PrescottDan
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Since the NPN transistor has a positive supply and ground then why would the input ever be negative?In the top circuit with the 3 diodes to ground:
1) Are the diodes forward or reverse biased? Depends on the Input polarity?
Yes a forward-biased diode conducts current but no it does not conduct voltage. It has a forward voltage drop.2) Do the diodes conduct current? Yes and conduct voltage
Not much. The typical forward voltage of a conducting 1N4148 silicon diode is about 0.66V at 2mA and is 0.70V at 5mA and is 0.73V at 10mA.3) Roughly how much voltage will be across the 3 diodes? depends on the input voltage
No, when a diode temperature increases then the forward voltage decreases a little exactly the same as the base-emitter diode in a transistor.4) Does the voltage across the diodes increase or decrease when something heats them? Increases , current increases
Yes.5) If the base voltage of the transistor decreases a little does the transistor conduct more or conduct less? conducts less
Yes.6) Does the transistor conduct more current or conduct less current when something increases its temperature? conduct more current
Yes.In the second circuit;
1) If the input is 0V then does the transistor conduct or not? NO, it's off
No. The input diode will never conduct because it is backwards.2) if the input is positive a few volts then does the transistor conduct or not? Conducts
Since the NPN transistor has a positive supply and ground then why would the input ever be negative?
Yes a forward-biased diode conducts current but no it does not conduct voltage. It has a forward voltage drop.
No, when a diode temperature increases then the forward voltage decreases a little exactly the same as the base-emitter diode in a transistor.
With a positive DC offset then the base of the transistor never goes negative. Then the input is positive or 0V.Because the Input signal can be a AC sinewaveform, triangle, or squarewaveform
They use DC offset to raise the DC above the ground so the AC sinewaveform can swing positive and negative without getting clipped off
you don't need a negative power supply, just use DC offset
Of course not. A reverse biased diode conducts no current. A forward biased silicon diode conducts current and has a voltage drop of about 0.7V.So a diode "blocks" voltage and only conducts current? the diode converts a voltage to current?
A rectifier or a rectifier bridge converts AC current into DC current. The rectifier or rectifier bridge passes most of the forward voltage minus the diode voltage drop.Rectified diodes convert an AC voltage into a DC voltage, what you mean a diode doesn't conduct voltage only current?
It does not matter why. Every datasheet shows it.Why does a diode decrease in voltage when the diode or transistor gets hot or increases in temperature?
Absolutely NOT!So when a diode or transistor get hot, the current and voltage is lower that is passing through the diode or transistor and on the transistors output the current is lower?
With a positive DC offset then the base of the transistor never goes negative. Then the input is positive or 0V.
Of course not. A reverse biased diode conducts no current. A forward biased silicon diode conducts current and has a voltage drop of about 0.7V.
Rectified diodes convert an AC voltage into a DC voltage, what you mean a diode doesn't conduct voltage only current?
A rectifier or a rectifier bridge converts AC current into DC current. The rectifier or rectifier bridge passes most of the forward voltage minus the diode voltage drop.
Using a coupling capacitor in input, which will feed the AC into offset present in the base of the transistor.So how do you get a waveform to swing positive and negative on the input to a transistor and output of a transistor when there is only a positive power supply to ground, not negative power supply?
No. Start with a single circuit to get it better. There is a lot to learn with a transistor in a circuit.Then my Oscope would need a current probe to view the waveform
You cant ask and say in that way, Input and output impedance of amplifiers not changing with amplitude of given input signal.When a Transistor is turned OFF or no output on the collector, the collector is High Impedance?
When a transistor is Turned On or has an output on the collector, the collector is Low Impedance?
When a transistor has no input on the base, the base is high impedance?
when a transistor has an input current on the base, the base is low impedance?