Power supply problem / PWM
Power supply problem / PWM
(OP)
Hi All,
I have a problem using (what I considered) a simple circuit.
I use a microcontroller that generates a PWM signal that feeds a gate of a N-channel Logic level MOSFET. When I switch the LOAD on and off (without PWM) the 5V (that powers the micro) is perfectly stable. When I use PWM to switch the load the power changes as you can see in the attached picture. The micro of course goes crazy from time to time.
-The load is a LED board powered at 12V 25 groups of 5 leds with current limiting resistors.
- The 12 V are provided by a bench power supply.
- The 5V are regulated on board using a 7805.
- No gate resistors
- I have all decoupling caps in VCC /GND
- Changing PWM frequency as no effect.
Can some one help please?
Thanks in advance.
I have a problem using (what I considered) a simple circuit.
I use a microcontroller that generates a PWM signal that feeds a gate of a N-channel Logic level MOSFET. When I switch the LOAD on and off (without PWM) the 5V (that powers the micro) is perfectly stable. When I use PWM to switch the load the power changes as you can see in the attached picture. The micro of course goes crazy from time to time.
-The load is a LED board powered at 12V 25 groups of 5 leds with current limiting resistors.
- The 12 V are provided by a bench power supply.
- The 5V are regulated on board using a 7805.
- No gate resistors
- I have all decoupling caps in VCC /GND
- Changing PWM frequency as no effect.
Can some one help please?
Thanks in advance.





RE: Power supply problem / PWM
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Power supply problem / PWM
let us have a look at the schematic
regards
rodrigo
RE: Power supply problem / PWM
I have had both problems occasionally.
Put a large >1000uF cap right next to your board in parallel to to your supply lead and lets see what transpires.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power supply problem / PWM
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power supply problem / PWM
The large capacitor at the end of the power supply leads (at the input terminal of the 7805) solve the problem. Also I have increased the value of the capacitor at the ouput. Now I have a clean VCC at any duty cycle.
Learning every time...
Thanks for your help guys!
RE: Power supply problem / PWM
I killed a couple of 78xx's this way.
Good luck!
RE: Power supply problem / PWM
TTFN
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