ok all I am sure this is simple but I am trying to alter a 4.5vdc car power adapter to output 3 or 3.3v however I am unable to make out the righting on the IC chip so I am hoping that someone here maybe able to help me out based on the fact that there are 3 resistors I would assume one of them controld the regulator chip output.

Thanks,
Yonu

 

Run the 4.5 volts output through two diodes in series and it should be about right. .6 volts drop across a 1N4004 with a load. Cathodes toward new circuit from plus side of power..

 

hey thanks

I will give it a shot.
In case it matters I managed to read the ic it is a
CHN 063AC K01225

thanks,
yonu

 

The chip is most likely a MC34063A. This is a old but very common buck / boost regulator.



Just look at the datasheet for the MC34063A. Formulas are not very complicated.

There are also online calculators.
http://www.nomad.ee/micros/mc34063a/

 

Run the 4.5 volts output through two diodes in series and it should be about right. .6 volts drop across a 1N4004 with a load. Cathodes toward new circuit from plus side of power..

The right way would be to change out the sensing resistor as per the datasheet.

 

The chip is most likely a MC34063A. This is a old but very common buck / boost regulator.
...

Good call, it is absolutely a 34063.

I have seen them often in car 12v stepdown adapters. And not just old ones, it is still probably the most popular IC for small cheap china gizmos that plug in a 12v cigarette lighter socket.

 

ok I had a look at the data sheet and if I understand right the sensing resistor is on pin 7
which based on that it is the circled resistor but I am confused on how to use the calculator you linked to get the new value

 

would someone mind using the pics I posted and tell me what the resistor values are I have set and worked them up from the color bands and am unable to match the values I come up with to identify each resistor to change them.

Thanks,
yonu

 

What's V in?

With just 12 volts in and 3.2 out in the calculator I get: R1=3.6k R2=5.6k (3.19V)
Nothing for Rsc but it would need a current value to calculate.

The resistors are numbered R1 and R2 on the board aren't they? Check the pins.

 

yeah on the board there is an r1, r2, and r3 that is what was confusing me and and maybe that was my issue I was assuming 13.6 as the input

Thanks,
yonu

 

ok I just started looking at the board again there is R1-R5

 

I think I have this figured out r2 and are r4 are in series totaling 3.7kohm and r3 is 1kohm

R1= 0.39ohm 5%

based on the calculator that spinnaker was kind enough to link for 4.5v I should have sense being .5ohm R1 should be 1.5kohm R2 should be 3.9kohm

so based on that should I be able to assume that R3 on the board is R1 in the datasheet and R2 and r4 on the board are R2 in the datasheet diagrams or am I way off.

Thanks,
Yonu

 

ok I am a bit confused I decided to try removing the 2.7k resister and replace it with a 760ohm to get me the close to the 1.8k that the calculator says I need however whe I connected it the output drops to 1v so I am sort of confused any advice would be great.

Thanks,
yonu

 

You are confusing us. What value do you have for R1? What value do you have for R2? And try using a capital letter at the beginning of your sentences and a period at the end. You need to put some effort into making it easier for others to help you.

 

Ok about the grammar sorry I am posting from my cell phone. The current sense resistor is 0.39ohm, R1 is 1k, and R2 is 3.7k but it is a 1k and 2.7k in series.

yonu

 

I am posting with my tablet right now and I use caps.

Did you check the data sheet? That combination would get you 5.8 V.

If you had the resistors reversed then you would get 1.6v close to what you are measuring.

 

Yes I noticed the datasheet but that is what is currently on the board. I based what R1 and R2 are in the diagrams by the values of the original resisters.

Yonu

 

R2=1.4k. R1=1k. would get 3v.