why is a transistor always grounded via a resistor?

Answer 1

Not true.
Transistors have three terminals and depending on the application, one or two of them may be grounded. A resistor is sometimes, NOT ALWAYS, used to bias one of its terminals to some voltage. A resistor may also be used to protect the transistor.

Answer 2

There are several reasons why a resistor may or may not be required in a transistor circuit.

Transistors used for digital logic (i.e. TTL) circuits act as switches. When bipolar transistors are used, uslually the emitter is grounded directly, and a resistor may be used in series with the base to limit base current. The collector then is usually pulled to the bias voltage (Vbias) by a resistor, and then the collector voltage indictes a 1 (Vbias) or 0 logic level. An exception to this is less common ECL (emitter coupled logic).

In the case of analog amplifier circuits, there are several configurations, the most common being common emitter or common source (in the case of MOSFETs), and sometimes common base in Class C amplifiers. In these analog circuits, resistors are used to control bias for class of operation (how long the transistor conducts current during 360 degrees of phase) and may also limit transistor saturation current, as well as match the impedance of a transmission line. Where the resistors are located depends on how the amplifier is intended to work;

In switching power supply applications, transistors (usually MOSFETs) are intended to run either in saturation or cutoff. Any time spent operating other than those two conditions reduces the efficiency. When the transistor is in saturation, the ideal transistor has zero resistance (a short), and obviously it is an ideal open when in cutoff. These circuits usually don't require any resistor to ground.

Answer 3

Not necessarily. But generally there does need to be at least a resistor in either the collector or emitter lead to limit current through the transistor, as when transistors turn on, the collector is nearly shorted to the emitter. If there were no current-limiting resistor in one of the 2 leads, the transistor will burn itself out.

There is nearly always a resistor in the base lead too, to limit base-emitter current to a safe level.

Transistors are current-controlled devices. Therefore you control the current with resistors, so that it can control the transistor.

Answer 4

When it is grounded through a resistor the current flow through that resistor and the resulting voltage drop through the resistance is what puts a specific voltage onto that terminal. Whether you need that resistor depends on the circuit function the transistor is performing.

Answer 5

It's not always true it depends on the circuit. For example,a transistor in common-emitter is usually grounded via a resistor. Because this resistor acts as a negative feedback. (thermal compensation).If Vbe increases because of increase in thermal, the current will increase, so the voltage on resistor will increase too, and then it decreases Vbe.

Answer 6

because if you take the circuit and the charge on the left alpha of the transistor, it becomes grounded.

Answer 7

Negative feedback