Project Files of TIP122 Darlington Library for Proteus: TIP122 and TIP127 in TO-220

TIP122 DARLINGTON LIBRARY FOR PROTEUS - V1.0 (TIP122 and TIP127 Darlingtons in TO-220 with a heatsink and a pop-up)
Designed by The Engineering Projects
www.TheEngineeringProjects.com

IMPORTANT LINKS
Article (read it first - pictures, step by step, every feature explained):
  https://www.theengineeringprojects.com/2026/11/tip122-darlington-library-for-proteus.html
Report a bug or suggest a feature (our forum):
  https://www.theengineeringprojects.com/forum/category/tip122-darlington-proteus-library
The demo runs on our Arduino UNO V4.0 (included) - working LEDs, RESET and a
built-in serial monitor, no Virtual Terminal to wire - its own article:
  https://www.theengineeringprojects.com/2026/10/arduino-uno-library-for-proteus-v40.html
The demo's loads are our own power resistors (included):
  https://www.theengineeringprojects.com/2026/11/power-resistor-library-for-proteus.html
its level shifter is our own BC547B (included):
  https://www.theengineeringprojects.com/2026/11/small-transistors-library-for-proteus.html
Support us (the libraries are free):
  https://www.theengineeringprojects.com/donate

FILE STRUCTURE
TIP122-Darlington-TEP-v1.0/
|-- Proteus Library Files/
|   |-- ArduinoV4TEP.LIB                              201.9 KB   TEP Arduino boards V4.0 (UNO) -> LIBRARY
|   |-- TEPBJT.LIB                                     18.6 KB   a part the demo uses -> LIBRARY folder
|   |-- TEPPOWERRES.LIB                               157.2 KB   a part the demo uses -> LIBRARY folder
|   |-- TEPRESISTOR.LIB                               306.9 KB   a part the demo uses -> LIBRARY folder
|   |-- TEPTIP.LIB                                     15.2 KB   the library -> LIBRARY folder
|-- Proteus Model Files/
|   |-- TEPARDUINO.DLL                                883.5 KB   the Arduino board model -> MODELS folder
|   |-- TEPBJT.DLL                                    292.0 KB   its model -> MODELS folder
|   |-- TEPPOWERRES.DLL                               304.5 KB   its model -> MODELS folder
|   |-- TEPRESISTOR.DLL                               311.0 KB   its model -> MODELS folder
|   |-- TEPTIP.DLL                                    294.5 KB   the model -> MODELS folder
|-- Proteus Simulation/
|   |-- Darlington_Demo.hex                             9.6 KB   the demo firmware
|   |-- TEPARDUINO.DLL                                883.5 KB   copy of the board model
|   |-- TEPBJT.DLL                                    292.0 KB   copy of its model
|   |-- TEPPOWERRES.DLL                               304.5 KB   copy of its model
|   |-- TEPRESISTOR.DLL                               311.0 KB   copy of its model
|   |-- TEPTIP.DLL                                    294.5 KB   copy of the model
|   |-- TIP122-TIP127-Darlington-ArduinoUnoV4.pdsprj   25.6 KB   the demo project
|-- Arduino Code/
|   |-- Darlington_Demo/Darlington_Demo.ino             1.6 KB   the demo sketch (source of the .hex)
|-- README.txt                                        ~13.4 KB   this file
Total: 4.81 MB (unzipped). The C++ source code of the models is not included.

WHAT IS IT?
Two TO-220 Darlington transistors, drawn at true scale: the black body 10 x 9 mm under the metal tab
with its 3.6 mm hole, legs B C E (the tab is C).
  * TIP122 - NPN Darlington, 100 V, 5 A, 65 W on a heatsink, hFE 1000 or more.
  * TIP127 - its PNP complement.
  * Inside, as on the real die: Q1 drives Q2's base, R1 (8k) across Q1's base-emitter, R2 (120 ohm)
    across Q2's, and a diode from the emitter to the
    collector. Each transistor is the Gummel-Poon-style law of our Small Transistors library; the
    node between them is solved inside, so the part
    stays a three-pin model and converges like a SPICE transistor.
  * The junction temperature follows the power through the heatsink (HEATSINK = NONE 62.5 C/W, SMALL
    15 C/W, LARGE 5 C/W); past 150 C it warns,
    past 175 C it fails short C to E, until New part.
  * Click one at Run for the pop-up: the region, the parts inside lit as they conduct, the output
    curves with the working point, the temperature,
    graphs, an event log and a check page.
The body is drawn as on the real part and to true scale against our Arduino.
The TEP signature and the pop-up are TEP additions.

TWO DEVICES (search "TIP122" or "TIP127" in Pick Devices):
  TIP122TEP   "TIP122 NPN Darlington V1.0" in TEPTIP.LIB (Transistors > Darlington), prefix Q, model
  TEPTIP.DLL. Pins 1 B, 2 C, 3 E.
  TIP127TEP   "TIP127 PNP Darlington V1.0" in TEPTIP.LIB (Transistors > Darlington), prefix Q, model
  TEPTIP.DLL. Pins 1 B, 2 C, 3 E.

