using TIP42 PNP paralleled

[boxer4]

Yeah you're right, didn't realize how much cap these things are (gosh darn these 5fF MOSFETs I'm used to... need reality check once in a while) they're in the 1E-9 range, thus measured in nF. Now you have 8 of them in parallel, so it's on the order of 1E-8 farads (I didn't include miller effect, which would basically double this). Your resistor is 1E4 ohms => RC constant of 1E-4. Looks like switch-on times on the order of .1 milliseconds, which is probably OK for automotive purposes.

 

[TheEquineFencer]

My only other question is where the 10K R3 is located, do I use just that one or do I need to have one across each M1-M8 Mosfets? ALSO NOTE that in this drawing I did not add the "S" select switches but I do plan to add them as in the drawing with the one Mosfet design. The program I'm using is a student version and will not let me use more than 50 componets doing the drawings.
Do you know which way I need to go with this, one or 8 10K resistors across the 8 Mosfets? If all is well I'll order parts on Monday. Thanks, Floyd.

 

[ericgibbs]

hi Floyd,
You make reference to a 1000uF, if you examine the pcb component printing its a 100uF.

If you use the 4N35 with a CTR of 1, then you could use a single 4K7 to the gates of the P MOSFET's, in place of the 10K0.
This will reduce the switching time slightly in the MOSFET's.

I would suggest that as your drawing program has limitations, dont put so much detail into drawing the opto's,
a simple box would be OK, likewise draw just one MOSFET configuration in detail,
the rest as boxes or just '*8' would get the job done.

Its important that you post a complete drawing so that we can check out the final circuit.

Eric

 

[TheEquineFencer]

got the 10000uF Cap from the drawing you posted for the overvoltage with the zener and 10R, I printed it out

If you look at the last post/drawing I make referance to not placing the switches on the drawing like I did with the (1) mosfet design because of componet limitaions on the program. I do plan to install a set of switches with the (8) Mosfet design, my program would not allow me that many componets. There is a 100Uf on the PCB in the picture on the actual board that is built but not on the injector side of the OPTOs.
What is the 4K7 you referance to?
Drawing with just (1) Mosfet to control injectors:
https://www.electro-tech-online.com/attachments/modified_injector_with_1_mosfets-jpg.14100/

Drawing with (8) Mosfets controling injectors(note I plan to add switches across ALL the OPTOs as did in the previous drawing):
https://www.electro-tech-online.com/attachments/o2-w-8-mosfets-jpg.14101/

I hate to say it but I think the program I'm using would count a box as a componet if it would let me add it. Is there a free program I can dowload that will let me do more? Electronics Workbench Multisim 2001 Textbook Edition is what I'm using. I'll check into getting the full version. the partial drawing is the same cropped from the original posted, https://www.electro-tech-online.com/attachments/o2-monitordriver-jpg.14051/
Yes, I can see where not having the entire drawing posted would be a bit of a pain, I'll start getting the entire prints posted, it may be a bit of a trick for me to do with being limited to 50 componets, but I'll figure out a way.
With both drawings, the (1) and the (8) mosfets contoling the injectors, the switches the theory of operation will be as follows:
System is armed when the 12V switched is closed turning the injectors ON all the time.
The LEDS light from right to left as the voltage from the O2 sensor input rises, I will leave lets say the left three OPTO switches closed, when the voltage level reaches the first OPTO with a closed switch it will cause the Mosfets to open the injector circuit. If voltages continues to rise it will still leave the injectors off, as the other two above the first will supply voltage to the Mosfets that already have 12V from when the first OPTO turned on. I'll get better at this I'm sure.
On another note, I went for a job interveiw Friday. The test given was part mechanical and part electrical. The mechanical was a small hand cranked machine I was given 10 minutes to play with then sent outside while they changed adjustments to disable it and I had to fix it, 10 minutes per problem allowed, I did the four problems in a total of 12 minutes. Then we did the Electrical, 15 minutes each allowed 5 problems given, I did it in a toatal of 18 minutes. The comment I heard one of the guys giving the test was "Rick's,
(the Department head), is not going to beleive how fast this guy did the test." When I came back in the room for the final test he asked how long I have been do electrial control wiring, I told him about a year, just what I'd learned in school and on the internet. He thought I was joking!

 

[ericgibbs]

hi,
Congrats on a good interview, hope you get the job, what will you be doing in the job?

