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[SOLVED] Problem with LM2576 Power Supply

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ashish.talaviya

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I have designed Power supply using LM2576-5V same as suggested in attached image. But it gives me 6V. My input is 15V and output is 6V. I have maximum input of 24V ann 1.5A, and i want output of 5V and 1A. What should i do? lm2576-5v-Test-Devresi.png
 

did you connect the diode type as given or any other diode type number?

what is your inductance value?
 

The feedback should try to stabilize it at 5V with any kind of diode or inductor although with the wrong types it could be very inefficient, especially if a slow diode is used.
Is the LM2576 from a known good supplier and definitely a '-5' version?

Brian.
 

I connect diode SS34 from PIN 2 of LM2576 to ground in reverse? (AT pin 2 i connect diode -ve and +ve is connected to ground). The name written on IC is LM2576-5.0 P+

I also have LM2576S-ADJ P+. How can i get +5V output from it?
 

I also have LM2576S-ADJ P+. How can i get +5V output from it?
Click to expand...
Adding a feedback voltage divider according to datasheet specifications.
 

ok. But can you give me solution about why i am getting output from LM2576-5.0 P+?
 

No, I can confirm that LM2576 is working correctly if wired according to the datasheet. So something most be wrong, either with the circuit layout or the components.
 

I use SS34 diode, 330uH Inductor. I attached image what i have done.20160108_174221.jpg
 

Hi,

maybe you could show us a picture of your circuit, where we can see the wiring and the parts.

Klaus

- - - Updated - - -

Hi,

Coil L1 is missing in your schematic.

Klaus
 

Sorry, But i connected 330uH inductor between pin 2 and 4.

- - - Updated - - -

Can anyone give me solution about how can i get +5V from LM2576-5.0 P+?
 

Can anyone give me solution about how can i get +5V from LM2576-5.0 P+?
Click to expand...
Already answered, I believe. The reference circuit shown in post #1 is expected to work.
 

Hi,

please check that both electrolytic capacitors are high frequency (and low ESR) capacitors, suitable for SMPS.
(Don´t use standard mains frequency electrolytic capacitors)

Again:
maybe you could show us a picture of your circuit, where we can see the wiring and the parts.

..a real picture of your circuit (or PCB layout), not the schematic.

Klaus
 

ashish.talaviya said:
Sorry, But i connected 330uH inductor between pin 2 and 4.

- - - Updated - - -

Can anyone give me solution about how can i get +5V from LM2576-5.0 P+?
Click to expand...
The output can go to 6V if you don't have any load. Try connecting 5-50 ohm resistor to output.
 

Hi,

good point.

according datasheet the leakage current is max. 2mA (as long as there is no negative output voltage).
So a 2500 Ohms resistor should do. Most probably a 10k is good enough.
Try this.

Klaus
 

The leakage current specification doesn't exactly answer the minimum load current problem. The -5 version has already an internal 4k feedback divider load. All datasheet output voltage specifications are for > 0.5 A load current.

I'm not sure if I ever used a LM2576 without load, but I remember many other buck converter chips, e.g. newer LM26xx simple switchers that work well without it.
 

On the company I work for, we have a product which over a 10 year lifespan has sold over 100,000 units. It uses a LM2576-5.
They are very reliable and absolutely fool proof. Technicians around here even cut it away from discarded boards to build their own 5 volt supplies.

The only problem we have ever experienced, related to this IC, is when our contract manufacturer purchased them from a Far East broker, and started failing.
Failure analysis by National Semi revealed counterfeit devices.
 

schmitt trigger said:
............
The only problem we have ever experienced, related to this IC, is when our contract manufacturer purchased them from a Far East broker, and started failing.
Failure analysis by National Semi revealed counterfeit devices.
Click to expand...
It baffles me when a company buys (supposedly USA) devices from a Far East supplier for a likely cheap price and is surprised that they are counterfeit. :-?
How do they think the prices got so cheap??
 

KlausST said:
Hi,

good point.


Klaus
Click to expand...

FvM said:
The leakage current specification doesn't exactly answer the minimum load current problem. The -5 version has already an internal 4k feedback divider load. All datasheet output voltage specifications are for > 0.5 A load current.

I'm not sure if I ever used a LM2576 without load, but I remember many other buck converter chips, e.g. newer LM26xx simple switchers that work well without it.
Click to expand...

My experience is similar to FvM's, the output is 5V even with no load. In fact you cannot call it a regulator if it gives higher output without a load.
My intention was to load the regulator with medium load and if the output changes significantly then it indicates a fault in the circuit and not a fault in the IC.

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crutschow said:
It baffles me when a company buys (supposedly USA) devices from a Far East supplier for a likely cheap price and is surprised that they are counterfeit. :-?
How do they think the prices got so cheap??
Click to expand...
Even counterfeit in the West is expensive. Prices in the West are very high because in the West 95% of the money goes to the salesman who has to have a private airplane and bribe the government to allow him to steal. PRICE INDICATES NOTHING.
 

My problem is solved. It's problem of Multimeter. Battery of multimeter is down, so it gave me wrong reading. I replaced new battery, now multimeter shows me +5V.
 

thank God !
it is not reading 5 as 6 in a poorly lit room :shock:
 

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