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LM2577: current limiter

Hi,

I have a working board with a DC-DC step up with a LM2577-ADJ. Some more info:

- input voltage: 12V

- output voltage: 13V-19V

- output current: up to 2A

The output voltage is selected by a digital potentiometer inserter in the feedback voltage divider.

I want to add a current limiter in order to lower the output voltage if the output current grow over 2A.

What's the best way to achieve this?

I can change the IC with another but I need a TO220 package and the same configuration. In other words, it should be nice a similar DC-DC with the Isense input pin.

May you suggest something?

Thanks! Marco

Reply to
Marco Trapanese
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Marco Trapanese wrote in news:i7nlhn$mr$ snipped-for-privacy@tdi.cu.mi.it:

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Reply to
Hammy

Il 26/09/2010 19:46, Hammy ha scritto:

As I can see, the overcurrent protection is built-in. I can't change it, can I?

Marco

Reply to
Marco Trapanese

Marco Trapanese wrote in news:i7o1tv$b4b$ snipped-for-privacy@tdi.cu.mi.it:

Nope sorry just had a quick look.

You can try Murata to see if they have a small module that can fit your exsisting footprint and specs like these.

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If it is just a few you can make your own like the one above useing one of the numerous boost controllers out there that has built in current limiting.

Another simple hystertic controller

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Reply to
Hammy

How about adding your own current limiting cct. It can tap into the voltage feedback. When current limit is reached it increaces the voltage at the fedback pin to the lm2577(maybe via a diode) The 2577 then "thinks" the output voltage is to high and it reduces accordingly. Might not be the best solution in the world , but is an easy after fit , and it does work. Rob

Reply to
neddie

neddie wrote in news: snipped-for-privacy@t20g2000yqa.googlegroups.co m:

Good idea.

Reply to
Hammy

There's high-side current monitor chips that can do that almost directly (tie into the FB node as Neddie suggested). Some can have the sense resistor float dozens of volts above ground. I have done stuff like that many times, where 3-4 things tied into the FB node. Voltage, current, temperature, dance contest results, and whatnot.

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Regards, Joerg

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Reply to
Joerg

Il 28/09/2010 13:26, neddie ha scritto:

Yes, I will do that if I don't find a suitable device. The problem is the space... I don't have much on the board.

Marco

Reply to
Marco Trapanese

ZXCT1009 come to mind. Small sot 23 package.

Reply to
neddie

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