220pF capacitor C13 without a 75 ohm resistor.
The 75 ohms resistor Rs is used when the input is from a signal generator. The schematic of the newer TDA7088 shows a schematic with an antenna but without Rs. Rs is shown when the signal is from a signal generator.
Ah, thank. I'm not sure the output power (the datasheet not say). I going to do a class A amplifier with a simple bc548. What you do think? It's necesary? because I just need to hear the voice
Why it's necesary that 75 Ohms resistor?
The datasheet of the old TDA7000 IC shows that its output level is 75mV into its load resistor RL which is 22k ohms when the power supply is 4.5V. The level is too low and the load resistance is too high to use headphones or a speaker so a power amplifier is needed. Most low voltage low power amplifier ICs are not made anymore but since you found an old TDA7000 IC then maybe you could also find an old TDA7052 low power amplifier IC with old through-holes pins or a new surface mount one. A BC548 transistor is not powerful enough to drive headphones or a speaker.
The 75 ohms resistor replacing the antenna is used only when testing the radio with a signal generator.