RV 4145 A LTSpice Model

[Ekazeera]

Hi, I am new to LTSpice and currently having a lot of fun learning from the tutorials.
I am currently working on a project that involves creating a model for the RV4145 which is a Low Power Ground Fault Interrupter.
I have attached the datasheet.
It is presented in two schematics;

1. The Functional Block diagram

2.The Actual Schematic based on the transistors.

One of the decisions I had to make was whether to go with the functional block, I decided to go with the transistors schematic.
(Was this is a better decision)?

However, I am now stuck as to whether I should leave the transistors as generic or use modify them ( I realize they are not generic in the picture)

If so how can I do that given the information I have from the datasheet?

Please help me with the direction of this simulation as I am stuck.

Thank you.

 

[ronsimpson]

If I was going to make this part:
Zeners = 6.8V or 6.2V from SPICE. (or you can make a copy of the 6.2V zener, rename it, change the voltage to 6.5) (use a SPICE 6.5 voltage source, if you do that then you will not need a supply on the "+Vs pin".)
The op-amp = (supply > 26V and speed = 1.8mhz) So try LT6013.
Diodes 1N4148.
This will probably be closer than using generic transistors.

 

[alec_t]

It would be interesting (to me, at least ) if you could build the model both ways and compare their performance.

 

[ronsimpson]

if you could build the model both ways and compare their performance.

We really don't know what transistors are used. Probably 2 or 3 different types. Could easy be something that you can not get from a store. There is no reason for them to use a 2N2222a. They can make what they want.

I would use a 6.5V Zener not a back wards transistor because it might take a while to find good transistor.
When I designed ICs, I could make a op-amp from transistors but .... There is a big book of parts. You just turn to the op-amp chapter, choose a part that is a little faster than a 741. There is R-R options. The point is that you pick a part that works and has been tested in many products. Very likely the "op-amps" are the same as in other products from the same company. Re-invent the wheel. At the end the computer can hand you a transistor level print out of what you built, but who cares. You just want a 1.8mhz amp that is stable and has a certain offset and open loop gain. (and input current) I don't care how many transistors.

 

[Ekazeera]

It would be interesting (to me, at least ) if you could build the model both ways and compare their performance.

That is actually what I intend to do. I understand that they are many possibilities. And judging from the ambiguity of the datasheet, my best bate is to start with the functional block diagram type.

 

[Ekazeera]

If I was going to make this part:
Zeners = 6.8V or 6.2V from SPICE. (or you can make a copy of the 6.2V zener, rename it, change the voltage to 6.5) (use a SPICE 6.5 voltage source, if you do that then you will not need a supply on the "+Vs pin".)
The op-amp = (supply > 26V and speed = 1.8mhz) So try LT6013.
Diodes 1N4148.
This will probably be closer than using generic transistors.

How do you know the frequency requirement of the op-amp is 1.8Mhz?

 

[ronsimpson]

How do you know the frequency requirement of the op-amp is 1.8Mhz?

Data sheet.
There is a frequency where the maximum gain is one. Typ=1.8mhz Min=1.0 (from my bad memory)

 

[Ekazeera]

I see it. Thank you.

Data sheet.
There is a frequency where the maximum gain is one. Typ=1.8mhz Min=1.0 (from my bad memory)

 

[Ekazeera]

How about the two comparators, should I just use ideal op-amps for those ?

 

[ronsimpson]

How about the two comparators

I think Q15 and Q16 are the two comparators.

Pin 7 is the output of the op-amp and the input to the comparators.
Q17, 18, 19, 20 are the Zeners.
If pin 7 goes too high Q15 turns on. (pulls pin 5 high)
If pin 7 goes too low Q16 turns on. (pulls pin 5 high)
I would use two transistors. (2n2222a, 2n2907)

I erased some parts that do not count in this talk.

 

[eTech]

How about the two comparators, should I just use ideal op-amps for those ?

Hi

It shouldn’t be too difficult to finish the transistor model.
If you can wait a day or two.

eT

 

[Ekazeera]

I can absolutely wait.
I have actually also created the functional schematic but running into issues as to how to incorporate the necessary zener voltages.

 

[eTech]

I can absolutely wait.
I have actually also created the functional schematic but running into issues as to how to incorporate the necessary zener voltages.

See Attached Functional Schematic.

I didn't test completely. I'll leave that up to you. ;-)
Remember that this is a representative model so can't expect it to work the same way as the actual part.

Regarding the Transistor version. There is one being tested and available for download at the LTspice Yahoo Group.

eT

 

[ronsimpson]

I removed U2, U3.
Two op-amps will not be happy with their outputs shorted together.
Used two transistors just like in the IC.
U1 added R5 450 ohms to make the output more like the IC.
Added 200 ohms to the voltage source. Should not direct drive a Zener with a voltage source.
I did not try it. Did not look close.