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Electronics => Beginners => Topic started by: Magnets on March 11, 2016, 08:21:40 pm

Title: Using a MOSFET to control a Buck module
Post by: Magnets on March 11, 2016, 08:21:40 pm
I have one of these XL4005 buck modules to run an LED and want to control the module via a mosfet (RFP30N06LE).

http://www.aliexpress.com/item/High-Quality-5A-DC-to-DC-CC-CV-Lithium-Battery-Step-down-Charging-Board-Led-Power/32388356240.html (http://www.aliexpress.com/item/High-Quality-5A-DC-to-DC-CC-CV-Lithium-Battery-Step-down-Charging-Board-Led-Power/32388356240.html)

Do I need a diode across the buck to protect the mosfet or can I just run it like this with the buck in place of the bulb (3rd diagram)

http://bildr.org/2012/03/rfp30n06le-arduino/ (http://bildr.org/2012/03/rfp30n06le-arduino/)

Thanks
Title: Re: Using a MOSFET to control a Buck module
Post by: Simon on March 11, 2016, 08:23:30 pm
you should not have problems and not need a diode if the buck converter is made properly
Title: Re: Using a MOSFET to control a Buck module
Post by: Magnets on March 12, 2016, 07:42:12 pm
Quote from: Simon on March 11, 2016, 08:23:30 pm
you should not have problems and not need a diode if the buck converter is made properly

Is there anything critical or obvious that I could observe to determine if that's the case?

Thanks
Title: Re: Using a MOSFET to control a Buck module
Post by: Seekonk on March 12, 2016, 08:56:25 pm
I question the need for it at all.  You could send a digital 5V signal through a diode and fake the feedback loop into thinking the output voltage is too high.  That would shut down any type  converter.  If it is anything like the 2596, pin #5  is the shutdown pin.  Raising it above ground will shut down the converter.  This pin is fast and you could PWM the converter for variable intensity.
Title: Re: Using a MOSFET to control a Buck module
Post by: Magnets on March 12, 2016, 11:27:44 pm
Quote from: Seekonk on March 12, 2016, 08:56:25 pm
I question the need for it at all.  You could send a digital 5V signal through a diode and fake the feedback loop into thinking the output voltage is too high.  That would shut down any type  converter.  If it is anything like the 2596, pin #5  is the shutdown pin.  Raising it above ground will shut down the converter.  This pin is fast and you could PWM the converter for variable intensity.

Great point, the module actually has pads for pin 4 (EN) and ground pulled out which I never realised. It still uses 5.6ma when disabled, which I assume is the onboard LED.