Mutiplexing Opto/Fet, Circuit provided.

Thread Starter

quant

Joined May 21, 2009
114
Hi,
Thanks again for your help. The budget is not important at all I just need it to work properly.
The purpose is to adopt my earlier circuit to a Matrix of Sols. whereby an Arduino will feed the Rows and a 4017 or 595 will power the columns.
 

Thread Starter

quant

Joined May 21, 2009
114
Hello sgntWookie,

Thank you so very much. You have been a GREAT help and I sure appreciate it.

I'll go working on it right away!

cheers
 

SgtWookie

Joined Jul 17, 2007
22,230
Sadly, you are not even close.

Why is Q3 upside-down? I have already shown you many times that P-channel MOSFETs should normally be displayed with the source terminal towards the top of the schematic, which is also normally towards the most positive voltage side of the schematic.

Also, inputs should be towards the left side of the schematic, with outputs towards the right side of the schematic.

Take another good, long look at the schematic I drew. You will see that my schematic is consistent with those two basic guidelines:
1) More positive voltage rails are nearer the top of the schematic, more negative towards the bottom.
2) Inputs from the left side, outputs towards the right side - where possible.

As far as the gate driver configuration - look back at what I posted on the 2nd page of this thread.

See if you can figure out how to use a similar configuration for the P-channel MOSFETs.

I already have the 3.3k gate pull-down/pull-up resistors in the schematic I most recently posted.
 

Thread Starter

quant

Joined May 21, 2009
114
Why is Q3 upside-down? I have already shown you many times that P-channel MOSFETs should normally be displayed with the source terminal towards the top of the schematic, which is also normally towards the most positive voltage side of the schematic.
I used the PCB wizard Library and that's how it shows a PMosfet!!!
Q3 is supposed to be an NMosfet?!

 

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SgtWookie

Joined Jul 17, 2007
22,230
I used the PCB wizard Library and that's how it shows a PMosfet!!!
OK.
That is how P-channel MOSFETs are typically shown in a library, or on a datasheet.

However, when you use them in a schematic diagram, it is much easier to understand the schematic if you have the source terminal of the P-ch MOSFET towards the top of the schematic, which is consistent with the general guidelines that I posted above. Also, since the gate is the control input to the MOSFET, it is most consistent to have the gate of the MOSFET towards the left of the schematic.
Q3 is supposed to be an NMosfet?!
No, it's supposed to be a P-channel MOSFET. However, since you have it shown with the source terminal down, you became confused and connected the source terminal to ground. It will not work like that.
 

SgtWookie

Joined Jul 17, 2007
22,230
Should I change(swap) Q3 and Q2? Since Q3 is switching Positive and Q2 the Earth?
Right now, you have both Q2 and Q3's source terminals connected to earth (ground).

Flip Q3 around (rotate 180° and mirror) so that the source is up, drain is down, gate is left.

If your software does not allow you to do that, you need to find a different software that will allow it.
 

Thread Starter

quant

Joined May 21, 2009
114
OK, considering that the Q3 is PMosfet and Q2 is NMosfet, is the circuit now correct? Just for a single Sol. circuit. I'm trying to get just one Sol. working utilizing 2 Fets like a 1x1 Matrix, to help me better understand it first and then to expand the Matrix.
 

Thread Starter

quant

Joined May 21, 2009
114
Right now, you have both Q2 and Q3's source terminals connected to earth (ground).

Flip Q3 around (rotate 180° and mirror) so that the source is up, drain is down, gate is left.

If your software does not allow you to do that, you need to find a different software that will allow it.
Isn't Q3 Source connected to 24V?
Considering the pins in both Fets as Center 1(Gate) above 2(Source) and below 3(Drain)...
 

SgtWookie

Joined Jul 17, 2007
22,230
OK, considering that the Q3 is PMosfet and Q2 is NMosfet, is the circuit now correct? Just for a single Sol. circuit.
No, it is not.

Flip Q3 around, and connect the source terminal to +24V instead of ground.

The resistor values you are using are not correct.
I'm trying to get just one Sol. working utilizing 2 Fets like a 1x1 Matrix, to help me better understand it first and then to expand the Matrix.
That is a good idea.

Once you get the individual "building blocks" of the circuit properly assembled, you can proceed at a much faster pace.
 

Thread Starter

quant

Joined May 21, 2009
114
Thanks, My typo, R2 is 10K.
Isn't Q3 Source connected to 24V?
Considering the pins in both Fets as Center 1(Gate) above 2(Source) and below 3(Drain)...
 

SgtWookie

Joined Jul 17, 2007
22,230
Still wrong.

OK, here's a big hint - there are only five basic functional blocks that you have to deal with.
1) The high side current control.
2) The low side current control.
3) The solenoids and their reverse-EMF suppression diodes.
4) The high side gate drivers.
5) The low side gate drivers.

They are all right here:



You just need to re-create each functional block in your schematic capture software, and copy/connect them as I have show you in the last matrix schematic post that I made.
[eta]
As far as the Zener diodes go, you really only need 10v Zeners. I used 12v Zeners to help the gates to charge more quickly.
 

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SgtWookie

Joined Jul 17, 2007
22,230
Oh, I see that you're adding labels to ground symbols, calling them 5v ground and 24v ground.
Don't do that. Ground is considered to be 0v.

Now if your software provides for it, you could use two different ground symbols, one for the logic level side, and one for the power side. But don't label the grounds as 5 and 24, or you will rapidly get confused.
 
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