Have 24V need 5V 0.1A. Works fine with 78L05 (right size) but gets too hot. Smallest cool alternative ?

[OSLO]

Powering Tinysine TSA6179 miniature Bluetooth module.

 

[adason]

0.1A can not make 78L05 hot. Have you measured actual current? Have you tried putting heatsink on it?

 

[rayma]

He has 19VDC across it, so there's 1.9W dissipation, which is rather too high.
Even a TO-220 regulator should have a heat sink in this case.
Or use a dropping resistor and decoupling capacitor ahead of it.

 

[richb]

If you don't mind a bit of switching, a buck converter module:

https://www.amazon.co.uk/Converter-3-2V-40V-1-25V-35V-Adjustable-Regulator/dp/B07K2D1GJB

 

[Mooly]

Use a series resistor or Zener to take some of the excess voltage out of the equation. Be sure to decouple the 78L05 input (and output) pin to ground correctly.

 

[NareshBrd]

100E 2W drop resistor to drop input to about 9V...24 is too much for 7805.
Change value if needed, the regulator should get 7.5 to 9 V input.
And use a heat sink...or attach to case, use case as heat sink. use isolation to ground if needed.

Should work, provided the BT module is less than 500mA load.

 

[NareshBrd]

There seem to be two threads with same poster and same title...
I just posted on the other thread, put a drop resistor....

Mods?

 

[norb]

Search for "5V switching regulator" and get one, but not toooo cheap.

 

[Mooly]

Let me have a look...

 

[Mooly]

Sorted 🙂

 

[NareshBrd]

Thanks Mooly!

 

[OSLO]

Sorted 🙂

Thanks. Probably my fault, sorry

 

[OSLO]

I just posted on the other thread, put a drop resistor....

Mods?

How ?

 

[OSLO]

I need something super miniature (like a 3-pin chip). Will B2405S or RS7805 fare better ?

 

[NareshBrd]

+24 -> 100E resistor -> input pin of 7805.
That means in series.
Simple.

 

[Mooly]

A 7805 will be better if you are near the dissipation limits of the L version. It's a bigger package and can dissipate more heat. If you are close to the 100ma limit for the L type then you should do this anyway.

 

[adason]

How about lm317, and make it adjustable.

 

[OSLO]

+24 -> 100E resistor -> input pin of 7805.
That means in series.
Simple.

Is 100 ohm 1/4 w enough ?

 

[OSLO]

A 7805 will be better if you are near the dissipation limits of the L version. It's a bigger package and can dissipate more heat. If you are close to the 100ma limit for the L type then you should do this anyway.

How about 78M05 ?

 

[indra1]

I need something super miniature ...

For 1.9W dissipation, super miniature = super hot, bigger = not so hot, heatsink = reliability.