Unstable DC-DC buck converter Output

[Manmash]

Hi everyone,

Attached is my first attempt to build a buck converter that will give a 3v output. I'm using the TL494 to switch the FET .

the oscillator frequency is set to 100khz using 0.01uF cap and 1kohm res. according to the TL494 application note, the duty cycle can be controlled by controlling the voltage input of the dead-time control input (pin4) as the input voltage is varied from 0 to 3.3. I tried that, but the ouput i keep getting is unstable. it keeps increasing from 0 to 7v then decreasing to zero and so on. what am i exactly missing?
any help is highly appreciated!!!
Regards

 

[andre_luis]

try some ceramic capacitor at PIN 1

 

[Manmash]

I will try that, but can you tell me what effect that exactly makes?
many thanks

 

[andre_luis]

Capacitors acts like Integrators ( 'I' of 'PID' control ), and turn the behaviour of feedbackad signal more stable, due it slew rate become more slow.

 

[Manmash]

should the cap be connected to the feedback pin then, that is pin 3 ?