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king
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« on: July 02, 2011, 08:44:32 20:44 »

Hi!
I have design the circuit for 24v UPS and i have also got 240Vac at output but problem is that my Mosfets heat up too much, i have tried so  many ways to find the problem but unsuccessful, I have attached the source code as well as schematic please give your valuable comments to solve this problem.

Posted on: July 02, 2011, 08:43:26 pm - Automerged

here is the schematic
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oldvan
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« Reply #1 on: July 02, 2011, 09:27:04 21:27 »

How serious a heat sink do you have on the FETs?

How much power are you running through the circuit?
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pickit2
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« Reply #2 on: July 02, 2011, 09:39:51 21:39 »

The device IR2109 is not the right device for push-pull, it is single drive only with /SD as on/off (unless you have found a new way to use it) Smiley

As to rest of desisn the resistors for driving the power fets are on the low side (I would use 100k for R3, R5 & R7,R8, plus are the 1n4148 and R4 & R6 and D2,D4 needed ? looks like over kill
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elecgreg
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« Reply #3 on: July 03, 2011, 01:52:21 01:52 »

Hello,

are the mosfets heating up as a result of loading on the output or with no load also? Do you have a scope, can you post here or describe the gate drive signals? Look at the shape of them and timing relative to each other.
When you inverter is unloaded what is the current consumption on the 24v supply (rms meter)?

Can you describe the transformer you're using, ratings. In an APC UPS that uses a 24v rail the transformer, when 230vac is applied to the output there is ~16vac on the secondary.

elecgreg
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solutions
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« Reply #4 on: July 03, 2011, 02:49:10 02:49 »

Agree with pickit2.  Ditch the zeners and put a zero ohm resistor in place of the seriess gate diodes. 

Simultaneous two channel scope shots on gates of the two transistors, and then the drains, to eyeball symmetry, r/f times, and possible shoot-through.

If it were me, I'd ditch the optos as well - your transformer already provides isolation. A slow r/f on those could keep the switches in the linear region...another place to have a look with the scope.
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fernandodiaz
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« Reply #5 on: July 03, 2011, 03:27:33 03:27 »

YOU NEED PUT DIODE IN THE MOSFET IN PINS DRAIN AND SOURCE CATODE IN DRAIN  ANODE IN SOURCE TOO  2 RESISTOR 0.1 OHMS 10W IN SERIAL DRAIN AND PIN TRANSFORMER , THE MOSFET WORK BEST WITH RESISTIVE LOADS AND TRASIENT PROTECTION , USE THERMAL DISSIPATION METALS  TOO FAN AS POSSIBLE



http://zone.ni.com/reference/en-XX/help/375472A-01/switch/inductive_load/
http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode
http://services.eng.uts.edu.au/~venkat/pe_html/ch07s2/ch07s2p1.htm
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king
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« Reply #6 on: July 03, 2011, 06:59:39 06:59 »

Hello,

are the mosfets heating up as a result of loading on the output or with no load also? Do you have a scope, can you post here or describe the gate drive signals? Look at the shape of them and timing relative to each other.
When you inverter is unloaded what is the current consumption on the 24v supply (rms meter)?

Can you describe the transformer you're using, ratings. In an APC UPS that uses a 24v rail the transformer, when 230vac is applied to the output there is ~16vac on the secondary.

elecgreg

I have used only one mosfet in each side and my mosfets heat up on No Load and i am using 24V dc power supply in series with 100 watt bulb so if my supply takes current then bulb glows in series but every thing is cool only mosfets in the circuit heats up.
Do i have to use another Driver IC ? please advice
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« Reply #7 on: July 03, 2011, 09:17:00 09:17 »

100W light bulb means 0.5 amp secondary.  That also means 5 amps primary.  I can't read the part number on your switches, but at 0.1ohm RDSon, you're at 2.5W of toasty...yeah, they'll get hot and not much else will apart from the transformer's joule and core heating.

To put the power level in perspective: http://www.jaycar.com.au/productView.asp?ID=TS1537
« Last Edit: July 03, 2011, 09:21:29 09:21 by solutions » Logged
king
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« Reply #8 on: July 03, 2011, 10:46:05 10:46 »

Is this necessary to use dead time between two inverted PWM's to drive transformer in UPS application ?
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elecgreg
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« Reply #9 on: July 03, 2011, 11:11:46 11:11 »

Some dead time or monitoring of the drain of the device switching off is usually used to avoid cross conduction. Many hardware based inverters use controllers that have a dead time forced by there maximum on time, so additional dead time is not always added. A scope will be really useful in the diagnosis of this. Your 100w light bulb (I'm assuming a 24v 100w) in series with the supply could well be saving you from smoking your FETs if there is cross conduction. It's best to be on the safe side when it comes to cross conduction, if your close small changes in temp, supply parameters can be fatal. You need to look at the relative timing of the on and off of each switch, while each device is in partial conduction (gate voltage rising / falling) your cross conduction my not be fatal to the device, but cause heating, get it rally wrong and they will fail. It's not a useful thing to have happening.
You can also see it in the supply current, look for spikes when there is a transition from one FET to the other.
cross conduction is not only a result of incorrect dead time, but get this sorted first, if you have no scope, add 10% and see if your problem goes away.

elecgreg
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« Reply #10 on: July 03, 2011, 03:35:08 15:35 »

I think the IRF driver has internal deadband already, need to check the DS.

