# RC switching using MOSFETS question

#### Kkein

Joined Jun 10, 2011
46
Many thanks, Jony130. Attached is screen shot of what I have done. The only question is, should enter the entire model on the "All properties" box?
What should I do with existing properties i.e BV=3.3 while the model specifies BV=30?
I also noticed that Eg=85. I have read that activation energy for silicon is 1.11 Si. Is this 0.85?
Appreciate.

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#### Kkein

Joined Jun 10, 2011
46
Jony130, it works !!! Thank heaps. One last question. Why is the voltage always 37.2V when N=77.06?

When I change N=1.5, the voltage drops to 1.2V. What is N? I thought N is emission coefficient.

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#### Jony130

Joined Feb 17, 2009
5,439
Yes, N is emission coefficient.

Vdiode = N*Vt* ln(Id/Is) so for Id = 1A ;Is = 10nA; Vt = 26mV and N = 77;

we have Vdiode = 77*26mV * ln(1A/10nA) = 2V * ln(100M) = 2V * 18.42 = 36.8V

And N is equal to 77 on purpose to model PV panel

http://www.ko4bb.com/Solar_Optimizer

#### Kkein

Joined Jun 10, 2011
46
You're a genius, Jony130. Thank heaps.

#### Kkein

Joined Jun 10, 2011
46
Hi Jony130, I just came across another problem with circuit after putting all circuits together.

The problem is, the capacitor never charge to full voltage of 37V when the circuit stage is switched ON. When I remove Q1, the capacitor charges to the full voltage. What could be the problem?

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#### Jony130

Joined Feb 17, 2009
5,439
Are you sure that this solar panel can provide 37V for 1A of a load current ?
Also why you add Q4 and D4?

PS. and IRF3713L has low drain to source breakdown voltage (30V).

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#### Kkein

Joined Jun 10, 2011
46
Jony130,
I added Q4 to switch Q1 on since Q1 is not a logic level mosfet - was trying to make a driver. D4 was probably unnecessary. Thanks for your help.

Regarding your question "37V for 1A of a load current", no I'm not sure. I have a solar panel whose Voc is 28V & Isc is about 1.05A. I intent to use it to charge capacitor in a simulation.

#### Kkein

Joined Jun 10, 2011
46
Gentlemen, I'm making progress. However, I have noticed the charging current is lower than the discharging current. I'm of the understanding that both should be the same. Why isn't this the case?

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#### Jony130

Joined Feb 17, 2009
5,439
I don't know, simulation error? Upload the simulation file.

#### Kkein

Joined Jun 10, 2011
46
Hi Jony130,

Here is the file. Thanks mate.

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#### Jony130

Joined Feb 17, 2009
5,439
I replace PV with a 20V battery and discharge current was indeed equal to 0.98A.
So everything is ok with a simulation. But look again at diagram that you have post above. Look at channel C waveform. As you can see Voc voltage reaches almost 4V. And this mean that capacitor voltage is equal to Vpv = Voc * (1 + R41/R40) = 4 * (1 + 50/10) = 4*6 = 24V