12v to 6v Buck Converter LM2675-adj producing no output voltage and getting very hot

Thread Starter

tsha2431

Joined Apr 26, 2017
5
Hi everyone,
I am trying to build a buck converter using an LM2675-ADJ. I am trying to convert from 12v to 6v. I followed the instructions in the LM2675 datasheet. The problem is I am getting only a few mV on the output and the LM2675 gets super hot fast. I have rebuilt this circuit 5 times on different boards and different layouts. I made sure my soldering is good. I just can't diagnose what I am doing wrong any help would be appreciated.

I am using the following parts:
1000ohm resistor
3900ohm resistor
1n5822 Schottky diode
100uH Inductor
2200uF Electrolytic Capacitor
1000uF Electrolytic Capacitor
 

ronv

Joined Nov 12, 2008
3,770
Hi everyone,
I am trying to build a buck converter using an LM2675-ADJ. I am trying to convert from 12v to 6v. I followed the instructions in the LM2675 datasheet. The problem is I am getting only a few mV on the output and the LM2675 gets super hot fast. I have rebuilt this circuit 5 times on different boards and different layouts. I made sure my soldering is good. I just can't diagnose what I am doing wrong any help would be appreciated.

I am using the following parts:
1000ohm resistor
3900ohm resistor
1n5822 Schottky diode
100uH Inductor
2200uF Electrolytic Capacitor
1000uF Electrolytic Capacitor
How about the Cb capacitor?
 

Thread Starter

tsha2431

Joined Apr 26, 2017
5
Okay... that's hmmm... I'll go back see if I can find the right size. What size caps would you guys suggest?
 

Thread Starter

tsha2431

Joined Apr 26, 2017
5
Okay so I change the input capacitor to 100uF electrolytic and the output to 47uF. I used the following equation as per the datasheet:
Cout = 13,300 (Vinmax / (Vout . L) where: Vinmax = 24v, Vout = 6v and L = 100.
Still the IC is just getting hot and only outputting 100mV.
 

ronv

Joined Nov 12, 2008
3,770
Okay so I change the input capacitor to 100uF electrolytic and the output to 47uF. I used the following equation as per the datasheet:
Cout = 13,300 (Vinmax / (Vout . L) where: Vinmax = 24v, Vout = 6v and L = 100.
Still the IC is just getting hot and only outputting 100mV.
Is Cb there? It is not on your list.
 

Thread Starter

tsha2431

Joined Apr 26, 2017
5
It was the diode around the wrong way. I didn't think it was wrong because the previous one I built had it that way and still worked. Wish I could delete this thread, failed project, failed post haha. Thanks for your help tho. I am learning and hopefully, one day soon can help others.
 
Top