Ignition updates to the Unofficial FAQ

There is a big part of the confusion - electrons flow from [-] to [+].

The entire "hole" thing never helped me, either. I got a lot farther when I
started thinking of where the "positives" flowed, because both vacuum tubes
(which were still common when I was learning electronics) and NPN
transistors (which are the most common now but least common originally, both
for technical reasons) use negative ground. Trying to follow electron flow
distorts the idea of the ground, while thinking of "positives" flowing from
the power supply to ground worked great. (Also the "positives" flow in the
direction of the arrow on the emitter.)

For NPN transistors, here is the simple view. The emitter is grounded and
the collector has positive voltage applied to it. The transistor doesn't
conduct because the collector-base junction is reverse biased. Now positive
voltage is applied to the base. Below about 0.7 volts on the base nothing
much happens. As 0.7 volts is approached the base-emitter junction starts
drawing current, just like any other ordinary silicon diode. The
base-emitter current causes tens to hundreds of times that much current to
flow from the collector to emitter. As the base voltage rises to about 0.8
or 0.9 volts, the base-emitter current is so high that the collector current
can't go any higher - the voltage at the collector has dropped to only
0.1-0.2 volts, and the entire supply voltage (like the 12V battery) is
across whatever load is between the power supply and the collector. In the
ignition circuit, the collector has grounded the primary of the coil. This
condition is called "saturation" because increasing the base current doesn't
do anything to the collector any more.

It is important in switching circuits like the ignition to saturate the
transistor. If the collector voltage doesn't go very near ground, the
transistor has to dissipate the current times whatever voltage is left. If
the voltage is only twice the saturation voltage (say, 0.3 instead of 0.15)
the transistor has to dissipate twice the power.

Mike

 

Most materials have an electron flow, which goes from negative to
positive. I've heard that some materials can have a proton flow. Both
may exist in a vacuum.

Current flow arrows on diagrams go from positive to negative.

Bipolar transistors are current amplifiers. When a current flows
through the base-emitter diode junction, a stronger current is allowed
to flow from the collector to the emitter. The C-E junction is .2 to .4
volts when the B-E junction is saturated (~.65 V). The current gain for
a power transistor is usually 10 to 100. Darlington pairs have that
gain squared. Gains are not at all consistent so they're usually
specified as a range.

MOSFETs are tiny voltage controlled amplifiers. Absolutely zero static
current is required to turn them on or off; just the capacitance
current. Because of their infinite current gain, millions may be
paralleled on a single chip to satisfy any current load. Their voltage
gain is very low - a typical gate threshold voltage is 4V and a typical
gate saturation voltage is 10V. There's no voltage drop between the
source and drain, only resistance. High voltage capability makes each
MOSFET junction larger and dramatically increases resistance.

IGBTs are similar to bipolar transistors but with an insulated gate like
a MOSFET. They have the high voltage capacity of bipolars but need no
driving current like a MOSFET. They're very slow so they're usually
limited to controlling industrial motors. (Honda hybrid cars use them
for their motors.)

 

Most materials have an electron flow, which goes from negative to
positive. I've heard that some materials can have a proton flow. Both
may exist in a vacuum.

Current flow arrows on diagrams go from positive to negative.

Bipolar transistors are current amplifiers. When a current flows
through the base-emitter diode junction, a stronger current is allowed
to flow from the collector to the emitter. The C-E junction is .2 to .4
volts when the B-E junction is saturated (~.65 V). The current gain for
a power transistor is usually 10 to 100. Darlington pairs have that
gain squared. Gains are not at all consistent so they're usually
specified as a range.

MOSFETs are tiny voltage controlled amplifiers. Absolutely zero static
current is required to turn them on or off; just the capacitance
current. Because of their infinite current gain, millions may be
paralleled on a single chip to satisfy any current load. Their voltage
gain is very low - a typical gate threshold voltage is 4V and a typical
gate saturation voltage is 10V. There's no voltage drop between the
source and drain, only resistance. High voltage capability makes each
MOSFET junction larger and dramatically increases resistance.

IGBTs are similar to bipolar transistors but with an insulated gate like
a MOSFET. They have the high voltage capacity of bipolars but need no
driving current like a MOSFET. They're very slow so they're usually
limited to controlling industrial motors. (Honda hybrid cars use them
for their motors.)

 

So then my diagrams are correct. I assumed the base electrode to act as the
switch, turning power on and off between the collector and the emitter.

Thanks.

 

So then my diagrams are correct. I assumed the base electrode to act as the
switch, turning power on and off between the collector and the emitter.

Thanks.

 

don't get no proton flow unless you're into nuclear chemistry. in
semiconductors, conduction is by way of negative electrons & positive
"holes". you /can/ have [positive] ions move in the semiconductor
lattice, but they are not a part of the primary conduction mechanism &
result in mass transport & therefore degradation of the semiconductor -
they are not a proton thing.

 

don't get no proton flow unless you're into nuclear chemistry. in
semiconductors, conduction is by way of negative electrons & positive
"holes". you /can/ have [positive] ions move in the semiconductor
lattice, but they are not a part of the primary conduction mechanism &
result in mass transport & therefore degradation of the semiconductor -
they are not a proton thing.

