Hello,
I'm having an issue with the power from a 7805 5V linear regulator. The issue is that the voltage varies when I switch off a high current, high side, MOSFET. It appears that this causes a voltage fluctuation on my 12V battery and this then upsets the 5V regulated supply for the logic side of my circuit an my PIC resets.
I looked at the datasheet for the 7805 and they reccomend a 0.33uF filter cap on the input and a 0.1uF on the output. I have a 100uF and 10uF respectively (only because I found that on a micro tutorial years ago). So I guess my question may really be based on how these filter caps operate. Wouldn't a larger cap, like I have, simply store more power and respond just as quickly as a smaller cap? Suggestions on how to isolate the 5V side of my circuit?
The top plot is Channel 2, the 5V "regulated" power, at 1V/division. You can see that it's dipping below 4V. As the current switched by the MOSFET increases this gets more dramatic until the PIC resets. The bottom plot is the MOSFET gate at 10V/division.
The schematic for how the LM7805AC is connected is here:
http://2.bp.blogspot.com/-fcShHZt2i...TRF5g/s1600/2-12-11+Solar+Board+Schematic.png
The schematic for the MOSFET switching is here:
http://2.bp.blogspot.com/-IfCgle3nE...0/HIGH_SIDE_PANEL_DRIVER+entire+schematic.png
I'm having an issue with the power from a 7805 5V linear regulator. The issue is that the voltage varies when I switch off a high current, high side, MOSFET. It appears that this causes a voltage fluctuation on my 12V battery and this then upsets the 5V regulated supply for the logic side of my circuit an my PIC resets.
I looked at the datasheet for the 7805 and they reccomend a 0.33uF filter cap on the input and a 0.1uF on the output. I have a 100uF and 10uF respectively (only because I found that on a micro tutorial years ago). So I guess my question may really be based on how these filter caps operate. Wouldn't a larger cap, like I have, simply store more power and respond just as quickly as a smaller cap? Suggestions on how to isolate the 5V side of my circuit?
The top plot is Channel 2, the 5V "regulated" power, at 1V/division. You can see that it's dipping below 4V. As the current switched by the MOSFET increases this gets more dramatic until the PIC resets. The bottom plot is the MOSFET gate at 10V/division.
The schematic for how the LM7805AC is connected is here:
http://2.bp.blogspot.com/-fcShHZt2i...TRF5g/s1600/2-12-11+Solar+Board+Schematic.png
The schematic for the MOSFET switching is here:
http://2.bp.blogspot.com/-IfCgle3nE...0/HIGH_SIDE_PANEL_DRIVER+entire+schematic.png
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