Buck converter for small wind turbine project

[Burnit0017]

Hi, the IR2117 have arrived and I completed all the high current connections of the buck converter. Using a Zener diode as Vcc to power just the nand gate oscillator I was able to illuminate a LED with a quarter turn of the PMA. Not great results but it is a start.  I have to test the IR2117 with the oscilloscope to determine if HO is oscillating. I wired the test circuit and used a 12 volt halogen light as a test load and spun the PMA manually. The PMA was very easy to spin until the MOSFET turn on, then I was unable to spin the PMA. I believe the MOSFET is not turning off. My concerns are there is a lot energy stored in the input capacitor and I do not want to harm my oscilloscope. Are there any points I should avoid when testing the circuit?? The chassis ground and each channel ground are a the same common point, is there a safe method to use when testing the circuit with the scope? Comments welcome.     

[Burnit0017]

Not a valid youtube URL

Hi, I changed the load to a watt 12 volt light. The video shows the LED on the right then the load lights up. The PMA is very hard to spin.

[boB]

Burnit, could you please make a bit higher resolution schematic so I can read the values and net names ?


Thanks,
boB

[Burnit0017]

http://web.mit.edu/6.131/www/datasheets/float_drive.pdf     (pg. 16 and 17 show circuit)

Hi, I tried to increase the size of requested items. I use the key board control key and spin the center mouse wheel to magnify the image. I finally had time to test the circuit with a oscilloscope and found the oscillator is working but the gate driver is not firing and the MOSFET is passing current that is shown in the video with out being turned on. Today I am going try to get the gate drive to fire and replace the MOSFET. I did find the application sheet for the IR2117. I will report results when available. Thank you for the help I am receiving.

[boB]

Ahhhh...  Much better !

Those IR21xx parts are very nice.   My only problem with them is that they don't have a very high Vcc rating.  i.e.  usually around 20 volts or less.

Just have to be careful not to exceed their maximum ratings.

boB

PS, nice app note.  I don't think I'd seen that particular one from IR before.

[Burnit0017]

Hi, I found one problem. The nand oscillator is only putting out a 5 volt timing signal. The IR2117 has a input low voltage lockout. I have to increase the voltage of the timing signal.
I guess not all 4000 series are the same, thing do change.  The new used scope works well, it is fast, gives to much information and has to many buttons but I am happy to have it.

From the application notes it looks like the IR2125 is designed for a 12 volt battery charging circuit. The IR2117 is designed for resistive loads. I am proceeding with what I have. I will be happy if I can just get a MOSFET to trigger at this time and I will post results when available.   

[rossw]

Hi, I found one problem. The nand oscillator is only putting out a 5 volt timing signal. The IR2117 has a input low voltage lockout. I have to increase the voltage of the timing signal.

From the application notes it looks like the IR2125 is designed for a 12 volt battery charging circuit. The IR2117 is designed for resistive loads.

I haven't looked at the application notes for your driver - but it would seem "likely" to me that it has a degree of input waveform shaping, and doesn't require the super-fast rise and fall times you need for the fet itself.

Therefore, it MIGHT be simple and easy to either use a diode/resistor pair to generate a 0.9-12V approx waveform from the IC output to the driver chip, or a single-transistor as a open-collector buffer to give you a nearly 0-12V drive for your IR21xx chip. The relatively slow rise-time shouldn't be a problem to the fet, as the driver should square it up?

[Burnit0017]

Hi, photo shows input timing signal from 555 timer and output (HO) of  IR2117. The MOSFET is not connected.  I had to connect Vs to ground. Duty cycle is a little greater then 50%.

The application notes says that the logic ground and power ground should not be connected but their diagram shows they are connected, I find this very confusing. I am not sure where to generate Vcc? Comments welcome.

[Burnit0017]

Hi, I may have found a solution to provide an isolated Vcc. I may not sure if it work, comments welcome. I will post results when available.

[ghurd]

Might try a 7555?
G-

[Burnit0017]

Hi,  The photo displays the Vs wave form on top and the IR2117 trigger input on the bottom. I am using switching diodes because I do not have any fast recovery diodes.

The only way I could get the MosFet to turn off is to connect  Vs from the IR2117 to ground. Control signal is 10 kHz and I am using bench power supplies and a 12 volt light for a load.

I am making progress. 

[Cornelius]

I'm no expert at switching, but i've made one once, and i didn't get the signals stable before i added a ferrite bead after the gate resistor, close to the Gate of the fet, and a diode from the gate to the ground to protect the gate from reverse currents.

To get the fet to turn off properly, put a 100k resistor from the gate to ground.

[oztules]

What does Vgs look like, and Vds. Is the bottom trace Vgs or is it the input to the driver.... what does the output at the driver look like compared to the Vgs trace.

It looks hot and scary that top trace.



..................oztules

[ghurd]

It looks hot and scary that top trace.

I don't think I ever saw anything quite like that before.
G-

[Wolvenar]

It looks hot and scary that top trace.

I don't think I ever saw anything quite like that before.
G-

I was thinking the same.. wow.

I am making progress. 

I'll have to take your word on that.. What were you expecting there?