Buck converter for small wind turbine project

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, I working on a buck converter to use with a wind turbine to charge a 12 battery bank,
the real problem is I do not understand what is really needed to turn the MosFet on and off . The circuit is working with a resistive load.

1. The mosfet source is connect to the high side of the load. The mosfet is a IRF510.

2. A IR2117 with bootstrap is being used and is referenced to Vs so the bootstrap capacitor voltage can be charged high enough to turn on the mosfet.

3. A 555 timer is used to control the IR2117 @ 10kHz with a Vcc of 12 volts.

4. A permanent magnet alternator is used to supply Vin and can range from 0 to over 200 volts depending on the permanent magnet alternators RPM.

5. A bench power supply is used to supply power to the IC’s. This will be changed later.

The problem is :
When the resistive load is replace with a 12 volt battery the circuit does not work.
I do not understand why the circuit will work for a resistive load and not with a 12 battery as a load. Any suggestion will be greatly appreciated.

This post is a continuation from :
http://forum.allaboutcircuits.com/newreply.php?do=newreply&noquote=1&p=465253

video shows manual operation of PMA and circuit with resistive load:
http://www.youtube.com/watch?v=B3dLzZZ5jKQ
 

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wayneh

Joined Sep 9, 2010
17,134
i could be wrong but I don't think the driver can ever get the gate voltage up above 12v the way you have it configured. It's a bit hard to read the drawing. Can you watch the gate voltage from your driver? Maybe make a little peak detector circuit to see what the peak output is, if you don't have an oscilloscope.
 

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, thank you for the response. I exchanged the IRF510 with a IRF540 and I am unable replicate the results shown in the last video. It is a puzzling situation. It may require a different bootstrap capacitor or some other solution. I am unable to continue until a solution is found. The circuit will function with a lower load but does not work with 50 watt load. The oscilloscope shows the IRF540 starts to turn on then very quickly turns off, then the Vin gains magnitude and the 555 timing signal shuts down.

I am back working with just a resistive load and I am waiting until I can solve the mosfet exchange problem before I try charging a 12 volt battery.

Comments welcome
 

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wayneh

Joined Sep 9, 2010
17,134
I don't think you'll get much help until your schematic is more readable. Maybe break it into panels or do something to help us see it clearly. And any explanation of the design would help. For instance I don't quite follow what the 555 is doing. The triggering needs to be in synch with the pulses from the alternator. These "active rectifiers" or "ideal diodes" don't usually include a 555 timer; they are self-triggered as they need to be.
 

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
testPhoto to compare if I read it.


1. The mosfet source is connect to the high side of the load. The mosfet is a IRF510.

2. A IR2117 with bootstrap is being used and is referenced to Vs so the bootstrap capacitor voltage can be charged high enough to turn on the mosfet.

3. A 555 timer is used to control the IR2117 @ 10kHz with a Vcc of 12 volts.

4. A permanent magnet alternator is used to supply Vin and can range from 0 to over 200 volts depending on the permanent magnet alternators RPM.

5. A bench power supply is used to supply power to the IC’s. This will be changed later.

The problem is :
When the resistive load is replace with a 12 volt battery the circuit does not work.
I do not understand why the circuit will work for a resistive load and not with a 12 battery as a load. Any suggestion will be greatly appreciated.
 

Attachments

twister007

Joined Feb 29, 2012
50
testPhoto to compare if I read it.


1. The mosfet source is connect to the high side of the load. The mosfet is a IRF510.

2. A IR2117 with bootstrap is being used and is referenced to Vs so the bootstrap capacitor voltage can be charged high enough to turn on the mosfet.

3. A 555 timer is used to control the IR2117 @ 10kHz with a Vcc of 12 volts.

4. A permanent magnet alternator is used to supply Vin and can range from 0 to over 200 volts depending on the permanent magnet alternators RPM.

