HelloTIP122

Created by Pavly G.

A showcase for the use of TIP122 with the avr GPIO.

Topics Covered:

1) TIP122 Electrical Characteristics.

2) TIP122~AtMega32A Connection.

3) Calculating the circuit characteristics.

1) TIP122 Electrical Charachteristics:

Absolute Maximum Ratings	Electrical charachteristics Test

2) TIP122~AtMega32A Connection:

This image illustrates the connection between atmega32A GPIO PB2 and TIP122 Base terminal:

3) Calculating the circuit characteristics:

1-Calculating the suitable resistor for the 1v7 RED LED:

Using KVL (Kirchhoff's Voltage Law): 
Vcc = V1 + V2 + ....
Vcc = V(LED) + V(RL) + V(CE)
9v = 1v7 + I(c) . R(L)
; Let, I(c) = I(LED-max) = 20mAmps = 20/1000 = 0.02 amps.

Then, 
R(L) = (9v - 1v7) / 0.02amps = 365 OHMS.

2-Calculating the total I(c) Current draw when connecting the circuit at the CE terminal:

From these findings:

Voltage Drop across the load resistor "RL"	Amperage Reading across the CE terminal using the above circuit (I(C))

Using Ohm's Law (I = V/R), find the battery current draw (not the same as I(c)) at the CE circuit: 
I(draw) = V(RL) / R(L) 
     = 4v25 / (330 OHMS) = 0.01288 amps.

Finding the BETA (Current Gain) value constructed by this circuit: 
- Remove the LED and the Load Resistance as they limit the current draw affecting the I(C) and the recording.
- Calculate I(B) and I(C) and plug them into this equation:
> B = I(C) / I(B) = 0.1amps / 0.8mAmps = 0.1 / (0.8 / 1000) = 125.

The TIP122 Darlington can provide over 1000 hFE as a current gain using the proper current at both the CE circuit and the BE circuit.