Just from your schematic, the mosfet driver is HIGH + LOW side drive while the mosfets is arranged both to be driven LOW - you need DUAL LOW side driver.

What is the frequency?

-ichan
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king
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« Reply #11 on: July 03, 2011, 06:46:38 18:46 »

Thanks for sharing your valuable comments but one thing i have not mentioned here in the post that i am not using Step UP Transformer (24Vac to 220Vac), I am using just for testing Step Down Transformer [220Vac to 12 + 12( 24Vac Center Tape)] and also the resistance of 24vac side is 2.4 Ohms while 220Vac side has 35 Ohms so according to Ohms's law

=>I=V / R = 24 / 1.2 = 20A , could this be the possible cause of Mosfet's Heating.
Kindly advice that my assumption is true or not.
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« Reply #12 on: July 03, 2011, 07:19:30 19:19 »

Sorry but if the power is 24v, the transformer should be 24 +24->220. Considering losses and a possible adjustment to the secondary I I'll take a transformer 20 +20 -> 220. The transformers are bidirectional. A 50-60 Hz can be used either as step-down or step-ups.
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« Reply #13 on: July 03, 2011, 09:05:43 21:05 »

Thanks for sharing your valuable comments but one thing i have not mentioned here in the post that i am not using Step UP Transformer (24Vac to 220Vac), I am using just for testing Step Down Transformer [220Vac to 12 + 12( 24Vac Center Tape)] and also the resistance of 24vac side is 2.4 Ohms while 220Vac side has 35 Ohms so according to Ohms's law

=>I=V / R = 24 / 1.2 = 20A , could this be the possible cause of Mosfet's Heating.
Kindly advice that my assumption is true or not.

You need to factor in that the dc value you're putting on the primary is the peak of the waveform, to get 220ac you need to apply 24ac rms.

For current calculations, think of the dynamic system also, the inductance of the primary at 50hz? You have calculated worst case above.
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« Reply #14 on: July 04, 2011, 08:04:50 08:04 »

OK.  The plot thickens.

You have put 24V on half the transformer. FWIW, one man's step up is a contrarian's step down. Same difference and only depends how you hook it up.

You are firing one FET, while the other is off with that half bridge driver, into the fewer winding side of the Xformer. There is no DC if you do it right, nor is there a "24AC rms".  Simplistically, that means for a 24VCT, you are applying 24V square wave to a winding ratio of 12:220, not 24:220.  This means your output voltage is likely 440VAC peak (NOT rms).  Increasing the output voltage means 2X the power you have assumed into that 100W bulb (and as a consequence in those switches)....you are likely going to kill yourself if you try to measure that accidental voltage, BTW.

I am assuming you are outputting a sine wave PWM pulse sequence into those switches, given your use of a 60Hz transformer?  You seem to be avoiding mention of what the drive looks like, but there would be no reason for that PIC otherwise.  You'll need to ensure you factor the 440V peak into your tables, instead of the 311V, or power output into an assumed load will be much higher (double...isn't math wonderful?), as will the voltage (by 41%).

It's probably easier to hack one of these, by the way: http://www.walmart.com/ip/Bravo-View-150-Watt-Lighter-Inverter/9729856?findingMethod=rr
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king
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« Reply #15 on: July 04, 2011, 07:18:19 19:18 »

I think some misconceptions has been created here,
if you consider 12V UPS then it has a transformer of 6+6 to 220Vac not 12+12 to 220Vac and at center we will connect 12V battery positive terminal and operate transformer in push pull topology so by using push pull topology the voltage at primary will reach upto 18Vac and similarly when ups gone on charging then by 220Vac we will get 12Vac or 18Vdc to charge 12V battery.

and i have also measure the voltage at the output it is 225Vac and where i have apply PWM it has 38vac (Operated in push pull)
« Last Edit: July 04, 2011, 07:25:35 19:25 by king » Logged
elecgreg
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« Reply #16 on: July 04, 2011, 09:34:21 21:34 »

I think some misconceptions has been created here,
if you consider 12V UPS then it has a transformer of 6+6 to 220Vac not 12+12 to 220Vac and at center we will connect 12V battery positive terminal and operate transformer in push pull topology so by using push pull topology the voltage at primary will reach upto 18Vac and similarly when ups gone on charging then by 220Vac we will get 12Vac or 18Vdc to charge 12V battery.

and i have also measure the voltage at the output it is 225Vac and where i have apply PWM it has 38vac (Operated in push pull)

Are you making a square wave, modified sine or a pwm generated sine? This will infulence your turns ratio. Also what are you taking your measurements with?