THE POP-UP
Click the part at Run. Tabs:
    Transistor the region and its junction temperature, the TO-220 drawn with what is conducting
    inside it, the output curves (Ic against Vce at four
               base currents) with the working point, and eight live values. The toolbar: New part,
               the pinout and the heatsink.
    Graphs     the live values over the last 2, 6 or 15 s. Live / Freeze.
    Event log  every change and warning; filters All / Changes / Warnings, Pause, Clear
    Check      what the part is doing and what to look at, each with a verdict (green = fine, amber
    = check, red = wrong)
    Settings   theme, text size, open at Run, window size
    Help       report a bug, suggest a feature, article, updates, donate, forum; Copy diagnostics
    for a bug report

TEST STATUS
V1.0: verified in Proteus 8.5 on 31 Oct 2026 (the demo project as shipped: an A4 sheet, an Arduino UNO V4.0).
What the runs showed (the model's own numbers and the sketch's monitor):
  * The project loads and starts cleanly; the +12V labels join the +12V power terminal. (Before the
    runs, the Darlington law was checked against a
    separate Newton solution of both demo circuits: 0.514 A and 0.515 A, as the run then showed.)
  * Step 1, TIP122 on: 3.62 mA into its base through 1k, 514 mA through the 22 ohm load, Vce 0.68 V,
    Vbe 1.31 V (0.67 V + 0.64 V, the two transistors
    inside), forced gain 142 - saturated; 356 mW, its junction settling at 47 C with no heatsink.
  * Step 2, the TIP122 at 50 % PWM (half the power on average) and the TIP127 on: the BC547B pulled
    4.85 mA through 2k2 and saturated it - 515 mA
    into its load, Vce -0.68 V, 355 mW, the junction settling at 31 C on its SMALL heatsink. The
    load itself: 5.83 W of its 10 W.
  * Step 3, TIP122 off: cut off, 12.0 V across it. The monitor printed every step.
  * The pop-up: Transistor, Graphs, Event log, Check - all four pages followed the run, for both
    Darlingtons.

INSTALLATION (about 2 minutes)
1. Close Proteus. Extract the WHOLE ZIP to a normal folder (e.g. Desktop).
2. Copy everything in "Proteus Library Files" (TEPTIP.LIB, TEPRESISTOR.LIB, TEPPOWERRES.LIB,
TEPBJT.LIB and our Arduino library V4.0, ArduinoV4TEP.LIB, with the ARDUINO UNO V4.0 used by the
demo) to the LIBRARY folder of Proteus, for example:
     C:\Program Files (x86)\Labcenter Electronics\Proteus 8 Professional\LIBRARY
   (use the folder that already holds Proteus's own .LIB files).
3. Copy TEPTIP.DLL, TEPRESISTOR.DLL, TEPPOWERRES.DLL, TEPBJT.DLL and TEPARDUINO.DLL from "Proteus
Model Files" to the MODELS folder (...\Proteus 8 Professional\MODELS).
4. Delete TEPTIP.IDX from the LIBRARY folder if it is there (Proteus makes a new index).
5. Start Proteus. In Pick Devices (P) search "TIP122 or TIP127".

RUN THE DEMO
"Proteus Simulation\TIP122-TIP127-Darlington-ArduinoUnoV4.pdsprj" (an A4 sheet) - keep the .hex file
and the DLLs beside the project.
  ARD1:   Arduino UNO V4.0 running Darlington_Demo.hex, its serial monitor built in (window "TEP
  Arduino UNO - ARD1").
  Q1 TIP122 (low side): D9 - R1 1k - base; +12V - R2 (our 10 W power resistor, 22 ohm) - collector;
  emitter to GND.
  Q2 TIP127 (high side, HEATSINK SMALL): emitter +12V; collector - R3 (22 ohm, 10 W) - GND; base -
  R4 10k - +12V, base - R5 2k2 - Q3's collector.
  Q3 BC547B (our Small Transistors): base - R6 10k - D8; emitter to GND - it shifts the 5 V pin to
  the 12 V PNP.
  1. Press Run. Every 2.5 s the next step: TIP122 on / TIP122 at 50 % PWM with TIP127 on / TIP127
  alone / both off.
  2. Open the pop-ups: the region, the temperature, what conducts inside.
Closed the monitor? Click the UNO's USB port.

