(igbt halfbridge) circuit problems, i'm stuck

[killivolt]

Having issues I'm not sure if it's oscillating or not I've checked all the connections and their ok, maybe to parasitic or something. The GDT is wound correctly. I guess I'll check the I/O next on the GDT.

I checked and it's wired correctly, now I just need to check to see if it's oscillating at 30kHz

 

[killivolt]

Ok, I messed up on the outputs. I'm going to have to go back over the board again.

Edit: I found it, when I was scoping.

 

[killivolt]

Ok, I think I have at least 20kHz and the chip hasn't failed or anything. A bit warm doesn't sizzle but, the spit quickly evaporates.

The waveform is pretty ugly though.

Any thoughts, help, Ideas? Here's pics of the scope. I'm probing both gates of the Mosfets. Here is the schematic I built..https://adammunich.com/oldstuff/Plasma_Speaker_2_files/schem.png

kv

 

[jpanhalt]

Are you using Mosfets or IGBT's?
Can you post the schematic?

Source 1 and 2 on both gates of the Mosfets.

"Source" could mean your probe is attached to the gates, but it is also the name of a pin. Where are your probes attached? Where is the ground clip attached?

Regards, John

 

[killivolt]

Are you using Mosfets or IGBT's?
Can you post the schematic?

Here's the schematic.
https://adammunich.com/oldstuff/Plasma_Speaker_2_files/schem.png

Source" could mean your probe is attached to the gates, but it is also the name of a pin. Where are your probes attached? Where is the ground clip attached?

Regards, John

Thank you John, I'm such a noob.

I did mean to say I have a GDT I wound myself. 2.5mm core 3 raps 14 turns, I'm trying to drive it with 20kHz ocillation from SG3525AN , here is what waveform is supposed to look like, I'm probing at the Gates of the Mosfets I'm using the ground on the board, I don't know if I'm scoping it correctly or not I'm just not sure where to start?

Thank you for your reply,

Sincerely,
kv

 

[shortbus=]

Hi killivolt, maybe a dumb question, but why use a gate drive transformer? The SG3525 is made to drive mosfet gates directly. Don't quite understand the use of the GDT.

With the GDT the gates will be slow to shut off without a pull down resistor on the gate to ground/common.

 

[killivolt]

Hi killivolt, maybe a dumb question, but why use a gate drive transformer? The SG3525 is made to drive mosfet gates directly. Don't quite understand the use of the GDT.

With the GDT the gates will be slow to shut off without a pull down resistor on the gate to ground/common.

Well I'm told from the "Instructables website this guy built this, and he says" Qoute: (There is a Gate Drive Tranformer. What this does is provide an isolated gate drive for the upper mosfet preventing it from dying, and it is required for the circuit to work properly.)
(BTW) It's a Plasma Speaker.

I did read the data sheet on the SG3525 or at least. (As much as I could understand anyway) It shows the SG3525 arrangement for 2 Mosfets driven directly, I noticed it shows the pull down resistors.

As for the Gates I'm not an Engineer, but there is (2) Zener's back to back between Gate and Source ? I'd like someone to explain that one to me

Anyhow I'll work on it this week and try to VeroBoard this and make a new GDT.

While doing this I read somewhere, that you don't want the Mosfets to far away from the chip, mine are about 3 inches away and I have the return of the center coil coming back to the chip via underneith the GDT.

The GDT is about 1/4" off the main board on its own board, still I knew this might become a problem.

I'll work on it, and give it another go.

Thanks for your reply's

Regards,
kv

 

[ChrisP58]

The gate drive transformer is necessary because the source pin of the upper mosfet is not at ground.

But I think there is a problem with the transformer driver. Pins 11 and 14 of the SG35245 are both emitters. You are putting +12V alternately into each side of the transformer, but there is no ground node to complete the current path.

The easiest way to fix thast would be to add a center tap to the GDT primary.

 

[killivolt]

The gate drive transformer is necessary because the source pin of the upper mosfet is not at ground.

But I think there is a problem with the transformer driver. Pins 11 and 14 of the SG35245 are both emitters. You are putting +12V alternately into each side of the transformer, but there is no ground node to complete the current path.

The easiest way to fix this would be to add a center tap to the GDT primary.

First off, I can't believe your only 10 or so miles from me, I'm in Orem and grew up in Provo. Thank you for your reply.

So, can you config the Transformer for me, I'm not an engineer, I'm just a noob. I like putting things together and making them work, sort of beating them softly into a powder puff with compliance

I totally enjoyed my day's off working on this, I really want to build this and make it work well and give them as gifts to 2 of my friends. Both are well educated and schooled on electricity and the nasty's of it, if on the wrong side of the flow.....wink.

A schematic would be really nice, I don't care what it looks like, hand drawn, really I would appreciate it. I will need to take care of the signal and make the right waveform.

