Mr. BaWa,
Here is the schematic for my DC-dc converter
I however used 4 Mosfets ie. I paralleled one with the high side Mosfet and the other with the lowside Mosfet
Here is the SPWM section I'm using that I found from another site:
For the signals from the MCU as we discussed in previous post that the SPWM should go to the high-side MOSFETs and the fundamental frequency to the low side MOSFETs so that diagonal MOSFETs switch on at the same time so not shown in the diagram
signal A should go to Q4 instead of Q1
signal B should go to Q2 instead of Q4
signal C should go to Q3 instead of Q2
signal D should go to Q1 instead of Q3
Further,
When I remove the heat sink off my MOSFETs (N.B.all four FETs were connected to one heat sink) and connect the 180Vdc DC link or DC bus to the drains of the 2 high-side FETs, the noise stops from the ferrite transformer as mentioned earlier but the leds in the circuit (that are used just to indicate the presence of current) and even my laptop screen starts to flicker and when I measure across the cap parallel to a 20W bulb I get about 15VAC.
Whats wrong here???
this is a push pull topology and the mosfet shown in 1st figure all are low side .Kryptone said:I however used 4 Mosfets ie. I paralleled one with the high side Mosfet and the other with the lowside Mosfet
yes I used pushed pull for dc-dc converter I just paralleled the other two MOsfet to try and acheive more power. The heat sink was actually for the h bridge I did not use a heat sink for the FETs in the dc-dc stage.I took the heat sink from an old computer SMPS and yes it has insulating pads on it.
So you are saying that for the push pull dc-dc converter that I am using both are low side?? I'm confused I was sure one is high side and the other low-side.
So could that be apart of the problem but it works giving me 180 Vdc across the capacitor of the LC filter. The capacitor is 10uF, 400V and I'm not sure of the value of the inductor.
It should be AC, not DC.180 Vdc across the capacitor of the LC filter
I think Kryptone is talking about DC DC stage output filter , so it should be 180v DC there , but the problem is ,when he connect a Load to DC DC stage output ,the voltage drops significantly , which means that the DC DC stage is not working properly.ALERTLINKS said:It should be AC, not DC.
let me do some calculations for you, you have connected a 75 watt 110v rating bulb at the output ,so the resistance of filament of the bulb is 161.3ohms(using ohms law ). and the converter output voltage is 180vdc .so the bulb will consume approx (V/R) i.e 180/161.3 =1.11 ampere.Kryptone said:but then again it didnt work with the 75W bulb either so perhaps impedance of the LC filter resonance cld be a problem or mabe the transformer is damaged because I supply about 14V from a power supply to the dc-dc converter and the voltage drops to about 12V and I know its the transformer because when I disconnect it the voltage is 14V as provided and when I connect it the voltage drops slightly.
I think Kryptone is talking about DC DC stage output filter , so it should be 180v DC there , but the problem is ,when he connect a Load to DC DC stage output ,the voltage drops significantly , which means that the DC DC stage is not working properly.
let me do some calculations for you, you have connected a 75 watt 110v rating bulb at the output ,so the resistance of filament of the bulb is 161.3ohms(using ohms law ). and the converter output voltage is 180vdc .so the bulb will consume approx (V/R) i.e 180/161.3 =1.11 ampere.
now come to the transformer input current, as you know the relation
[ i1 / i2 = v2 / v1]. where v2 should be 180, v1 should be 12 and i2 is 1.11 , so if you calculate i1 . it will be 16.6 ampere , so you must connect the input of DC DC stage to a BATTERY or a power supply capable of providing atleast 16 ampere.
i doubt if your power supply can provide this much of current at 12v , so i strongly recommend to use a 12v battery (of ups or inverter).
also check the gate voltage of the mosfet , and let me know .
It should be AC, not DC.
Inverter have different working sections. Each can be tested separately. First you produce 180V DC_bus. This section, you say is working. Don't connect h-bridge for now. Dc bus has its own filter capacitor, from where h-bridge will be connected.
Test DC converter if it can deliver the full wattage by connecting load, such as bulb, your soldering iron etc. Check the voltage drop with increasing load. Let it operate for few minuets If it works ok, the ferrite transformer and FETs does not heat excessively.
Now, the AC converter, only connect micro controller and FET driver section to 12V DC and check with oscilloscope or multi-meter for gate signals. Are they the same as expected.
Now connect 12V-DC to h-bridge, not 180V, and check if 8V-AC on H bridge output. You can remove LC-filter to see if it is not causing problem. Most probably your h-bridge has a short circuit. It should not draw current from 12V supply, when there is no load on its output. Monitor current, it draws with multi-meter, putting it in series with +12V.
If all works well now you can connect with 180V-DC but put the bulb in series with +180V and +ve wire to hbridge. Bulb will light up if there is short in it. This will protect mosfets of hbridge and DC converter(you have already made smoke out of ferrite transformer). Check for 120V-AC on hbridge output. Now you can remove bulb and connect directly to +ve 180V. Put load on hbridge output. Check if it supports full load and FETs don't heat-up. Now you can check output waveform with different loads.
which stage are you talking about ?i was talking about DC DC stage . i have already said that there is no high side mosfet configuration in push pull, so how have you written the high side mosfet configuration . ?Kryptone said:For High side
Drain wrt Gate 11.8V
Drain wrt GND 11.8V
Drain wrt source 7.6V
i think u havn't gone through post #27 , i have clearly calculated the input power supply configuration.Kryptone said:At the input of the dc-dc converter, I am using a 12-0-12 V, 2A transformer
Follow the instructions given in post #27 .Kryptone said:Could the value of L or C need to be changed to drop the 50 KHz through the transformer to a much lower frequency?? could this cause flickering of the bulb when connected in series between +180Vdc and the drain of h-bridge???
which stage are you talking about ?i was talking about DC DC stage . i have already said that there is no high side mosfet configuration in push pull, so how have you written the high side mosfet configuration . ?
i just wanted to know the gate to source voltage of mosfet of DC DC converter stage ?
i think u havn't gone through post #27 , i have clearly calculated the input power supply configuration.
Follow the instructions given in post #27 .
u r right there is no need of bootstrap circuit , the schematics shown in post # 22 ,https://obrazki.elektroda.pl/8827873100_1396903703.html is practical . so you can make it as it is ,and dont add bootstap circuit in it ,,,
and also your power supply current rating is not sufficient ,so if u manage to make the circuit , u can't drive a 75 watt bulb trhrough it . Use a 12v battery of capacity > 7ah atleast for testing purpose.
and the picture there of h-bridge.The dc-dc converter worked and now I am on to the SPWM section where I am using the ATmega16 to generate the SPWM signals .
i have never tried to use IR2110 only for low side drive , its a HIGH LOW side driver IC , you can try it ,,,one more option for you ,in your pcb you can bypass the input pin to the output pin of IR2110, and remove the ic , after doin this tell me the gate to source voltage ?
and i will also suggest some low side driver ic or totem pole driver between sg3525 and mosfet bank, because u r using 2 mosfets in parallel , so there might be a possibility that SG3525 cant provide enough current to drive the mosfet gate . to turn the power mosfet fully ON ,ensure that Vgs should be greater than 8V.
It is used on dc link to minimise the spikes and current ripples, it should be placed near your power stage.Kryptone said:Also, what is the purpose of the 2200uF capacitor connected to the centertap of the ferrite transformer?
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