Current limiting circuit for dynamic load

Status
Not open for further replies.
H

HagenK

Junior Member level 1
Joined
Aug 10, 2014
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Visit site
Activity points
98
So I have this 9V 2.5A power supply and a flash unit which needs 6V. I use LM7806 to drop voltage, but when the flash is charging up it overload regulator, thus further dropping voltage to megger 2.5V. I think I need to somehow limit max current draw to 1.5A. Surprisingly I couldn't find a solution in google, so maybe you guys can help me out?
 

7806 is not the best LDO to use here.

edit**
Reason? LDO will drop 2.5V at 1.5A at 85'C , which means you need 8.5 min anyway but chances are your load demands more than 1.5 and that's causing shutdown on starting.
Power dissipation (9-6V)*1.5A= 4.5W is a big problem
A heatsink will improve overtemp condition, but not enough. if overloaded. thus use a 1.5A PTC in front is a bandaid fix.

A better solution is use a better adjustable LDO with 0.5 Dropout and lose 2.5V*1.5A=3.75W in a power resistor or 3 power diodes.

The best solution is a 99% efficient Buck regulator which can output >3.5A @6V = 21W from 9V*3,5A = 22.5W


- - - Updated - - -

It may be possible to bypass LDO with a Pch FET with a heatsink
Using LDO drain current to bias Vgs=-1V (8V)

e.g. https://www.digikey.com/product-detail/en/STD30PF03LT4/497-3158-1-ND/654490

Or better use a suitable 3A 6V LDO with 0.8V dropout @3A but still needs heatsink
https://www.digikey.com/product-sea...=0&page=1&quantity=0&ptm=0&fid=0&pageSize=500
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…