photo-voltaic dc-dc boost converter

hi everyone, pls i am designing pv boost converter, i have finished designing the circuit. i simulated it with proteus but the waveform is giving me is somehow. the output is 24v when i used oscilloscope cursor to measure it but it is not giving me perfect pwm that I want. the output is only rising above the 12v input, not returning. please could anyone understand me and help me to solve this problem. thanks

PLease notice that forum rules prohibit multi-postings.

You can hardly expect an answer without posting a meaningful circuit diagram.

seunatoki said:

the output is only rising above the 12v input, not returning.

Click to expand...

It is a boost converter. Thus the output is supposed to be above the input. What is the problem?

please post your circuit, that will help to find the error.

Dear sir,
Please see attached
Thanks,
Atoki

That's plain wierd!

You have a current limited input rated at 3A max which wastes a lot of current in R5, a voltage booster using a microprocessor that needs an additional supply from somewhere, a 1 Amp / 4V regulator to power an op-amp that consumes 40uA and a 24V shunt regulator which will fry itself if it gets the chance. Add to that some rather odd capacitor values, I'm not suprised it doesn't perform well.

Brian.

mr brian, please what could i do now to adjust it ? i have run out of idea that is why i came here to share my problem.

please and please share with me the idea, it is like you fathom the problem better.

thanks

Well I'm not going to redesign it for you but I will give you some clues:

1. completely remove Q1/R5 and everything before it. Feed the 14V directly across C1.
2. completely remove Q3/D4 as they do nothing, if they ever did start to conduct they would burn up immediately.
3. increase C1 to maybe 1,000uF
4. remove U2/R6/R7 and replace them with a 7805 (or 78L05) fixed regulator instead. This will let you power the PIC with 5V as well.
5. remove C4, I'm not sure what it is supposed to do.
6. increase R13 to say 470 Ohms and add a capacitor across it, 100uF or more.
7. there is no feedback path to regulate the output voltage, add a potential divider across the output and feed the center back to a PIC ADC input.
8. drop the values of R8/R9 by a factor of 10 times at least. They are only there to monitor the battery voltage, with such high values all you do is make it more prone to noise pick up.

Even then, you must remember that this is a boost circuit, even if you turn the PWM off completely, the output will not go lower than the battery voltage less the drop across D3.

Brian.

the first circuit you said that i should remove, i designed that as solar panel that can give me 12V. all I want to is 12v input and 24v at the output with maximum output current of 0.3Amps. for my inductor value, i calculated it to be 500uH, frequency 50kHZ. i used voltage divider for voltage sensing and U3 and R10 for current sensing.

any further clue ?
thanks

The first stage is actually a constant current generator set to about 1.2A. Assuming you need at least 6V to allow the LM317 to work, it would require a battery voltage of at least 30V (6 + (20 * 1.2)) before it operated properly and R5 would have to be rated at 30W. If you intend it to be a 12V voltage regulator, at the currents you are using, a 7812 would be a better choice.

I'm not sure what you mean by "voltage divider for voltage sensing", if it's R8 & R9, then you are sensing the input voltage, to be able to regulate the voltage at the output they should be across R13.

Brian.