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Rollingblackout

Sat Aug 09 2008, 05:06AM

Registered Member #1524 Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38

Using a modulator on the miniBrute what component is at risk running using a PRF higher then 120-300 hz?

HV Enthusiast

Sat Aug 09 2008, 03:44PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Rollingblackout wrote ...

Using a modulator on the miniBrute what component is at risk running using a PRF higher then 120-300 hz?

The problem is primarily your switching power circuit (i.e. the IGBTs)

What happens is as you increase PRF, but keep pulsewidth constant, you are increasing duty cycle which increases power draw and power dissipation in the IGBTs. This is the 1st order effect. There are 2nd order effects as well.

For the Xenosonic where you do run at PRFs greater than 300Hz - actually almost up to 2kHz, there is a duty cycle foldback circuit. As frequency increases, the pulsewidth starts folding back to maintain constant duty cycle.

But for regular DRSSTC operation, there really isn't much reason to above 300Hz. In fact, i never really run mine above 150Hz.

Also, note that running low PRFs (especially without overcurrent protection) is typically stressing as well. This because the steadystate voltage of the DC bus capacitors is much higher (has much more time to recharge between bursts) and current will tend to increase for the same variac setting than at say 100Hz.

HV Enthusiast

Sun Nov 16 2008, 02:51PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

I have finished construction of minibrute system and am now testing. Just a few little questions to make sure if you don't mind. The IGBTs cost me AUS$70 a piece here, I want to make really sure.

The control board, display board and dc power all check out ok. I am fairly sure that phasing is correct and gate transformer is wired correctly.

1) When it comes to scoping the half bridge board I get very close to the pictures in the book. However the display on the scope is twitchy - it jumps up and down a little. Perhaps my scope is not locking properly. It is a Meguro 1252 35MHz scope. Any comments?

Could be triggering of the scope.

wrote ...

2) At 2us scope range I read a whole cycle as 20us making 50kHz. Is this right?

Not sure what you mean by whole cycle.

wrote ...

3) I am measuring gate to emiter using two probes ungrounded on ADD and with one channel inverted. This is how you make a differential measurment is it not?

Yes. Do not connect the grounds. (You can connect grounds of probes together) And also, be sure the voltage you are measuring DOES NOT exceed the voltage ratings of each probe.

wrote ...

4) I think I am reading opposite phasing of IGBT gates. In this case I should NOT invert a channel, correct?

Each IGBT should be in opposite phase of one another. When on is ON, the other is OFF.

wrote ...

5) when I connect the adv. modulator and the minibrute is not turned on, the 5v LED lights on the display board. I read 1.5v at the ext. mod. input of the self. res. control board. Is this ok or not?

Yes, this is correct. However, you make sure to have power on the control before putting on adv. modulator. I don't believe it wil hurt anything though.

nelsonic

Mon Nov 17 2008, 06:17AM

Registered Member #1612 Joined: Wed Jul 30 2008, 07:08AM
Location: Melbourne Australia
Posts: 5

Thanks Dan

I realized that my sig. gen set at 50kHz not 100kHz. Sorry about that.

Dave Nelson

HV Enthusiast

Tue Nov 18 2008, 07:33PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

nelsonic wrote ...

Thanks Dan

I realized that my sig. gen set at 50kHz not 100kHz. Sorry about that.

Dave Nelson

I still don't know what you are referring to? Is this the output pulses of the bridge, the interrupter signal, etc... ? ? ?

Interrupter signal should be on the order of Hz, not kHz. Output pulses of the bridge should approximate the Fres of your system. (i.e. 100kHz, 200kHz, etc...)

nelsonic

Wed Nov 19 2008, 01:58PM

Registered Member #1612 Joined: Wed Jul 30 2008, 07:08AM
Location: Melbourne Australia
Posts: 5

Ah yes, yes. Signal generator (going to current FB) was originally wrongly set to 50kHz - my mistake. Interupter was approx. 100Hz. Output of half bridge is correct frequency but not at all square like the diagram in the book. Should it be square or rounded off a bit? However, I have now successfully run my minibrute. First run achieved 18inch sparks. I have tested for resonant frequency of secondary to find 185kHz. Reduced primary by one turn and now getting 28inch sparks at current of 400A.

It all seems to be working ok but sparks seem thin.

Setting the overcurrent point has proved difficult. Adjusting R23, I can't get a voltage greater than 5V at U21 pin2. Also current limit cuts in at about 400A, rather than at 500A as predicted. I will keep checking. Any suggestions?

Will increasing the current create fatter sparks?

Also, I have completed the Xenosonic interface. After a long testing/adjusting phase and not seeing any output signal I decided to plug it in and see what happens. It worked! With a signal generator at least. My crappy casio keyboard seems too quiet for the interface.

Thanks again for your support.

d20180

Sat Nov 29 2008, 03:51PM

Registered Member #1828 Joined: Sat Nov 29 2008, 03:00PM
Location:
Posts: 55

Hello, I am starting the build. I built 2 TC's but this is my first solid state. This thread has very helpfull. Does my T1 appear correct? On the resonant driver board, the unmarked positions, have I identified them correctly? Where can you get the IGBT's or is there a good substitute? I have 2 of the HGT1n40n60a4d's, can the HGTG20N60A4D-ND be used? See any mistakes? Please excuse me if I posted the Photos wrong, and let me know how to do it properly.

Thanks

1227973599 1828 FT36701 Resonant Driver Board

d20180

Sun Dec 07 2008, 10:40PM

Registered Member #1828 Joined: Sat Nov 29 2008, 03:00PM
Location:
Posts: 55

So far, so good, or it seemed like a good idea at the time

HV Enthusiast

Sun Dec 07 2008, 11:10PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Wow! That looks great. Very nice work.
Yep, your transformer looks right as far as i can tell. Just remember to have the phasing right when paralleling the primary. Easy enough though.
Not sure about the 20N60's, but i use 30N60s with no problem.

There is also a IXYS equivalent IGBT everyone has been using. See SALE board for more information on this.

d20180

Mon Dec 08 2008, 04:44PM

Registered Member #1828 Joined: Sat Nov 29 2008, 03:00PM
Location:
Posts: 55

"Yep, your transformer looks right as far as i can tell. Just remember to have the phasing right when paralleling the primary. Easy enough though."

Can you explain?

Thanks

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