hazzard043
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Hi, 2 months ago I started designing my own SMPS based on Texas Instruments UCC3808 Current-mode PWM controller. It's one of the rare PWM controllers (current-mode ones) that have overcurrent protection.
Schematics is in attachment.
My problem is, everything is working, i have 23.9V @ 0A, and voltage stay at that value until i reach 1.5A, then voltage start dropping. Power supply is working at costant power mode. Short circuit current is 280 mA.
As you can see, I added slope compensation becouse duty cycle is above 50% (2×25%).
I wanted to increase current limit, but i cant get out more than 2A, and i tried to modify shunt, then i tried voltage divider to lower the current sense signal (I was carefull not to scramble RC constant on pin 3). Nothing, i just make power supply unstable and noisy.
I tried to modify 20k resistor going from VCC to 2N2905 emiter. Nothing. I tried add aditional shunt resistor. Nothing. I shorted pin 3 to ground, 23.9V even at 5A and no noise at all, MOSFETs are at 28°C
I have no idea what is wrong.
Schematics is in attachment.
My problem is, everything is working, i have 23.9V @ 0A, and voltage stay at that value until i reach 1.5A, then voltage start dropping. Power supply is working at costant power mode. Short circuit current is 280 mA.
As you can see, I added slope compensation becouse duty cycle is above 50% (2×25%).
I wanted to increase current limit, but i cant get out more than 2A, and i tried to modify shunt, then i tried voltage divider to lower the current sense signal (I was carefull not to scramble RC constant on pin 3). Nothing, i just make power supply unstable and noisy.
I tried to modify 20k resistor going from VCC to 2N2905 emiter. Nothing. I tried add aditional shunt resistor. Nothing. I shorted pin 3 to ground, 23.9V even at 5A and no noise at all, MOSFETs are at 28°C
I have no idea what is wrong.
