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Electronics => Beginners => Topic started by: little_carlos on April 03, 2016, 05:22:46 am

Title: how is current limited or regulated on step down buck converters?
Post by: little_carlos on April 03, 2016, 05:22:46 am

Hi, how can the current can be limited or regulated on a step down buck converter? if the voltage is driven by the duty cycle, is the current determined by frecuency or something? how can i regulate the current on a simple switcher like lm2576 or similar?

Title: Re: how is current limited or regulated on step down buck converters?
Post by: Seekonk on April 03, 2016, 06:38:48 am

You fake the feedback pin into thinking the output is higher than it actually is.   Use a diode to isolate  the feedback pin from current control circuit.   Low it is ignored and going high will shut down the PWM. If I remember this is similar to 2596 and pin #5 can also do this.  Let it go high ans it shuts down.  This pin is very fast and it will look like analog control.

Title: Re: how is current limited or regulated on step down buck converters?
Post by: mikerj on April 03, 2016, 10:15:36 am

Quote from: little_carlos on April 03, 2016, 05:22:46 am

if the voltage is driven by the duty cycle, is the current determined by frecuency or something?

Ohms law: I=V/R

For a normal resistive load, current is determined by the voltage. To reduce the current you reduce the voltage, exactly like any other kind of power supply.  As Seekonk says, to reduce the output voltage you raise the voltage on the feedback pin.