The solution for generating 555

Discussion in 'The Projects Forum' started by Skfir, Dec 17, 2012.

  1. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    Hello everybody. This is just a notice in case some newbie like myself has the same problem. Sometime ago I started a discussion, concerned with the fact that when I used NE555 in my flyback DC-DC 5 to 400v convertor everything worked fine, but when I installed any CMOS nothing worked and there was nothing else but noise. So my logic went nuts. Of course I just want to repeat that my schematic was built on a big breadboard with long wires, so potentially everything could cause parasitic generating. Nevertheless I found some temporary solution which helps to stabilize all that. So there is my topology: astable 555 drives ixys IXDD604 driver, which in turn drives a high power mosfer. Mosfet has a coil connected to the drain. When mosfet switches off, the coil charges a capacitor through the fast diode. A comparator or a logic level power MOSFET (better for some reason) is connected to the lower shoulder of the voltage divider, which in turn is connected to the output capacitor. The drain of that MOSFET is connected to the 5th pin of 555, which makes quite reasonable voltage stabilisation by means of PWM modulation. So, in order to eliminate noise, only two things were necessary:

    1. The output of the driver connects to the gate of the MOSFET through 200ohm resistor. At the same time there is a diode in parallel with that resistor, which helps to discharge the gate quickly. This resistor helps to eliminate oscillations when the MOSFET switches on, since its resistance suppresses oscillations.
    2. There is a fast diode with its anode on the 555th output and cathode on the ground. It helps to cancel oscillations when the MOSFET shuts off. There is also a diode with cathode on the 555th output and anode on the 8th pin. Just in case.

    That is it. I write it as a temporary solution for those electronic greeners like myself who encountered the same problem.