Injector Circuit

Components used:

• R14 and R15= 180R (0.6W)
• R13 and R16= 390R (0.6W)
• 1x White l.e.d (30mA 1.8V)
• 1x Yellow l.e.d (30mA 1.8V)
• 2x Transistors. (C547 w64 NPN)
  

First i calculated the values for R15 and R14 the resistors that run off the L.E.Ds.

12-1.8/0.030= 340 ohms.

I used 2x 390 Ohms as it was the closest preferred value.

For the load resistors R13 and R16 i calculated them by.

5/0.030= 166.6 Ohms.

I used 2x180 Ohm resistors as it was the closest preferred value.

I calculated the resistors incorrectly and also used the incorrect ones. The circuit still worked. I needed to use the the current across the base to calculate the resistor. I used the IC max of 100mA to work out IB

Ib= IC/B. I used 100/110= 0.90mA.

4.3/0.009 = 477.7 Ohm

I could of used 2x470R

The circuit is actually two different circuits on a single circuit board. Each circuit can be used individually by having the 12V on the positive and negative rails and 5v to the required circuit. If both circuits have a 5V input both l.e.d.s will light. R15 and R14 resistors are there to protect the l.e.d and R13 and R16 are the load of the transistor. This limits the current to the base. The transistors is acting as the switch in this circuit. No l.e.d.s will light if there is no 5v input because the collector and emitter are shorted because there is no base connection. so VCE would be 10.2V with no 5V input. (12-1.8v LED). The transistor is said to be in its cut off zone. when the 5v input is connected the transistor is considored saturated The circuits can be easily switched between each other. It is called an injector circuit because it works similar to EFI circuit because the circuits can changed between each other quickly with the help of an ECU or a controlling circuit

Test procedure

Check the l.e.d.s are active when the 5v input has been connected. Check VBE is 0.7V this is when the transistor is saturated. There should be 1.8 Volts across each l.e.d. Check all drillings have been made under the resistors.

I didn't have any problems with this circuit it worked first attempt.If i was to remake the circuit in the future i would probably use jumper wires instead of stretching component legs and have all the components flat on the circuit board.