information about lm2576.

yogesh nandurkar

Prodigy 135 points

Other Parts Discussed in Thread: LM2576, LMR14050, TPS54560

i want to design dual power supply with high current rating ,i am not familiar with lm2576.

can anybody tell me how to use lm2576 negative (-5 volt) generation. please reply me i am waiting .

thanks

yogesh

over 9 years ago

0 LeonardEllis over 8 years ago

TI__Guru 71526 points

Hello Yogesh,

I have moved this to the Simple Switcher Forum where it will get the proper attention.

~Leonard

0 Frank De Stasi over 8 years ago in reply to LeonardEllis

TI__Guru 72055 points

Please see the LM2576 data sheet; figure 24. I have also attached some app notes that may be helpful.

slva059a.pdf 0044.slva317b.pdf slyt286.pdf

0 yogesh nandurkar over 8 years ago in reply to Frank De Stasi

Prodigy 135 points

actually sir i want to design power supply which can give up to 5 amp of current. i want it for load cell (+/- 5 volt )

i design it , lm2576 for + 5 volt and lm7905 for -5volt. but the thing is that , when i connect load cell to power supply load cell gives output 80mv without any input

sir pleas tell me there any problem because of lm7905 otherwise tell me suggestion.

thanks sir

yogesh

0 Frank De Stasi over 8 years ago in reply to yogesh nandurkar

TI__Guru 72055 points

It would be helpful if you could draw a block diagram or schematic for what you need to do.

If you need -5V at 5A you will need a higher current device.

0 yogesh nandurkar over 8 years ago in reply to Frank De Stasi

Prodigy 135 points

i have used center tap transformer of 12 volt 5 amp

0 Frank De Stasi over 8 years ago in reply to yogesh nandurkar

TI__Guru 72055 points

This schematic looks OK to me. I assume you have large Al. capacitors on the output of the bridge??

What is the issue you are seeing with this circuit??

0 yogesh nandurkar over 8 years ago in reply to Frank De Stasi

Prodigy 135 points

capacitor i used is 1000uF 35 V. and i am getting the output +5.06Vand -4.88V but when i connect load cell to power supply it gives output approx 88mV without input(pressure).
i dont understand why this happening
load cell specification
inpuit impedance=>405 ohm
output impedance => 350ohm.

0 Frank De Stasi over 8 years ago in reply to yogesh nandurkar

TI__Guru 72055 points

I am not sure I can answer your question about your sensor. If it is a TI device you may try to find the correct forum.

If there is an offset, maybe you need +/- supplies that are tracking and balanced.

0 yogesh nandurkar over 8 years ago in reply to Frank De Stasi

Prodigy 135 points

hi sir

if you have any idea to design +/- 5volt with high current rating up to 5amp , then suggest me .

thanks

yogesh

0 Luke Pan over 8 years ago in reply to yogesh nandurkar

TI__Intellectual 2790 points

Hi Yogesh,
You mean your load need +/-5V powersupply and the max load will be as large as 5A, right? If so, I'm afraid you need a 60V/5A device for the +5V output. TPS54560 may be more suitable. Or LMR14050 is also a recommendation if 40V voltage is enough for your system.

0 Luke Pan over 8 years ago in reply to Luke Pan

TI__Intellectual 2790 points

Also I saw LM7905 is a negative output LDO for max 1.5A output. So for the -5V/5A negative output, I'm afraid you need an negative output controller.

0 Alan Martin over 8 years ago

TI__Expert 4365 points

Hello Yogesh,

Perhaps I can provide some help here. First, if you are using a center-tapped transformer secondary then you need to tie the center tap of the transformer to the center of two output capacitors. This provides separate positive and negative dc sources for the two regulators in your application. Without this connection there isn't a midpoint ground reference for either regulator to act upon and it will not function predictably, if at all. Once that correction has been made there is a second issue that often causes issues with heavy loads connected across symmetrical supply regulators.; that of a startup issue where one or the other supply regulator fails to start up. This can be resolved by placing reverse biased Schottky diodes across each of the two supply outputs. I have illustrated both suggestions in the attached schematic. Thank you. Lets us know your progress. AlanYogesh.pdf

0 yogesh nandurkar over 8 years ago in reply to Alan Martin

Prodigy 135 points

thanks for your response,

i will try this on my circuit and let you know the result.and i have one doubt , i used 1000uf cap as a filter capacitor is there any effect of this. should i switch to 2200uf .

thanks yogesh

0 Alan Martin over 8 years ago in reply to yogesh nandurkar

TI__Expert 4365 points

The following schematic might not have attached to my earlier response. (Can't tell from my browser.)

1106.Yogesh.pdf

0 Alan Martin over 8 years ago in reply to yogesh nandurkar

TI__Expert 4365 points

This schematic using an AC input via a bridge rectifier will need a center tapped transformer to generate the independent raw +and - voltages into each rail regulator.

A better approach is to use two buck regulators, one in conventional buck configuration to create +5VDC. The second one in inverting buck-boost for the -5V rail as shown in Ap Note SNVA722B by Anston Lobo.

Each of these regulators will need a reverse biased Schottky diode placed across it's output to insure correct start-up since the end application can pull current from one rail to the opposite without conduction through the common ground.

0 Alan Martin over 8 years ago in reply to yogesh nandurkar

TI__Expert 4365 points

Consider the following approach. Refer to SNVA722B

Yogesh_Approach.pdf

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