Hello, I hope someone can help me.
I am trying to simulate a circuit involving the MC34063 using LTSpice. It's a simple 12V -> 5V DC-DC converter.
I downloaded the model (attached) for the MC34063 so that I could use it in LTSpice. The problem right now is I expect 5V output but I get 10.35V. I am a newbie and I tried as much as i can but I seems like I cant solve the issue...... I will be great if anyone can please help me. Thank you.

 

Hi ellen,
Welcome to AAC.
Using your asc file this is what I see, is it the correct circuit?
E

 

Hi ellen,
Welcome to AAC.
Using your asc file this is what I see, is it the correct circuit?
E
View attachment 357597

Yes it is the correct circuit of what i had

 

Hi ell,
I am checking the MC34063 model using the datasheet circuit, it is not working.
I suspect the lib model, I will keep checking.

Who created the model?
E

 

Hi ell,
I am checking the MC34063 model using the datasheet circuit, it is not working.
I suspect the lib model, I will keep checking.

Who created the model?
E

Hi erick

i got it from this forum below link...

https://forum.allaboutcircuits.com/threads/dc-boost-regulator-mc34063-circuit.100648/

 

hi ell,
I have recreated the model using sub file, but I cannot get the 5V example circuit from the datasheet to work.
I will get that zip link and retry from there.

Will post back later.
E

 

Hello,

It looks like that the timing capacitor is connected wrongly:


Move the ground connection of C1 in your schematic to the other side.

Bertus

 

hi ell @bertus
I did try that pin reversal 4 & 5 earlier, but still not working.
Also tried using MC34 models from two other sources, all give incorrect results.

One version gave me the same 10V as the TS's version.

E

Added Header clip from the two models, lib and sub

* This model is included in the ICAP/4 demo free downloadable software.
* It's very similar to the model in Hymovitz.lib. The vt threshholds
* are different and the model here uses net 90 instead of 0.
.SUBCKT MC34063 swc swe ct 90 2 vdd isns drc
* SW-col SW-em Ct gnd cinv vdd isns drive col




.SUBCKT mc34063 csw esw ct comm fb vcc ipk cdr

* csw = switch BJT collector, esw = switch BJT emitter ct = timing capacitor, comm = common
* fb = feedback control, vcc = power in, ipk = peak limiting, cdr = driver BJT collector
* pin numbers match order of inputs above.

 

hi ell @bertus
I did try that pin reversal 4 & 5 earlier, but still not working.
Also tried using MC34 models from two other sources, all give incorrect results.

One version gave me the same 10V as the TS's version.

E

Added Header clip from the two models, lib and sub

* This model is included in the ICAP/4 demo free downloadable software.
* It's very similar to the model in Hymovitz.lib. The vt threshholds
* are different and the model here uses net 90 instead of 0.
.SUBCKT MC34063 swc swe ct 90 2 vdd isns drc
* SW-col SW-em Ct gnd cinv vdd isns drive col




.SUBCKT mc34063 csw esw ct comm fb vcc ipk cdr

* csw = switch BJT collector, esw = switch BJT emitter ct = timing capacitor, comm = common
* fb = feedback control, vcc = power in, ipk = peak limiting, cdr = driver BJT collector
* pin numbers match order of inputs above.

Hello erick

Thank you so much for trying to help. I've been trying as well since now but its still not working.
I am not too familiar with what you have posted, it seems like it is content of .sub file. Do you wish me to edit the .sub file for MC34063?

 

Hi ell,
I guess you know that you can create a model by using *.sub, *.lib, *.net file?

I have tried these with files no success

Perhaps fellow member @eetech00 may have a better idea.
E

 

Hello,

I modified the circuit according to the datasheet.

It looks like the fb voltage is about 2.6 Volts.
The value of C1 is large, but changing it to the 470p of the datasheet results in the same picture.

Bertus

 

Hi ell,
I guess you know that you can create a model by using *.sub, *.lib, *.net file?

I have tried these with files no success

Perhaps fellow member @eetech00 may have a better idea.
E

Hi eric,

i've modified circuits and added output capacitor, which made some good progress as below, currently getting 5v output and v(fb) = 1.25v. thank you for helping me !

 

Hello,

I modified the circuit according to the datasheet.
View attachment 357607
It looks like the fb voltage is about 2.6 Volts.
The value of C1 is large, but changing it to the 470p of the datasheet results in the same picture.

Bertus

hello bertus,

I've just tried adding output capacitor and it seems like it fixed the issue I think, Ive used 100nF capacitor. Do you think it is fixed?

 

hi ell,
Post your latest files and I will give it a try.
E

 

hi ell,
Post your latest files and I will give it a try.
E

Hi eric

Here it is, tho the output v is a bit noisy

 

Here's a corrected version of the circuit with new model file.

 

Using TS's model: