getting negative voltage from dc supply

Thread Starter

boomhauer

Joined Jul 16, 2020
10
forgive the poor sketch but i am wondering if this will give me a negative voltage from a bench supply i am trying to piece together with parts i have lying around?

first thing i guess is would the outputs of the lm2596's be isolated from the dc input? secondly, if i connected say the 5v fixed gnd to the +variable (set to 5v) would that then give me a +5v from the fixed terminal and a -5v from gnd terminal of the variable output? if so what then would be the ground, would it be the connection between fixed ground and the variable +?

bad sketch2.png
 

ronsimpson

Joined Oct 7, 2019
811
The lm2596 is almost never used for isolation.
The lm2596 can make the 3.3V and 5V but not the 12V, or the -5V. (see circuit below)
It will not make 0-12V. Minimum voltage is 1.2V and with 12V input the max output is about 10V)
1595386835725.png
 

Thread Starter

boomhauer

Joined Jul 16, 2020
10
The lm2596 is almost never used for isolation.
The lm2596 can make the 3.3V and 5V but not the 12V, or the -5V. (see circuit below)
It will not make 0-12V. Minimum voltage is 1.2V and with 12V input the max output is about 10V)
View attachment 212761
ok i understand the "not making the 12v" but not the not making the -5v. the schematic you showed does show a -5v ?? i was using the 12v dc in purely as representational as i plan to step the 12v dc up before it gets to the terminal and out to the step down converters if that is allowed. i am just starting to do anything with electricity so i have next to zero working knowledge, only what i learn by doing it or by question. usually reading what someone else has put to paper only provides more questions for me unless it is very thorough
 

ronsimpson

Joined Oct 7, 2019
811
The circuit I showed is in the data sheet. It is not common but works.
The LM2596 is a "buck" PWM. It is used to reduce the voltage. There are "buck boost" versions that will allow you to get the effect of Buck when you need it and Boost when you need that. So 12V in to 12V out is possible. (more complicated)

How much current for each supply? 3.3V @ 2A?
 

Thread Starter

boomhauer

Joined Jul 16, 2020
10
The circuit I showed is in the data sheet. It is not common but works.
The LM2596 is a "buck" PWM. It is used to reduce the voltage. There are "buck boost" versions that will allow you to get the effect of Buck when you need it and Boost when you need that. So 12V in to 12V out is possible. (more complicated)

How much current for each supply? 3.3V @ 2A?
the lm2596's i have are adjustable i labeled as fixed since once they are connected and inside the bench top unit they will not be changed. as for current i have a total of 14.2 amps to work with. i do not currently know what current the converters output at each voltage rating except that i think it is lower than 2 amps @ 3.3v until it gets a sufficient load on it then it jumps up to about 2 amps. i did connect a little motor to one couple days ago and ran it up to almost 12v and it still wasnt pulling barely 1 amp but that just be the motor to as i do not know what its specs are was an extra from a rc car few yrs back. i have no boost converters only buck but was planning on that being a diy as well
 

Thread Starter

boomhauer

Joined Jul 16, 2020
10
i probably have enough to build the entirety of it in one circuit using ac mains but circuitry and electricity and all of this is completely new to me and just thought this would be a quick learning experience and produce something usable at the same time. i have diodes, transistors, regulators, resistors, etc. etc. but putting it all together into a finished product with the outputs i am trying to achieve i haven't a clue and when i find one i think will work there is always one part i do not have and what equates to same sometimes isnt easy to find out
 
Top