 

think of a Y water pipe.One arm of the Y is smaller than the other.But the
total water flow thru the bottom of the Y divides and part passes thru the
left arm and part thru the right arm.You can control how much water passes
thru the right arm by adjusting the flow thru the left arm.(but the water
pipe does not have any current gain)

Just think of a vacuum tube;the cathode(negative terminal) is heated so it
will emit *electrons*,which are attracted to the positively charged anode
plate,thus;ELECTRON FLOW,from negative to positive.

 

think of a Y water pipe.One arm of the Y is smaller than the other.But the
total water flow thru the bottom of the Y divides and part passes thru the
left arm and part thru the right arm.You can control how much water passes
thru the right arm by adjusting the flow thru the left arm.(but the water
pipe does not have any current gain)

Just think of a vacuum tube;the cathode(negative terminal) is heated so it
will emit *electrons*,which are attracted to the positively charged anode
plate,thus;ELECTRON FLOW,from negative to positive.

 

So then my drawings are NOT correct. I need to show the emitter (closest to
the coil) "switched off", and not the collector (farthest from the coil).
Right? Or does it matter since the effect is the same?

 

So then my drawings are NOT correct. I need to show the emitter (closest to
the coil) "switched off", and not the collector (farthest from the coil).
Right? Or does it matter since the effect is the same?

 

For a NPN transistor,the collector should go to the coil,and the emitter to
ground. The other end of the coil goes to +12V.
The internal diode shunts the back EMF around the transistor to
ground,protecting the transistor.


I just looked at your schematic,and it appears correct.except that terminal
3 of the Igniter module does not go straight to the Darlington base,it goes
to the IC that controls the Darlington.You need a rectangle indicating the
control IC between the Pin 3 and the Darlington base.Pin 1(tach drive)
probably goes to the control IC,too,certainly not to ground,Pin 4.

(the emitter of the Darlington probably goes to the control IC,too,then
thru a small value resistor[<1 ohm] for current monitoring by the IC,then
to ground.)

 

For a NPN transistor,the collector should go to the coil,and the emitter to
ground. The other end of the coil goes to +12V.
The internal diode shunts the back EMF around the transistor to
ground,protecting the transistor.


I just looked at your schematic,and it appears correct.except that terminal
3 of the Igniter module does not go straight to the Darlington base,it goes
to the IC that controls the Darlington.You need a rectangle indicating the
control IC between the Pin 3 and the Darlington base.Pin 1(tach drive)
probably goes to the control IC,too,certainly not to ground,Pin 4.

(the emitter of the Darlington probably goes to the control IC,too,then
thru a small value resistor[<1 ohm] for current monitoring by the IC,then
to ground.)

 

The emitter is the neutral part of it, the part the collector gets switched
to.

Maybe the easiest way to think of it is as a relay, where the emitter is one
end of the winding and one of the contacts. The base is the other end of the
winding and the collector is the other normally open contact. When current
is run through the "winding" (from the base to the emitter) the collector
closes the circuit to the emitter.

There are a few technical details like polarity (the collector and base both
have to be positive with respect to the emitter) and the base resistance (so
low the current has to be limited by external resistance), but the operation
in an ignitor is just like a very fast relay. In other circuits it isn't
used as a relay, and the collector current is varied more proportionately to
the base current.

Mike

 

The emitter is the neutral part of it, the part the collector gets switched
to.

Maybe the easiest way to think of it is as a relay, where the emitter is one
end of the winding and one of the contacts. The base is the other end of the
winding and the collector is the other normally open contact. When current
is run through the "winding" (from the base to the emitter) the collector
closes the circuit to the emitter.

There are a few technical details like polarity (the collector and base both
have to be positive with respect to the emitter) and the base resistance (so
low the current has to be limited by external resistance), but the operation
in an ignitor is just like a very fast relay. In other circuits it isn't
used as a relay, and the collector current is varied more proportionately to
the base current.

Mike

 

More information here than I've gotten yet. Thanks.

 

More information here than I've gotten yet. Thanks.

 

Something additional I thought of after I sent the last post(sorry!);
The ECU does not ground the igniter module.It only sends a signal (to the
control IC inside the igniter)for the Darlington to ground the coil.If the
ECU were to be the ground for the igniter,that would mean that the entire
coil current(several amps) would have to travel through the long wire from
igniter to ECU,and the ECU itself would have to switch that high current to
ground,which is the purpose of the igniter.

 

Something additional I thought of after I sent the last post(sorry!);
The ECU does not ground the igniter module.It only sends a signal (to the
control IC inside the igniter)for the Darlington to ground the coil.If the
ECU were to be the ground for the igniter,that would mean that the entire
coil current(several amps) would have to travel through the long wire from
igniter to ECU,and the ECU itself would have to switch that high current to
ground,which is the purpose of the igniter.

 

Then how do you explain this?
http://www.tegger.com/hondafaq/misc/rov-ign.jpg
Look a the text immediately below the title.

Then I'm still looking for a definitive answer.