Half bridge dc-dc circuit with PIC16F1827

[jean12]

Hello there, I am in trouble with my circuit I am designing a dc-dc half bridge which has to use MOSFET IRF3205 for controlling the high frequency transformer which step-up the dc voltage, but I created the controlling signal with PIC16F1827,my signal has a dead time of 15us; unfortunately when connecting the 12VDC battery the MOSFET are becoming very hot, the heat sinks are placed.

can you please help me to think on any other think I can do?

Thanks.

Please help.!!

 

[jamespond]

Please post your schematics. I think from your words the MOSFET not fully open or close. Check the signal on gate.

 

[jean12]

I am not able to give you the circuit becuase my proteus is does not has the components I am suing,but I have the PIC 16f1827 whith which I am outputting a square wave which passes into the driver ICL7667 and then those the output of the drive go to the gate of the MOSFET ,but the MOSFET are becoming very hot,so I am asking if there is any isolation required ?
If yes is it possible to use for example 6N135 or 4N25 becuase those are the ones I have ;if yes how would be the connection of those optocoupler mainly the Emitter pin where it has to be connected?

Thanks.please help.

 

[nick703]

ok then try this type connection of opto coupler
https://www.google.co.in/imgres?sa=X&biw=1024&bih=629&tbm=isch&tbnid=Lo2Egz0Y3ENKVM:&imgrefurl=http://kaituanui.com/elect_comp-notes-1.htm&docid=WCBX1gTtGyAROM&imgurl=http://kaituanui.com/pics/ele-comp-howto-use/driving_irf_mosfets_via%2525204n25.gif&w=2196&h=1128&ei=tTysUs3dIcymrQeu1IGwDA&zoom=1&ved=1t:3588,r:7,s:0,i:99&iact=rc&page=1&tbnh=142&tbnw=259&start=0&ndsp=11&tx=108&ty=81

 

[jean12]

Hello,nick703 I don't see the other connection for the diode in the optocoupler one is on 5V where will be the second terminal?I don't see well what is written there?

Thanks,please help.

 

[nick703]

hey Jean12 Opto coupler is Ic which has a 6 leg Right in this circuit diagram clearly describe that This Is inbuilt function like Diode and Transistor u just connect your mcu signal to pin no 2 of 4n33 (4n25) type.

 

[jean12]

and what about pi 3?of that optocoupler will it be connected to the ground of the secondary side on pin 4 as all are on the ground??

Please help,thanks.

 

[FvM]

I am not able to give you the circuit becuase my proteus is does not has the components I am suing,but I have the PIC 16f1827 whith which I am outputting a square wave which passes into the driver ICL7667 and then those the output of the drive go to the gate of the MOSFET ,but the MOSFET are becoming very hot,so I am asking if there is any isolation required ?
If yes is it possible to use for example 6N135 or 4N25 becuase those are the ones I have ;if yes how would be the connection of those optocoupler mainly the Emitter pin where it has to be connected?

It's completely unclear how you are driving a half-bridge with ICL7667. If you want effective help, you should at least sketch the implemented circuit topology,

 

[jean12]

No you know ICL7667 is a MOSFET drive so the output signal from the PIC they are passing through ICL before going to the gates of the MSOFET.

Here is the circuit.

Thanks,please help.

 

[FvM]

It's a transformer push-pull output stage, not a half bridge.

You didn't yet tell about test conditions, e.g. behaviour with different loads. So we can only comment the problem quite general.

There are several possible reasons, why excessive heating of the output MOSFETs can occur
- core saturation due to wrong transformer design
- core saturation due to imbalance ("staircase saturation")
- avalanche breakdown of transistors due to overvoltage caused by transformer leakage inductance
- losses caused by unwanted switching due to bad circuit layout

You should not post uncompressed bmp files, use gif or png format.

 

[jean12]

This is a dc-ac I am repairing meanwhile the transformer is well designed,because its industry made control circuit was working perfectly without heat,so I want now to design its control circuit,the first was working at 25KHz that's why I used the PIC and design an oscillator which is giving the same with this.

But the MOSFET are just becoming hot when I apply the gate signal without load.

Please help,Thanks.

 

[FvM]

Watch the gate and drain waveforms with oscilloscope.

 

[BradtheRad]

It is possible you are getting spikes, generated by the transformer when each mosfet switches off.

Did you attach any kind of snubber?

I once used the same topology making a homebrew inverter. It worked okay with a light load, but as soon as I increased the load, the mosfets heated up.

Turned out there were severe spikes on the waveforms through the mosfets. The spikes were generated by inductive action in the transformer, as the mosfets switched off.

I remember trying to get rid of the spikes, by attaching small capacitors at different places. I might have succeeded if I had known more about snubber networks.

 

[jean12]

So what advice are you giving me on this point?

How do you think I can remove those spikes,I used the 22nF capacitance at the output of the Drive;what do you think should I do?
Thanks.

 

[FvM]

How do you think I can remove those spikes

Do you see "those spikes"? You didn't yet report actual measurements.

 

[jean12]

See the codes

#include <16F1827.h>
#DEVICE ADC=10
#fuses HS,NOWDT,NODEBUG,NOCPD,NOLVP
#use delay(clock=4000000)

void main()
{
set_tris_b(0x00);
while(1)

{
output_high(PIN_B0);
output_low(PIN_B2);
delay_us(40);
output_low(PIN_B0);
delay_us(10);

output_low(PIN_B0);
output_high(PIN_B2);
delay_us(40);
output_low(PIN_B2);
delay_us(10);


}

}

I am using for generating the square wave at 31KHz,the figures I am getting are really good after filtering wth the 22nF capacitance at the output of the PIC.

 

[FvM]

The generated frequency according to the code is 10 kHz, not 31 kHz.

I don't see where you would use 22 nF capacitors and why.

 

[jean12]

The generated frequency according to the code is 10 kHz, not 31 kHz.

I don't see where you would use 22 nF capacitors and why.

We have a delay of 40us which gives the frequency for every signal and the 10us I used is for creating a dead time,don't you see it??

Please help.

 

[jean12]

Hello,here is the graphic I am getting which is applied on the gate of MOSFET.

Please help.

 

[FvM]

Do you actually have overlapping gate voltages?

O.K., I see that ICL7667 is an inverting driver, you are generating your control signals with wrong polarity.