# Halfbridge with an inductive load of 24 µH

Discussion in 'The Projects Forum' started by Alex009, Apr 30, 2015.

1. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
Good morning everyone,

I could Need a Little help with the attached circuit.

So the basic idea is that the halfbridge driver drives the 2 nmos-gates. So there should be always 1 active (well atleast if you dont consider the fact that there is a deadtime). This should be done at a frequenzy of 125 kHz (T ~ 8 µs). So I got a variable R2 of 5.5 k Ohm (potentiometer) and the capacitor C3 to make sure the halfbridge driver works at this frequenzy.

--> I thought my 24 V DC would Change to a 0V to 24 V square wave (right before C2) and then Change to an -12V - 12 V AC (right before L1). But unfortunately when getting the whole thing done on a testing board nothing happend. I simple did not get a switching Signal out of the halfbridge driver ( --> neither did i get a square wave at one of the mosfets).

So do you have any ideas or suggestions to help me with that issue? I will add the mosfet as soon as I m able to find out which ones I used (I'm currently not in reach of these).
Maybe changing some values of c's and r's?

I m using the following halfbridge driver: IRS2153 http://www.irf.com/product-info/datasheets/data/irs2153d.pdf

Best regards
Alex

• ###### CircuitHelp.PNG
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Last edited: Apr 30, 2015
2. ### ScottWang Moderator

Aug 23, 2012
4,930
777
When M1 is turn on then Vds=0V, Vd=Vs=24V.
The condition to keep M1 turn on that it is Vgs = 5V or 10V, so the Vg to ground will be Vg = 24V+5V=29V or Vg=24V+10V=34V.

3. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
1,135
There could be various reasons why your breadboard circuit didn't work, but the LTspice simulation won't work properly unless you choose a value for the NMOS FETs.

4. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
@ScottWang well thats exactly my Problem. gate-source voltage is always ~0 V for both Mosfets
@Alec_t Yes it doesnt. There is also no LTSpice model for the halfbridge driver - I did this in LTSpice for you to understand the circuit i m using (The IRS2153 is ONLY REPRESENTED by a standard 8 pin package) - since i didnt get a real one on the Internet. It would be helpful if you could give me a hint concerning on of these various reasons.

5. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
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Incorrect/missing connections, high resistance connections, faulty/fried component, wrong component value, stray capacitance, stray wiring inductance, .....

Last edited: May 1, 2015
6. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
Well since i double checked Connections and was measuring several points i dont see this to be the case. Also I was double checking the components i used. They all fit the schematic. So thats why I asked if there is anything wrong with it.

7. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
1,135
You say you are using a IRS2154, but the link is for a IRS2153 ?? Is the pin-out and function the same?
What waveforms/voltages do you get at pins 3, 5 and 7?

8. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
Oh ty for telling me. The link is actually the correct one. Just a typo. I will edit this asap.

I got on both 5 and 7 a ~200 mV Voltage which looks like noise to me.

9. ### ScottWang Moderator

Aug 23, 2012
4,930
777
If you have O'scope then show the waveforms and the photos of breadboard at different angles.

10. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
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Then it looks like there is a wiring error, a supply voltage/ground missing, or a dead/fake IC. You could try re-positioning wiring on the breadboard, in case there is a dodgy socket.
What was the pin 3 waveform like?​

11. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
Hey I will Report back on monday and upload the Pictures of the waveforms since I m not having acces to a scope right now. Everything is closed here til monday
I will also try to use another IC since i ordered a few of them.
Have a nice Weekend and ty so far.

12. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
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From the IC datasheet, the recommended max supply current Icc is 5mA and the minimum Vcc clamp voltage is 14.4V. With R3=470Ω and V1=24V your Icc could be (24-14.4)/470 = 20.4 mA ! That is only just over the absolute maximum allowable, but may well have fried the IC . I draw your attention to Note 1 at the foot of page 2 of the datasheet. Perhaps make R3=2k2 to 4k7?

Last edited: May 1, 2015
13. ### Alec_t AAC Fanatic!

Sep 17, 2013
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I couldn't find a model of the IRS2153 anywhere on the web, so I built one. I've attached it below, in case it helps. It has a few limitations (described in the attached .sub file, readable with a text editor).

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14. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
@Alec_t Thank you very much for your help. As promised i will provide you with the waveforms of all out-/Input Pins of the IC.
For doing that I also simplified the circuit as shown in the Picture below.

Pin 1:

Pin 2:

Pin 3:

Pin 5:

Pin 7:

Pin 8:

All waves except for the one on pin 7 are looking good to me. I also tried to Change the capacitor c5 to a slightly higher value (used 1µF instead) but this didn't change anything. I figured this was also the Problem my circuit suffered when using the mosfets.
The frequency is also alright. I initially wanted a frequenzy of ~125kHz so I will just change the valuce of c3. I also do not think that this is the Major Problem with this. Since when changing the capacitor to a much higher value (operating frequency ~5kHz) the pin 7 "Problem" still occured.

Would be nice to hear from you again.

BR
Alex

Edit: Also thank you for the hint concerning R3. Will probably chose 1k Ohm.

Last edited: May 7, 2015
15. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
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It's not surprising pin 7 doesn't do the same sort of switching as pin 5. Pin 6 should not be grounded. The bootstrap can't work unless the lower end of C5 can be pulled high and low.
With pins 5 and 7 each grounded via 33 Ohms they will have an excessive load, since they are rated to source only ~180mA.

Last edited: May 7, 2015
16. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
@Alec_t So what would you suggest for connecting Pin 6 to for testing? But obviously the IC works perfectly fine . My next guess was changing my Cboot to a higher value ~5µ. What is your thought on that?
BR Alex

Edit: Could the capacitive / inductive load cause such Problems?
Could the high frequency cause Problems?

I' m using the following Mosfet: STP36NF06 - http://www.farnell.com/datasheets/1718576.pdf -. What are your thoughts on this one?

Last edited: May 8, 2015
17. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,973
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Connect it as in post #1.
I'd leave it at 100n, unless you find the boot voltage at pin 8 drooping.
So what problem are you referring to?
That FET looks fine.

18. ### Alex009 Thread Starter Member

Jul 2, 2014
30
0
@Alec_t Yes. I think I found the Problem and going to solve it hopefully 'til tuesday. I accidently bought the wrong capacitor for CT and didn't realize somehow.. It should have had ~1nF instead I bought 0.1 nF and used it on my breadboarded circuit. I'm still wondering why I even got some o.k looking signals :'D Lets hope the whole thing will work with the new capacitor on tuesday.
Oh Boy.. Thank you anyways. I will keep you informed.

BR Alex