Notes from a class for Analog Electronics

Raymond E. Frey

Physics Office

University of Oregon

Eugene, OR 97403, USA

[email protected] uoregon. edu

December, 99

Class Notes 1

1

Basic Principles

In electromagnetism, voltage is a device of both electrical potential or EMF. In consumer electronics, including the textual content, the term " voltage” refers to the physical quantity of possibly potential or perhaps EMF. Remember that we will use SI devices, as does the text.

As usual, the sign convention for current I sama dengan dq/dt is the fact I can be positive in the direction which usually positive power charge goes.

We will begin by simply considering POWER (i. elizabeth. constant in time) voltages and power to expose Ohm's Regulation and Kirchoﬀ's Laws. We will soon observe, however , why these generalize to AC.

1 ) 1

Ohm's Law

For the resistor Ur, as in the Fig. 1 below, the voltage drop from level a to b, Versus = Vab = Virtual assistant − Vb is given by V sama dengan IR.

I actually

a

n

R

Figure 1: Volt quality drop across a resistor.

A device (e. g. a resistor) which in turn obeys Ohm's Law has to be ohmic. The strength dissipated by resistor can be P = V I = We 2 L = V 2 /R.

1 . 2

Kirchoﬀ's Laws and regulations

Consider any circuit, that is a closed conductive path (for example a battery connected to a resistor via conductive wire), or possibly a network of interconnected routes. 1 . For any node with the circuit in I = out We. Note that the choice of " in” or " out” for virtually any circuit segment is irrelavent, but it need to remain regular. So to get the example of Fig. 2 we have I1 = I2 + I3.

2 . For virtually any closed routine, the amount of the routine EMFs (e. g. battery packs, generators) is equal to the sum in the circuit volts drops: Electronic = V.

Three simple, but important, applications of these types of " laws” follow.

1

I3

I1

I2

Figure 2: A present node.

1 . 2 . 1

Resistors in series

Two resistors, R1 and R2, connected in series include voltage drop V sama dengan I (R1 + R2 ). That is, they have a merged resistance Rs given by their sum:

Rs = R1 + R2

n

i=1

This generalizes for n series resistors to Rs =

1 ) 2 . a couple of

Ri.

Resistors in seite an seite

Two resistors, R1 and R2, connected in parallel have voltage drop Versus = IRp, where Rp = [(1/R1 ) + (1/R2 )]−1

This generalizes for in parallel resistors to

n

1/Rp sama dengan

1 . installment payments on your 3

i=1

1/Ri

Volts Divider

The circuit of Fig. 3 is called a voltage divider panel. It is probably the most useful and important routine elements we all will come across. The relationship among Vin = Vac and Vout = Vbc has by

R2

Vout sama dengan Vin

R1 + R2

1 . a few

Voltage and Current Resources

A ac electricity source gives a constant ac electricity regardless of the current it generates. It is an idealization. For example a battery could be thought of as a voltage origin in series with a small resistor (the " internal resistance” from the battery). When we indicate a voltage Sixth is v input to a circuit, this really is to be regarded a volt quality source unless otherwise stated. A current supply delivers a consistent current regardless of output volts. Again, this really is an idealization, which can be a good approximation used over a selected range of output current, which can be referred to as the compliance range.

2

R1

Vin

R2

Vout

Number 3: A voltage divider.

1 . four

Thevenin's Theorem

Thevenin's theorem states that any circuit consisting of resistors and EMFs has an equal circuit that includes a single voltage source VTH in series with a solitary resistor RTH. The concept of " load” is useful at this point. Look at a partial routine with two output points held by potential diﬀerence Vout which can be not linked to anything. A resistor RL placed through the output is going to complete the circuit, allowing current to ﬂow through RL. The resistor RL is often said to be the " load” to get the routine. A load coupled to the output of your voltage divider panel circuit is definitely shown in Fig. 5

The pharmaceutical drug for ﬁnding the Thevenin equivalent quantities VTH and RTH is as follows: • For a great " open circuit” (RL → ∞), then VTH = Vout. • For a " short...

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