Yes ref the 10000/1000uF, I think we both got to many '0's. its 100uF

Ref the 4K7, you recall some other posts talking about gate capacitance?

If you are now using a 4N35, you could use a 4K7 in place of the 10K0 on the
gate of the MOSFET, this will decrease the charge time of the gate cap.[improve switch on speed]

For reference only, see attached dwg, its for when I suggested a single 20Amp N MOSFET, rather than 8 P MOSFET's.

Eric

 

[TheEquineFencer]

Industrial maintenance for a Sara Lee bakery In Tarboro,NC USA.
I'm still using the 4N25s right now. You've lost me a little with this drawing. I'm to use the drawing I did with the (1) Mosfet design, see https://www.electro-tech-online.com/attachments/modified_injector_with_1_mosfets-jpg.14100/ for drawing info, but replace the FDS4935A Mosfet with a VNP20N07 Mosfet, Connect the source and drain for the VNP20N07 as you have drawn, see **broken link removed**, am I correct so far? If so looking at that drawing see https://www.electro-tech-online.com/attachments/modified_injector_with_1_mosfets-jpg.14100/ I've drawn a R3(10K resistor) from the gate to the ground coming out of the injectors that is taken back to my 12V source ground. If this is correct what else do I need to add? I like the To-220 mount a lot better also. https://www.st.com/stonline/books/pdf/docs/1607.pdf
I hope to get good at doing PLC work after the next two semesters at school. I really want to learn how to work with microprocessors so I can do things like I'm trying to do with this O2 thing and be able to do adjustmets with a laptop. The side benifit will be I can also get paid for doing it at work. The only reason I want a job now is so I can support my hobbies! It's been nice not working for the past 1 1/2 years after I got laid off, corprate buy out and shutdown, but it's about time I start back doing something besides sitting on my butt, going fishing, foxhunting, or just doing some odd jobs to put gas in the truck. It's been an interesting time though. I've yet to buy any meat from the store after getting laid off. I was given two deer, now in the freezer, 1 cow, and seven turkeys I've been eating on. A student at school shot the deer for me, he wanted the antlers, I provided the deer from the farm here. Another buddy I put some fencing up for him and got paid cash PLUS a cow,she's in the freezer too, the cow that is. The turkey farm up the road had a truck turn over and I managed to chase down the birds I've got in the freezer too. Now if someone would just turn over a produce truck I'd have it made! I was raised in the city by my parenets that were raised farming. I've met a great woman, lots of money and smarts, keeps her money, I don't get squat, but we work great togather, she's the real horse person, I just learned from her and now enjoy the farm life! She's the one that got me into Foxhunting and carriage driving, that led to playing POLO. I have to admit, POLO is almost as good as sex for excersise. She retired as Master from the Hunt we were hunting with a couple of years ago. I've led a rather interesting life after I got a divorce, I thew caution to the wind and decided to live life like there was no tommarow. If I see something I want to try or do, I go for it, nothing ventured, nothing gained. Thanks, Floyd.

 

[ericgibbs]

hi,
I see that pin9 of the LM3914 is not connected, this means the LED's will form a single 'ON' dot display, not a 'bar' graph.

The effect on the solenoids would be,,,

As the O2 level rises and say, you have Sol#3 switch selected, when the #3 LED lights the solenoids will be de-energised,,, if for some reason the O2 continued to rise then #3 LED will go OFF and the solenoids will re-energise??

If you want the LED's to display as a 'bar' insert the copper link as shown on the pcb layout,,, so as #3 comes ON with a rise in O2, it will remain ON, [solenoids all OFF] until the O2 level falls below #3.

I am not sure which mode of operation you require, but have the choice.

Eric

 

[TheEquineFencer]

As the voltage rises/O2 level going down, and it gets to the first , switch, say S-12 On drawing the injectors will cut off, if for some reason voltage rising/the O2 level falling, continues, with the switches S-11 and S-10 closed they will stay off. Then, when the O2 level rises/voltage falling, past the set point,S-12, they will fire again until the O2 level falls/Voltage rises to the S-12 switch level and the whole cycle starts over again. In theory this should happen in milliseconds if I do not have the primary fuel system calibrated correctly.

In closing I'm going to assume the drawing is correct and I will order the parts this afternoon.

 

[TheEquineFencer]

The parts are on order.