Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Behaviour of the LM2577 step up regulator.

Status
Not open for further replies.
A

arbj2

Full Member level 3
Joined
Apr 10, 2012
Messages
166
Helped
10
Reputation
20
Reaction score
10
Trophy points
1,298
Activity points
2,697
Hi,

I am trying to understand the behaviour of the LM2577 regulator.

I require to generate 9 VDC (100 mA max current) output. The input voltage will start from 5 VDC and go upto 30 VDC, the output voltage and current must be maintained.

I have calculated the R1 and R2 resistance values. However I am not clear what happens when input voltage is equal or more than 9 VDC, does the regulator step down the voltage automatically ? Assume load current is constant at 100 mA.

Also is there any other chip similar to the LM2577 but in 8 pin DIP form ?

Thanks
a
 

Hi,

as the name says: it is a step up converter.
Input voltage < output voltage.
(With an input voltage of 30V I expect an unregulated (switcher is disabled) output voltage of about 29V. Sounds not good for your application?)

In your case the input voltage can be lower as well as higher than the output voltage.
--> look for buck-boost converters or SEPIC converters.

(Maybe there are design guides to use the LM2577 as SEPIC. Datasheet will tell you)

Klaus
 

All integrated SMPS regulators with a bottom switch, like the LM2577, can be used in a SEPIC configuration.

However, since a SEPIC utilizes a coupled inductor (or two independent inductors) the design equations are different and not covered in the LM2577 datasheet.
There are other devices like the TPS55340 or LM5001 which do.

I would advise you to study its datasheet or of other similar components.
 
thanks all for the quick help
 

The buck-boost (per post #2) is a possibility. It inverts the supply polarity. For 5V input you might run it at 67% duty cycle. For 30V input, 13% duty cycle. You'd get output at -9V 100mA.

As for voltage regulation, the negative output is a peculiar case. The negative V cannot be compared directly to a reference voltage elsewhere in the circuit. However it should be possible to level-shift (or other method) to allow you to regulate the output. I have no experience with the LM2577, so I can't say what it is capable of.
 
  • Like
Reactions: arbj2

    A

    arbj2

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top