Linear power suppy schematic help

Thread Starter

Teklucifer

Joined May 11, 2016
5
Thanks for the reply @ronv ,

I couldn't comprehend what you meant by
The same is true of the current limit. It will only reduce the voltage to 1.2 volts so if the output is shorted the current will still be pretty high. Is this okay
Are you talking about my circuit or @crutschow 's, How will it get shorted I still don't understand.

Your voltage is to high for the LM1084. When you add filter capacitors to the bridge rectifier the voltage will be somewhere around 33 volts. The maximum voltage from input to output is 29 volts.
So, now I go back to the LM338? Isn't there something much better with a lower dropout voltage than the lm338?

Regards,

Teklucifer
 

ronv

Joined Nov 12, 2008
3,770
Thanks for the reply @ronv ,

I couldn't comprehend what you meant by

Are you talking about my circuit or @crutschow 's, How will it get shorted I still don't understand.
Sorry, I thought maybe you were building this for a bench supply for different projects, but I bet what you want is a battery charger???
What I was saying is that the power supply IC's like the 338 can only adjust down to 1.2 volts. The do not go down to zero. But if you are making a charger you don't care because the voltage will always be higher.
If it is a charger use this one:

http://forum.allaboutcircuits.com/threads/linear-power-suppy-schematic-help.124014/#post-998955
So, now I go back to the LM338? Isn't there something much better with a lower dropout voltage than the lm338?
You have more than enough voltage so you don't need to worry about the drop out voltage as the regulator will always be dropping over 15 volts.


Regards,

Teklucifer[/QUOTE]
 

Giorgio Biso

Joined Mar 25, 2016
2
[my two cents] In the schematic posted by Analog Kid - as he noticed - there are some component values that don't fit with your starting specifications. I focused my attention to working voltage value of electrolytic capacitors: if you need a PSU with about 24 volt DC output, you should use C1 and C3 with a working voltage of at least 35 Volt. Do not economize on working voltage of capacitors. This Wikipedia's paragraph gives a good explanation: https://en.wikipedia.org/wiki/Electrolytic_capacitor#Rated_and_category_voltage

I apologize for my lack of scientific elements and proper math, but my personal rule (when I build power supplies) to avoid dense, bad smelling clouds of blue smoke is: Capacitor Working Voltage >= PSU Max Voltage * 1.4
 
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