PNP & MOSFET Based Switch: What Went Wrong?

[blackshadow]

hi eric,

i'm currently studying your circuit above. unfortunately, i could not simulate it. it says it could not open include file "LM393A.5_1_ti.mod.

by the way, can you have a brief functional analysis of your schematic? thanks again

kindly explain in detail the use of LM393 feedback resistors R7/R4 and the Vset.

i just thougt like a comparator outputs at 2 levels (+/- supply terminals) depending on the input is >1.0V or lower. then i just use that level to activate another circuit at a fixed 2.2V voltage source and on another adjustable voltage source.

if you have a simpler and easier implementation, that would be great. if not, i'll just work on this

 

[blackshadow]

hi eric,

i'm currently studying your circuit above. unfortunately, i could not simulate it. it says it could not open include file "LM393A.5_1_ti.mod.

by the way, can you have a brief functional analysis of your schematic? thanks again

kindly explain in detail the use of LM393 feedback resistors R7/R4 and the Vset.

i just thougt like a comparator outputs at 2 levels (+/- supply terminals) depending on the input is >1.0V or lower. then i just use that level to activate another circuit at a fixed 2.2V voltage source and on another adjustable voltage source.

if you have a simpler and easier implementation, that would be great. if not, i'll just work on this

i see now that the feedback resistor is for hysteresis purposes?

 

[blackshadow]

Eric, i have already figured out the circuit except the R7 (this is for hysteresis purposes?what then are the 2 thresholdfs?)and it seems to really work per simulation. So R4 makes up for the voltage divider at the base. my load would vary from about 500 ohms to 50k. instead of LM393, i'm gonna be using LM397 because i have already this component. Luckily, i have also 2n222 so i should be able to try this one..

thanks so much!

 

[ericgibbs]

Eric, i have already figured out the circuit except the R7 (this is for hysteresis purposes?what then are the 2 thresholdfs?)and it seems to really work per simulation. So R4 makes up for the voltage divider at the base. my load would vary from about 500 ohms to 50k. instead of LM393, i'm gonna be using LM397 because i have already this component. Luckily, i have also 2n222 so i should be able to try this one..

thanks so much!

hi,
The hysteresis resistor is to prevent 'oscillations' of the first LM393 output at the transition point of the threshold voltage.
If your 0V thru 2V input signal is changing 'slowly' then the LM393 output could fluctuate at the 1V threshold, as set by the SET pot.

You did not state the output load, thats why I used an emitter follower, it should be able to drive the 500R load OK.

 

[blackshadow]

Look here for lots of libs.
**broken link removed**

EDIT:
**broken link removed**

**broken link removed**

What are the files/extensions i needed to make this LM393 work in LTspice simulator?

 

[ericgibbs]

What are the files/extensions i needed to make this LM393 work in LTspice simulator?

hi,
Which manufacturers LM393 model are you using.?

You need to have .include LM393nnnn.mod text on your circuit, where nnn is the model type.

 

[blackshadow]

hi,
Which manufacturers LM393 model are you using.?

You need to have .include LM393nnnn.mod text on your circuit, where nnn is the model type.

i got it working now eric.

1 remaining question: for the VVAsource (0 to 3.5v), it seems Q2 is on its active region where we needed around 6V to output 3.5V. my challenge here is that i would like to my load to at least follow the voltage at the VVAsource. How about using FET switch for Q2? any new idea?

 

[blackshadow]

Hi Eric,

Finally, i have a working circuit which address my key issue above: VVAsource should be directly connected to the VVAload.

I made 2 key revisions from your initial design:

1. R4 is connected to the ground since the 2.2V drive simply works in this condition.
2. I operated Q2 into saturation or a Switch. This is to make my Variable Source directly connected to my load. Instead of Q2's supply tied to the VVA source, i tied it to the 5V source. This would saturate Q2 with its Vbe and Vbc > 0.7.

Do you have any technical objections or probably issue i have with this modifications?

See attachments of the schematic and the voltage output plot with VVA sweep from 0 to 3.5V.