Your 100w bulb, is it a load on the mains side or current limiter on the 24v side?

elecgreg
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pickit2
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« Reply #17 on: July 04, 2011, 11:37:23 23:37 »

Quote from: King
we will connect 12V battery positive terminal and operate transformer in push pull topology

So where are we going wrong?
Quote from: pickit2
The device IR2109 is not the right device for push-pull
and this
Just from your schematic, the mosfet driver is HIGH + LOW side drive while the mosfets is arranged both to be driven LOW - you need DUAL LOW side driver.
-ichan
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king
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« Reply #18 on: July 06, 2011, 07:00:09 19:00 »

So where are we going wrong?and this
I am generating PWM sine wave and 100w bulb is connected in series to just ensure that no high current has been flowing from the circuit and also prevent circuit from short circuit it is just a safety not a load

Posted on: July 06, 2011, 06:50:18 pm - Automerged

Just from your schematic, the mosfet driver is HIGH + LOW side drive while the mosfets is arranged both to be driven LOW - you need DUAL LOW side driver.
-ichan

If you see the schematic then i have ground the VS terminal and in this configuration high side will work same as low side
because

VB=15V (High side voltage)
VS = Gnd

VCC=15V (Low side voltage)
VSS = Gnd
so there is no difference
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« Reply #19 on: July 07, 2011, 01:14:38 13:14 »

Hi,
There are 2 reasons that make the mosfet heat up.

1.  The on resistance is high.

The main reason to have high on resistance is the gate voltage.  You have to check whether the gate voltage is high enough to maintain a low on resistance.
All this is affected by the driver IC you use and the combination of the gate resistances and diode.
If you have a scope, check level of the pulse you have at the gate.
TGhe specs of your mosfet say that at VGS= 10V; ID= 30A and on resistance is 0.016R.  This is very good provided the gate voltage is 10V. If it is lower then the mosfet is not fully on and the resistance is higher.

2.  The back e.m.f. due to the inductive load (transformer) produces enough head in the internal protection diode of the mosfet.

In such a case use an external fast switching diode mounted on a heat sink for both mosfets
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king
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« Reply #20 on: July 12, 2011, 04:52:02 16:52 »

I have found a new design of 24V UPS, please find the attached file and i want ask one question that can i use in place of Power transformer (in the attached file) a normal transformer of 12-0-12 or i have to use high frequency transformer ?

Posted on: July 12, 2011, 04:45:44 pm - Automerged

Here is the file
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« Reply #21 on: July 13, 2011, 06:30:09 06:30 »

Hi, you have to use a transformer designed to run at the switching frequency (100khZ in this case), if by normal you mean mains (50 or 60Hz) this will not work in this circuit.

elecgreg
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« Reply #22 on: August 30, 2011, 03:43:29 03:43 »

plz upload circuit diagram then hope so i will help u out because i am professional ups desginer but with out circuit  diagram i can say the resion of mosfet heating to diagnose follow the steps
unplug transformer from mosfet
place load of lamp 24 volt and chek that if ur mosfet heats up or not
plz mention mosfet u r using
if heats up then check that r mosfets r leaky if not then unload lamp load to mosfet's and turn on again ur gate signal now check that with out load on drain and applying signal to mosfet gate r they heating if yes then ur gate drive circuit need to be corrected
if still cool then apply 50% pwm to gate drive circuit it shuld be half the voltage of gate drive circuit power supply and must not greater then 7.5 volts if greater then mosfet will heat even with out load
if gate drive signal wil low to it turn on threshold voltage then that will also cause mosfet heat for example if u r using p75n75 mosfet from st electronics they will stay cool if u apply 200 watt load on them per single mosfet if these all steps r ok then u need to confirm the way u r driving mosfets r they both turned on at same time for 1 microsecond so they will heat up if all things r oky they will work no heating at all hope so this will help u if help then say thanks if u need futher help then u can ask
 and i am feeling very sad that a very simple thing friends r not helpfull to u
left and right
 Sad
ok buddy cheer up now i am available for help  Smiley
« Last Edit: August 30, 2011, 03:47:53 03:47 by shams_iqbal » Logged
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« Reply #23 on: August 30, 2011, 07:03:33 07:03 »

I have found a new design of 24V UPS, please find the attached file and i want ask one question that can i use in place of Power transformer (in the attached file) a normal transformer of 12-0-12 or i have to use high frequency transformer ?

Posted on: July 12, 2011, 04:45:44 pm - Automerged

Here is the file

your both upoladed file are Corrupted please re uploaded
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