Electronics

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Revision as of 03:56, 14 September 2017 by Leo (talk | contribs) (zener)
This page was last edited on 14 September 2017, at 03:56.

Physics

Some formulas that are fundamental:

  • Ohm's Law: V=IR

From Ohm's law, power generation is P=VI (watts)


Diodes

   Anode (+)         Cathode (-)
   ----------[   |]----------

   Electronic symbol:
             | \  | 
   ----------|   >|---------
             | /  |
  • Forward bias = on, lets current pass through
  • Reverse bias = off, restricts current completely

The I-V curve shows relationship between voltage and current. The ideal diode will allow all current through at any forward voltage and no current at any reverse voltage. A real diode will have some limitations:

  • Forward voltage (Vf) - voltage at which the diode turns on and allows forward current to flow. This is the voltage that is required for the diode to be in forward bias
  • Breakdown voltage (Vbr) - the negative voltage which the diode fails to stop current from flowing backwards. You can expect the diode to withstand this voltage in the reverse bias before reverse current flows freely. A diode in breakdown is not necessarily broken. What breaks it is the amount of current that goes through it in this state because the diode does not limit the current.
  • Forward voltage drop - the voltage that is 'lost' by going across the diode

Diodes will have a maximum forward current with the limitation typically because of heat dissipation. This means there will be two maximums: One that is constant (maximum forward continuous current, IF) and one that is peak.

Determining the forward voltage with a multimeter can be done by using the test option across the diode. Test by connecting the black probe to cathode (the side of the diode with the black stripe) and the red probe to anode.

Example Components:

  • 1N4148 Signal Diode
  • 1N4001 Rectifier Diode (for rectifying power)


Zener Diode

  • Has a specific zener breakdown voltage which allows current to flow in reverse bias
  • Zener breakdown voltage is typically labeled with the device. Eg. 5V1 = 5.1 volts

Can be used to create a constant voltage reference by exploiting the breakdown voltage. Any excess voltage will be 'spilled' over via the zener diode.

The resistor is required in order to limit current that can pass through the diode. Because of this design, attempting to use a zener diode as a voltage regulator for a load is inefficient since a lot of power is wasted with the resistor. For high load or a large voltage difference, the resistor will generate a lot of heat (P=IV).

Transient Voltage Suppression (TVS) Diode

A TVS diode is similar to two zener diodes that are connected together in opposite direction. Connecting this to a circuit will prevent voltage from spiking past a certain voltage. It does not conduct in either direction until the breakdown voltage is reached.