Thanks, Chris

Regards,
kv

Edit: Oh, and I did see a center tap, on another Plasma Speaker but, the Chip was driving directly. No, GDT. I can't see how I could implement this? but I will try anything.

FYI, I bought at least 10 of everything..., just for this reason.

Edit:Edit: Now, this reminds me of another person trying to complete this project. They had completely lost the top Mosfet and couldn't get it to work right. (That explains a lot)

 

[killivolt]

The gate drive transformer is necessary because the source pin of the upper mosfet is not at ground.

But I think there is a problem with the transformer driver. Pins 11 and 14 of the SG35245 are both emitters. You are putting +12V alternately into each side of the transformer, but there is no ground node to complete the current path.

The easiest way to fix thast would be to add a center tap to the GDT primary.

Ok, I thought about this morning and of course Googled, I can't find anything but, experimental stuff or patented things relating to a Driver and GDT Center Tapped?

I'm very confused by your post and can't think of how you would implant it this on the primary.

Sorry, this maybe something big and new, but I can't find anything solid on it, past or future?
kv

 

[ChrisP58]

My office is in Orem, so we're not far apart at all.

Here is a very rough schematic to show the basic concept

The two NPN transistors are internal to the PWM chip.

When Q1 turns on it will pull A low, B will swing up to +24V, The upper mosfet will see a negative 12V pulse, and the lower mosfet will see a positive 12V pulse.

When Q2 turns on, everything swaps state.

 

[killivolt]

My office is in Orem, so we're not far apart at all.

Here is a very rough schematic to show the basic concept

The two NPN transistors are internal to the PWM chip.

When Q1 turns on it will pull A low, B will swing up to +24V, The upper mosfet will see a negative 12V pulse, and the lower mosfet will see a positive 12V pulse.

When Q2 turns on, everything swaps state.

I think I'm beginning to get this, Thank you so much for your help. I'm sure you will be helping a lot of other poor souls who will or have attempted this circuit only to be disappointed.

I also work at UVU, living just 3 minutes from work.

Please, if you don't mind me asking, are the diodes still needed in the circuit?

Second, instead of the original (3 raps and 14 turns,) I now have (4 raps and 14 turns) or am I just tapping the center control at the 7 turns, still keeping the original turns ratio and just 3 raps?

This is the part I just couldn't get into my head, again, I'm not an engineer.

I'm just a hobby tinkerer with ("very basic") Electronic knowledge.

Regards,
kv

Edit: I think I should add that to my Signature.

 

[killivolt]

My office is in Orem, so we're not far apart at all.

Here is a very rough schematic to show the basic concept

The two NPN transistors are internal to the PWM chip.

When Q1 turns on it will pull A low, B will swing up to +24V, The upper mosfet will see a negative 12V pulse, and the lower mosfet will see a positive 12V pulse.

When Q2 turns on, everything swaps state.

After thinking......Here is the Original Schematic. ..https://adammunich.com/oldstuff/Plasma_Speaker_2_files/schem.png

If I tie to a center tap 3 raps 14 turns tapping at the 7 turn. I would just tie it in parallel to the 12v rail "of the Regulator" Correct?

 

[ChrisP58]

Each half of the primary should have 14 turns. Only the winding on one side of the CT is driven at a time, so each side needs to have the same turns as each secondary if you want a 1:1 ratio.

The diodes as shown in the original schematic will cause a short since the un-driven end will fly up to twice the CT voltage. Think of the primary like a teeter-totter with the CT being the pivot.

 

[killivolt]

Each half of the primary should have 14 turns. Only the winding on one side of the CT is driven at a time, so each side needs to have the same turns as each secondary if you want a 1:1 ratio.

The diodes as shown in the original schematic will cause a short since the un-driven end will fly up to twice the CT voltage. Think of the primary like a teeter-totter with the CT being the pivot.

Thank you.
kv

 

[killivolt]

So, I rapped the GDT. Looks good so far.

 

[killivolt]

Update, here is my Schematic of the Plasma Speaker ....... **broken link removed**

I started over, no longer using strip board, just copper padded breadboard.

I have re-aranged the GDT and Control Chip Laying them out to closer and inline with the Power FETS, less chance of parasitics.

The GDT is now a center tap (4 windings 1/1 at 14 turns 22g.) instead of the Authors 3 windings. I will attempt a push pull tapping the center to the 12v rail. I will pull out the diodes, but leaving the Zeners.

I will be driving the GDT as if driving the Power Mos's directly. I don't know if I should leave the MKP in or out or just add another one, on the second winding of the primary?


Here the new Layout of the Board..

 

[killivolt]

So, with much help from the forum, and creating a Spice Model to keep me from building another disaster, I need some advice.

Will this work in the real world, or or do I need to pick another circuit.

LT Spice Model, I have no idea how to run it, if you could try it and tell me if it does work. Thank you.