Ron H said:Well, you can't saturate a transistor that has no current limiting resistors in the collector-emitter circuit, but you can draw a lot of current! With a 4.7k base resistor, a 3 volt supply, and a beta of 100, collector current will be about 50 ma. This is the absolute maximum collector current for this part.
Also, Ft is spec'ed at Vce=10V and Ic=8ma, Which is probably the optimum point. It will probably be less than that for any other combination of voltage and current.
mstechca said:I guess that means my long-range circuit (in the middle) is almost always under saturation. The audio is connected to the collector of the NPN.
I can't connect the audio output to the NPN's base because
1) I'm asking for inversion,
2) It will jeopardize the frequency of the transmitter portion set by the 330pF capacitor and the 4.7K resistor, and
3) the gain is lower.
The transistor has too much base current because the value of the base resistor is too low, therefore the transistor doesn't work properly.mstechca said:I'm ok with heavy saturation, because I want the signal to get through.
A 555 oscillator oscillates when its reset pin is at +ve. It is reset and won't oscillate when its reset pin is at ground.As I said, it works great when the reset pin is connected to +ve. When the reset pin is connected to -ve, it doesn't work. Sometimes, the wrong audio tone is emitted!
A 47uF electrolytic capacitor is an inductor at radio frequencies. It is fine for audio but a 330pF to 2000pF ceramic disc cap is an RF supply bypass.I am using 47uF battery coupling capacitors, and it even does not make a difference.
If I use inversion, doesn't that mean I need to remove the coupling capacitor between the audio stage (the 555 circuit), and the transmitter stage (the circuit in yellow)?What difference does that make?.
I have tried 9.1K but the range is much lower, and the circuit just about doesn't work when the battery drains to about 1.5V from 3V.Haven't you tried increasing the value of the resistor?
maybe that is my problem.A 47uF electrolytic capacitor is an inductor at radio frequencies. It is fine for audio but a 330pF to 2000pF ceramic disc cap is an RF supply bypass.
Someone (I think Audioguru) mentioned that such a configuration creates a low-pass filter. I'll take your word. I suppose I should calculate Xc of the capacitor and make the answer as close to 0 as possible with my frequency.Neither of those components set the frequency - you still appear to have no clue how it works?. I'm sure we've told you before?, but the 4.7K is the base bias resistor (and too low), and the 330pF grounds the base at high frequencies to allow the transistor to operate in common-base.
I don't understand how you got about 50ma. According to my calculator,With a 4.7k base resistor, a 3 volt supply, and a beta of 100, collector current will be about 50 ma. This is the absolute maximum collector current for this part.
My emitter is connected to a tuned circuit. I use "gang-tuning".(not helped by replacing the emitter resistor by an inductor - for some bizarre reason?).
For now, I'm just gonna address the BJT current issue. The little schematic below should explain it. This is not a simulation. If the beta is not 100, the collector current will be different, as shown by the equation.I don't understand how you got about 50ma. According to my calculator,
3V / 4700 ohms = 0.000638298 amps
which is 638uA, going from +ve to NPN's base.
It is the NPN's base which turns on the transistor.
Between yesterday, and today, I kind of figured it out. Thanks for clarifying it.The little schematic below should explain it. This is not a simulation. If the beta is not 100, the collector current will be different, as shown by the equation.
I upped my resistor to 6.2K which makes the collector current a few mA short of the maximum limit. The PN3563 accepts a 50mA maximum safely.Ron H said:It's just drawing too much current
...and you have no feedback to control the bias point.
Since it obviously can't boost signal current, it only seems reasonable to expect it to boost signal voltage.
My inductor in DC mode is a very low-value resistor, and in AC mode at VHF, it probably is a bit higher. A resistor, if high enough can make performance suffer.A resistor between emitter and ground will provide negative feedback.
I have a question. Why a resistor instead? They limit more current.If you insist on having an inductor in the emitter circuit, you still can - in series with a resistor.
The resistor advice has. I want to avoid current limiting, unless I have to. and in the case of the collector to base resistor, I have no choice, or my transistor will be flying so high, it might hit Audioguru's window :shock: :lol: j/k.I'm not going to offer any RF advice, because previous attempts have proven futile. :roll:
I don't feel any heat. I can agree that a lot of current is used, and it is intentional, because that can make the transmitter operate better, but of course, too much current is bad.audioguru said:High current in a transistor that is caused by having the base-bias resistor's value way too low, and without having an emitter resistor to "regulate" the current causes heat, not output power. It also wastes a lot of battery current.
That is still true even if I have capacitor coupling? (capacitor between 7555's pin 3, and emitter)The 555 has a high output current when it feeds a low resistance load. Your circuit has the 555 driving the dead shorts of high frequency inductors, except when it drives the base.
The output voltage of the 555 is way too high for your circuit and the very low output impedance of the 555's output loads-down your circuit so much that it can't function.
50mA times 3V is 150mW. The battery also warms a little. The 555 that is driving a short warms a little. A huge waste of battery power.mstechca said:don't feel any heat. I can agree that a lot of current is used
No. A transistor is linear. An increase of base current results in an increase of emitter-collector current. Your base resistor's value is too low resulting in too much base current and too much emitter-collector current.Doesn't the resistor connected to the base help limit the current from emitter to collector, or does a transistor function as a latch so that when so much current or voltage is received at the base, the latch is enabled and maximum current flows from emitter to collector?
It does. If its value is higher then the current is lower.I always thought the resistor connected to base has an effect on the entire current consumption.
Calculate the very low reactance of the capacitor at the 555's frequency.That is still true even if I have capacitor coupling? (capacitor between 7555's pin 3, and emitter)
You calculate the effect of the modulating voltage on the current of the oscillator. When the modulating voltage and current are too high then the oscillator is cutoff during parts of the modulation and has its average frequency changed.How do I calculate the optimal voltage?
I think the RF frequency is changed because the modulation is much too strong.I wonder if that is why I hear a random noise instead of dead air when RESET pin is low.
The transistor needs to be biased to a proper amount of current so that it can have a high output voltage swing. It can't if it is conducting too much.I learned that current flows from emitter to collector in a common-base amplifier. If I replaced the inductor with a resistor, I will reduce current consumption, and therefore range will be reduced.
and since negative feedback is degeneration, and since it can reduce gain, I think it is best to avoid it as much as possible. If a resistor is 100% necessary, then maybe an ohm or two is about it.A resistor is connected from the transistor's emitter to ground as negative feedback.
Doesn't the base resistor and/or the inductor connected to the collector limit the voltage to an extent?If the transistor's gain is low, then less voltage is developed across the emitter resistor so its base and emitter-collector currents are increased. If the transistor's gain is high then more voltage is developed across the emitter resistor so its base and emitter-collector currents are decreased.
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