This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Hello. I'm building a buck dc/dc power supply with the UC3823a pwm controller. How do I control the Pwm signal? I don't understand how i should calculate the value of my resistors and capacitors. Can anyone help me understanding the pwm controller.
In reply to Morten Paulsen:
The attached should give you some idea about feedback loop. I think you should be discussing these issues with your Prof. That's what he is being paid to do.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
In reply to John Bottrill:
I having some problem switching my mosfet on and off. This result in a warm mosfet. How can i get it work better?
This is the pwm signal, and the voltage on the gate of the mosfet.
Your gate voltage has to be higher than the source to have the FET "ON" and the drive impedance (100 ohms) you are using looks to be to much.
The gate voltage is going from 0 to 30 V for switching the mosfet on and off. The schematic is working, until the mosfet get to hot. I Tried up to 150 VAc in today, and the problem is that the mosfet gets superhot and breaks. There is obliviously too much heat loss in the mosfet. And i dont under stand why. The gate signal was better than the picture from my last post. Would this design work at all? Could it be an idea to put the mosfet between ground and regulate diffident ground planes?
The data sheet says that there should be an 1 mF on Vref. Isn't 1 mF a lot? Why is it so high?
The Terminal Function Table on page 3 says the pin should be bypassed by 0.1uF ceramic LOW ESR LOW ESL cap with minimal trace length.
Figure 14 page 11 shows it as 0.1uF.
I suspect that the 1 - mF on page 10 is the difference in the type font where the "m" of the "mF" is not "symbol" font.
I would expect that a 1 uF cap would be acceptable even with the other two places specifying 0.1 uF
HelloNow when I'm testing, I gets some problems. The the duty cycle gets low very fast. It goes from about 60% to about 5% when the input voltage goes from 22-30V. When the duty cycle get to low, the regulator stops. It seems that the mosfet does not get enough time to switch on and off, when the duty cylce get very low. I'm running the duty cycle at 40KHz, and tried down to 10 kHz, but I'm still having the same problem. Also the source voltage when the mosfet is off, gets a lot of ringing at a ~50 % duty cylce. Why? Do I need to change something in my buck circuit to improve this? See the picture. I'm also attaching the circuit as it is know
Ringing:. BLUE (Source voltage on mosfet.)
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.