# LM2577 5V Boost Circuit does not boost voltage

I have built a 3.7 - 5V boost circuit using the LM2577-ADJ Step-Up voltage regulator.

Below is a copy of the schematic.

I have followed the datasheet (p2) and have calculated Vout as follows:

Vout = 1.23(1+R1/R2)


with values chose for R1 & R2 as:

Vout = 5.05V =1.23(1+5600/1800)


However I have constructed this circuit and with an input voltage of 3.84V (provided by a single cell LiPo) I have an output voltage of 3.56V

Below is a picture of my board layout:

Any help on this would be great, i've checked all the connections for shorts/blown components and I am a little bit stuck.

Cheers

• Compensation should be done with a series RC block instead of a single resistor, R4 (RC block is preferred as shown in the datasheet). The circuit will not be stabilized without proper compensation. Apr 26, 2017 at 14:36
• Regarding pin 1, the comp pin: in the datasheet there's an R-C to ground. Your schematic only has the resistor. I think this might upset the internal DC level on this pin making the chip think the output voltage is too high and basically switching off. Then what you see at the output is basically the current flowing through the inductor and diode. Apr 26, 2017 at 14:37
• @RohatKılıç, you should post an answer. Apr 26, 2017 at 16:00