current expansion vs overheating?!

[stoyanoff]

Greatings! I have 24V dc power supply, but my pcb is running on 3.3V. So I`m using LM317 to decrease the voltage. My pcb is draining 300mA,so the big voltage drop on LM317 causes very fast overheating. I can`t put heatsink because there is no space. So I want to try to increase the max current through LM317 in attempt to decrease the heat. https://www.ti.com/lit/ds/symlink/lm117.pdf Figure 43. Is it possible or I have try something different?
Thanks!

 

[FvM]

So I want to try to increase the max current through LM317 in attempt to decrease the heat.

Should work how?

Power dissipation is voltage drop multiply load current, about 6W in your case. Won't work without a heatsink.

Alternatively, you might think about a switched mode power supply, which has higher efficiency than linear supply.

 

[tpetar]

As FvM said in previous post you need good heatsink for 6W dissipation. LM317 can handle dissipation of 0,5-1W without heatsink, but 6W is too much. LM317 is linear regulator and have poor efficiency compared to switched mode regulators.

See this switched mode psu IC as alternative solution, which require small space and give good efficiency :

MCP16321T-330E/NG
DC-DC Step Down converter, Vin:6V-24V, Vout:3,3VDC, max 1A, Case QFN16, Price around 2eur
https://www.tme.eu/en/details/mcp16...ulators-dc-dc-circuits/microchip-technology/#

Datasheet:
https://www.tme.eu/en/Document/d3ba62e62f69b42e40d613a638f28859/mcp16321_2.pdf

Example circuit:




Best regards,
Peter

;-)