Injector_circuit

1. Component list :
Resistor 470Ω X 2
Resistor 820Ω X 2
Transistor BC547 X 2( general purpose switching and amplification)
 - Characteristics 

- Limiting values

Reference by http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf

LED 5mm X 2 (Green)
Circuit board (50mm X 30mm)
Leads X 4

2. Calculations
R14, R15 ?
Supply voltage 12v
LED 1.8V & 20mA The LED consumes 1.8v for its operation and the current of 20mA flows through anode to cathode.
Transistor's voltage drop between collector and emitter 0.2v when the gate is opened.
The voltage drops in resistor R14 and R15 are at 10v. (Vt= Vr + Vl + Vce, Vr=Vt - Vl - Vce)
Vr=12v - 1.8v - 0.2v=10v
The calculations are shown the ohm's law.
V=I X R, R=V/I
R= 10/0.020 =500Ω
Therefore, I chose the resistors value of 500Ω which is near 470Ω for R14 and R15.
R13, R16 ?
PWM0, PWM1  5v (Injector's signals)
Vbe= 0.6v (voltage drop between base and emitter in a transistor BC547)
The voltage drops in resistor R13 and R16 are at 4.4v. (Vt= Vr + Vbe, Vr=Vt - Vbe)
Vr=5v - 0.6v =4.4v
Base to Emitter saturation amps Ib=5mA, Ic=100mA from the BC547 data sheet.
V=I X R, R=V/I
R= 4.4/0.005 =880Ω Therefore, I chose the resistors value of 880Ω which is near 820Ω for R13 and R16.

3. A Technical Explanation

Reference by http://moodle.unitec.ac.nz/file.php/1309/Practical_Worksheets/injector_circuit.docx

This circuit has two individual circuits which is called parallel circuit using 12v supply voltage.
When the PWM0 and PWM1 of input signals at 5v are received in this circuit, the small current flow through base(2) to emitter(3) with operating voltage at around 0.6v. And then, the gate between collector and emitter is opened and higher current flows through collector to emitter. If there are no signals in the PWM0 and PWM1 the circuit of the 12v supply voltage will have open circuit because the gate is closed and the current will not run through base to emitter. As a result, the LED turns on when the input signals(PWM0 & PWM1) of injectors are applied. When the duty cycle of the input signals increases, the two LED flash quickly or turn on continuously.     

4. Test Procedure 
- From the calculated resistor values, I have made the circuit and tested its working.
R14, R15 = 470Ω, R13, R16= 820Ω
When the duty cycle of 5v signals is increased, the two green LED flash rapidly or turn on constantly.

 - I have also created the simulation circuit from the lochmaster program before actual soldering on a board. The board, resistors, LEDs and transistors are all the same shape with real components. This simulation board is checked by my tutor and can be right.

- Then, I have made a actual injector circuit in a soldering board, such as above picture.

- Testing Available voltage and Voltage Drop

The voltage drop of LED is slightly higher than ideal voltage at 1.8v. However,all the voltage drops in the each component are similar to calculated values.
- Testing actual Amp (Ib,Ic)
Ib=4.3mA, Ic=20.03mA

5. Problems
 When I made a circuit, such as temporary circuit, the one LED do not flash. So I have checked the circuit flowing and eventually, I have found the problem which was anode and cathode direction of the LED. Then, I have changed the direction and the fail LED was flashing.
 The duty cycle value of frequency device is at around 2v and I could not read at 5v and get wrong voltage drop and available voltage. Therefore, I have changed the signal voltage with another power supply at 5v. And then, I could read correct voltage drop and available voltage.   

6. Reflection
 It was a good opportunity that have understood the electric circuit of the operation with building simple injector circuit. This circuit shows transistor's switching operation with the relationship of Base, Collector and Emitter. If the wrong resistors were chosen the circuit would not run correctly and higher resistors would make dark brightness of LED.
 If this circuit is installed in a vehicle the signals of injectors indicate the fuel injection. In addition, when the engine RPM is increased, the duty cycle of signals also goes up therefore LEDs flash rapidly and turn on continuously.