# AMS1117-3.3 over-heating and blow up way below max current

I am designing a circuit for my home automation system. To give a gist, I have a 12V 3.5A supply. I need to operate multiple loads off it. One of the Loads is a ESp12E module.

Esp12e module ----- Max current pull = 350mA. Voltage = 3.3V.

For this purpose, I am using a regulator AMS1117-3.3 Following is my circuit diagram:

My Problem is, with this connection, the AMS1117-3.3 regulator is heating up and hence blowing up. I have read the datasheet and it says "Max output current = 1A"

What can be the problem?

• It also has a maximum power dissipation rating that you seem to be exceeding. Linearly regulating 12V down to 3.3V means getting rid of a lot of excessive power. Commented Dec 12, 2016 at 11:06
• Yes, 12V to 3.3V at 500mA means dissipating nearly 45W of power Commented Dec 12, 2016 at 11:11
• @shantanu no, 4.35W. But that is more than a AMS1117-3.3 can deal with. Commented Dec 12, 2016 at 11:13
• Or a DC-DC step down regulator. These step down the voltage without wasting power as heat. Commented Dec 12, 2016 at 11:20
• @SteveG: "... without wasting as much power as heat." With efficiencies on the order of 80-90%, you can still expect a switching regulator to waste about 10-20% of the output power. Which would be about 120-240 mW in this case, a huge improvement over the linear regulator. Commented Dec 12, 2016 at 11:59

Summary: go with a buck regulator which saves power and space.

If linear regulator is still a choice, due to the huge voltage difference between input and output (12-3.3 = 8.7 V) and the current through linear regulator ( 350 mA) you would see a power dissipation of about 8.7 * 0.35 = more than 4 W!!. This huge power is dissipated as heat.

Adding a big heatsink, will help the regulator to live the huge heat dissipation. Also. Chose the linear with thermal packaging which has got good (lesser thermal resistance) thermal characteristics.

Another option is to bring down the voltage to 5 V or 4.5 V using switching regulator. Placing the linear after the switching regulator now will be dissipating lesser heat because it has to drop lesser voltage across it.

Relevant application note from TI : Google "SLVA 462"

Understanding Thermal Dissipation and Design of a Heatsink

refresher 2