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Can I replace the Murata OKI-78SR-5/1.5-W36-C regulator with an L7805CV?

Saleh Ramadan
 

Hi all,

For some reason the 5v regulator on my maxpcb2 board malfunctioned, now when I power up the thing, the motors go online for a maximum of a minute, then the Teensy onboard will shut down due to massive overheating.

I know it is the 5v regulator because before it was causing some issues where the whole system won't start so I thought it was a soldering issue, then it worked fine for a while, until last day it just started to cause that behavior.

So with the current lovely state of the world now I don't think I'll be able to get any replacement soon... So I found an old regulator I have L7805CV and I am wondering if I can replace that non-functioning with the one I found...

Based on its data sheet, it will take anywhere from 7v to 35v, and output 5v... so it would be fine I use this one right?

Thanks for the help!
Regards

Saleh Ramadan
 

Howard Dutton
 

The L7805 will create a large amount of heat.

The more current needed from the 5V output the more heat and it'll be running stuff (Teensy, WeMos D1, SHC, etc.)  The heat is also proportional to the voltage drop required so input at 12V might be possible but I suspect 24V would be a problem.  Any heat-sinking added will help.  Also... the L7805 needs capacitors in close proximity (see the datasheet) which might be a problem.

Saleh Ramadan
 

So there is no other replacement other than the same damaged regulator?

Regards

On Wed, Mar 18, 2020, 20:12 Howard Dutton <hjd1964@...> wrote:
The L7805 will create a large amount of heat.

The more current needed from the 5V output the more heat and it'll be running stuff (Teensy, WeMos D1, SHC, etc.)  The heat is also proportional to the voltage drop required so input at 12V might be possible but I suspect 24V would be a problem.  Any heat-sinking added will help.  Also... the L7805 needs capacitors in close proximity (see the datasheet) which might be a problem.

simpsonj@...
 

You could put the 7805 and the associated caps on a small, separate board -- perhaps just a heatsink mounted remotely -- and run leads back to the pads where the old regular is mounted on a temporary basis.  The 7805 is going to dissipate the heat generated by the voltage drop (volts drop x amps through it) whereas the OKI device is a switching regulator that is much more efficient.

But if you can handle the heat in some why, a 7805 would work.

Regards
Jim Simpson

Jerry
 

You could solder some surface mount MLCCs right at the solder pads. 1008 or 0806 sizes would work fine. 

-Jerry

On Mar 19, 2020, at 10:10 AM, simpsonj via Groups.Io <simpsonj@...> wrote:

You could put the 7805 and the associated caps on a small, separate board -- perhaps just a heatsink mounted remotely -- and run leads back to the pads where the old regular is mounted on a temporary basis.  The 7805 is going to dissipate the heat generated by the voltage drop (volts drop x amps through it) whereas the OKI device is a switching regulator that is much more efficient.

But if you can handle the heat in some why, a 7805 would work.

Regards
Jim Simpson

Saleh Ramadan
 

I guess I got to do that and make the control box a bit ugly with a 5V regulator tumor stuck to its outer cover for a while... I found a cheaper option to get the burnt OKI from ebay, will see if it will get delivered or not..

Thanks all!

Saleh Ramadan


On Thu, Mar 19, 2020 at 8:45 PM Jerry <jerry.biehler@...> wrote:
You could solder some surface mount MLCCs right at the solder pads. 1008 or 0806 sizes would work fine. 

-Jerry

On Mar 19, 2020, at 10:10 AM, simpsonj via Groups.Io <simpsonj=verizon.net@groups.io> wrote:

You could put the 7805 and the associated caps on a small, separate board -- perhaps just a heatsink mounted remotely -- and run leads back to the pads where the old regular is mounted on a temporary basis.  The 7805 is going to dissipate the heat generated by the voltage drop (volts drop x amps through it) whereas the OKI device is a switching regulator that is much more efficient.

But if you can handle the heat in some why, a 7805 would work.

Regards
Jim Simpson

George Cushing
 

You in the States Saleh? Things seem to be moving again in China.

These are very similar (use the same IC) for a $1.16. Power Supply Module

These are $7 for 10. Adjustable Buck Converter



Tong
 

I have used L7805CV to work properly, the radiator is required. If you need to use GPS, the current may not be enough and the GPS will not work.