WIRING (the same in Proteus and on a real board)
  NPN low side:  +V - load - C;  E to GND;  pin - 1k - B   (a Darlington needs about 1.3 V on its
  base and very little current)
  PNP high side: E to +V; C - load - GND; B pulled up to +V (10k) and pulled down through 2k2 by an
  NPN on the pin (a level shifter)
REAL HARDWARE:
 * Its saturation voltage is 0.7 V or more (more at amps): at 3 A that is 2 W or more - use a
   heatsink.
 * The diode inside runs from E to C: it is not a flyback diode for a motor or a relay - put one
   across the load.
 * The tab is the collector: insulate it from a grounded heatsink with a pad and a washer.
 * A PNP high-side switch on a higher rail than the pin needs a level shifter - never tie a 5 V pin
   to a 12 V PNP's base.

THE DEMO SKETCH ON THE SERIAL MONITOR (Darlington_Demo V1.0, 9600 baud)
There are no commands. The sketch steps every 2.5 s and prints each step.
EXPECTED MONITOR OUTPUT
  Darlingtons - The Engineering Projects
  Step 1: TIP122 on (100 %), TIP127 off
  Step 2: TIP122 at 50 % PWM, TIP127 on

PROPERTIES (double-click the part > Edit Properties)
  Part (VALUE)                     TIP122 or TIP127
  Heatsink                         NONE (62.5 C/W, 2.0 W safe), SMALL (15 + 1.92 C/W, 7.4 W), LARGE
  (5 + 1.92 C/W, 18 W)
Every run starts again from the properties.

LINKS.INI (OPTIONAL)
The Help page cards of the pop-up open web pages. To point them somewhere else without a new DLL,
put a text file named links.ini next to TEPTIP.DLL with lines KEY=URL, for example:
  ARTICLE=https://www.theengineeringprojects.com/...
Keys: WEBSITE, FORUM, BUG_REPORT, FEATURE_REQUEST, ARTICLE, USER_GUIDE,
UPDATE_CHECK, DONATE. Only http:// and https:// links are used; lines starting
with # are comments.

TROUBLESHOOTING
* It stays ACTIVE with several volts across it: not enough base current - a smaller base resistor.
* TOO HOT: the junction passed 150 C - a bigger heatsink, or switch it hard so Vce stays low.
* The TIP127 never turns off: its base must go all the way up to its emitter's rail - check the
  pull-up.
* DIODE ON: current runs from E to C through the built-in diode - a coil's kick or a reversed
  supply.
* The part is not simulated: TEPTIP.DLL is missing from MODELS and from the project folder. No UNO /
  no monitor window: TEPARDUINO.DLL is missing, or click the UNO's USB port.

BUG REPORTS AND FEATURE REQUESTS
Please post them in our forum with a screenshot, the Serial Monitor text, the
simulation log and the pop-up's Copy diagnostics text:
  https://www.theengineeringprojects.com/forum/category/tip122-darlington-proteus-library

SUPPORT US
This library is free. If it saves you time, please support our work:
  https://www.theengineeringprojects.com/donate

WEBSITE
  https://www.theengineeringprojects.com/

LICENCES AND THIRD-PARTY NOTES
* The model (TEPTIP.DLL), the symbols and artwork, the other parts of ours in the demo and the
  Arduino Library V4.0 (ArduinoV4TEP.LIB / TEPARDUINO.DLL, with its built-in TEP Serial Monitor
  Advance) are made by The Engineering Projects. The models use only standard Windows libraries; no
  Visual C++ redistributable is needed.
  The C++ source code is not included.
* Arduino UNO V4.0 (ArduinoV4TEP.LIB / TEPARDUINO.DLL, our Arduino Library V4.0 - its
  microcontroller is Proteus's own AVR model): The Engineering Projects,
  https://www.theengineeringprojects.com/2026/10/arduino-uno-library-for-proteus-v40.html
* The .hex file is built from the demo sketch and the Arduino AVR core 1.8.6, which includes
  LGPL-licensed code; its source code is available at
  https://github.com/arduino/ArduinoCore-avr/tree/1.8.6
* Proteus is a product of Labcenter Electronics and is not included. Arduino is a trademark of Arduino SA.
  This library is not made or endorsed by Arduino or Labcenter.

REBUILDING THE FIRMWARE (OPTIONAL)
The HEX file is supplied; Arduino IDE is not needed to run the demo. To edit the sketch, open
Arduino Code\Darlington_Demo\Darlington_Demo.ino, select Arduino Uno and use Sketch > Export
Compiled Binary. Replace the simulation's .hex with the exported HEX. The sketch needs 3,498 bytes
of flash and 307 bytes of RAM.

MODEL SCOPE AND LIMITS
Modelled: both transistors inside, the two resistors and the diode, the Early effect and high
injection, the regions, the power, the junction
temperature through the heatsink, and the short-circuit failure.
Not modelled: the switching times, the second breakdown, the case-to-sink pad.

VERSION
TEP TIP122 Darlington library V1.0 (Nov 2026). Devices TIP122TEP and TIP127TEP (TEPTIP.LIB /
TEPTIP.DLL). Demo sketch Darlington_Demo V1.0. Demo board: ARDUINO UNO V4.0 (TEP Arduino Library
V4.0) with its built-in serial monitor.