Wednesday, September 8, 2010

Analog Electronics Ready-Reckoner 1

1. Forbidden energy gap for insulator diamond is 6 eV.

2. Drift velocity is in the direction opposite to that of the electric field and magnitude is proportional to electric field.

3. Semiconductor has forbidden energy gap of about 1 eV.

4. Silicon is largely preferred to germanium because of its large gap energy, which provide improved device properties at high temperatures.

5. In a capacitor, the dielectric strength is the ability of a dielectric to withstand a potential difference without breakdown. Air/vacuum has dielectric constant 1.

6. Only electrolytic capacitors have polarity. High value capacitors are electrolytic.  Electrolytic capacitors need to be connected with the correct polarity.  If not, they can explode. 

7. The voltage of a capacitor falls by an equal fraction in equal time. V = V0 e-t/RC
The physics codes are as follows:
  • V - voltage at any time;
  • V0 - the voltage at the start;
  • t - the time (s);
  • - the resistance of the resistor through which the capacitor discharges (W);
  • C - the capacitance of the capacitance (F);
  • e - the exponential number, 2.718...
The charge follows the same pattern:

Q = Q0 e-t/RC

The current follows the same pattern:

I = I0 e-t/RC

The product between resistance and capacitance (RC) that appears in the formula is called the time constant and is measured in seconds.  It may seem strange that ohms × farads = seconds, but it's true.  If we multiply the base units of ohms and farads, we end up with seconds.

8.  Inductors store energy in the form of magnetic field and delivers it as and when required.

9. A missing electron in the valence band leaves a vacant space there, which is known as the hole.

10.  Under thermal equilibrium for any semiconductor, the product of the number of holes  and the number of electrons  is constant and is independent of the amount of donor and acceptor impurity doping. This relation is known as mass-action law, given by:

n * p = ni

n = number of free electrons per unit volume
p = number of holes per unit volume

ni = intrinsic concentration

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