5. A bench power supply is used to supply power to the IC’s. This will be changed later.

The problem is :
When the resistive load is replace with a 12 volt battery the circuit does not work.
I do not understand why the circuit will work for a resistive load and not with a 12 battery as a load. Any suggestion will be greatly appreciated.
Have you measured the voltage on the gate to source with the battery hooked up?
Usually, n channels work better on the low side, I think.
 

wayneh

Joined Sep 9, 2010
17,134
Thanks for the better picture - I get it now. Forget my "active rectifier" comments.

I'm not sure, but shouldn't power ground be connected to logic ground (see figure 23 in the 2117 application note AN-978)? I still think the problem is your gate voltage not rising above battery plus, which is the MOSFET source voltage.
 
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Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, the video shows a resistive load, the circuit is only working with a resistive load. I would like to make the circuit work as a 12 volt battery charger. When I use a 12 volt battery for the load the mosfet does not turn on.

The bootstrap capacitor of the IR2117 is charged to 10 volts. Vs of the mosfet and the IR2117 are connected to plus 12 volts of the battery. The maximum voltage of the bootstrap capacitor can be +/- 20 volts, is that referenced to, ground or to Vs?? I do not know.

When I use a 12 battery as a load, what does the bootstrap capacitor have to be charged to and what do I use as reference? Thank you for any help received.
 

shortbus

Joined Sep 30, 2009
8,464
Your gate drive doesn't work when wired to the battery because Vs never goes to ground to recharge the bootstrap capacitor. The o'scope pulse show this, the gate turns on until Vs and gate voltage equalize, then gate shuts down. If people will take time to really look at the circuit they will tell you same thing as the other thread, it doesn't do anything. Sorry.
 

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Your gate drive doesn't work when wired to the battery because Vs never goes to ground to recharge the bootstrap capacitor. The o'scope pulse show this, the gate turns on until Vs and gate voltage equalize, then gate shuts down. If people will take time to really look at the circuit they will tell you same thing as the other thread, it doesn't do anything. Sorry.
Hi, thank you for following the project. If I use a voltage charge pump to increase the voltage of the bootstrap capacitor to 20 volts or greater would that turn on the MosFet? The IR2117 says the gate drive output can be +/-20 volts, is that referenced to ground or Vs of the MosFet? Comments welcomes
 

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, new test circuit based on information received and suggestions. Basically it is the same circuit as before with a blocking diode added at the plus battery terminal and a voltage pump for the bootstrap capacitor. Vg - Vs > Vthreshold , 20 - 12 = 8volts.
If it works the mosfet’s can be paralleled and the control circuits can be duplicated for increased current output.
 

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Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, I was able to find all the needed parts to make all the required connections to interface the circuit to a 12 volt battery. I am using two bench power supplies, one to power IC’s and the other for Vin.

I had just a LED and 22kohm resistor from the mosfet Vs to ground and the mosfet was turning on and off.

With a capacitor at the output of the circuit no current would flow into the battery. I removed the capacitor and I was able to measure 0.14 amps flowing into the battery.

I had attached a variable resistor to the 555 to be able to test different duty cycle, I adjusted the variable resistor to low and the 555 fried, so I have to purchase some replacements before I can continue testing. I will post more test results after I replace the 555.
 

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shortbus

Joined Sep 30, 2009
8,464
Now you have a pulsing on off switch to your battery, NOT a 'buck' converter. To be a buck or any other type converter, your circuit must measure the input voltage against the output voltage, and make adjustments to the circuit to keep the output at the desired level. Yours doesn't do any of this.
 

Thread Starter

Burnit0017

Joined Feb 15, 2010
101
Hi, thank you for checking the circuit. It was only working for a short time before I fried the 555. The first circuit configuration does work with a resistive load. I am now trying to find a circuit configuration that will function as a 12 volt battery charger.

Is the blocking diode in the right place?

I am still having trouble trying to understand; what is required for the N channel mosfet to turn on and off when a battery is connected for a load?

As I understand it if, Vg - Vs > Vthreshold then the N channel will turn on.

I do not have any experience with this type circuit, thanks again for helping me not to go off in the wrong direction. I am still searching for a solution. Comments welcome.
 
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