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high current 0 to 40 volt pwm and v-reg power supply

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LAN_403

Neet Studio

Tue May 22 2012, 02:49PM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
Location:
Posts: 86

GDT is a topic that I would defer to the experts on 4hv. I barely only know enough about power supply to keep my head above the water. ;)

SSTC Gate Drive Transformer (GDT) Design Guidelines

Gate drive transformer

Solid state tesla coils - general notes

Also see the URL on bottom of page.

brandon3055

Thu May 24 2012, 06:02AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

i just tested the circuit with one mosfet and the voltage control works but when i draw any current the voltage drops i think its becaus the gate voltage is to low but unfortunitly i dont have an ocilloscope so i cant test it the gdt also meanes the duty cicle cant get down to 1% wich means the current will be limited the scematic below is my exact setup

B.T.W do you know the max speed of an opto isolator becous altho it wouldnt be perfect i might be able to use one to replace the GDT (i realy hate GDT,s)
]tl494_power_supply_2.zip[/file]

teravolt

Thu May 24 2012, 06:12AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

does the transformer voltage or the raw dc dip when you put a load on it

brandon3055

Thu May 24 2012, 06:19AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

the output drops the input dosent change (the test voltage was 15v)
edit: the current draw os only about 1A pluse the 10R output resistor

Neet Studio

Thu May 24 2012, 05:01PM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
Location:
Posts: 86

>do you know the max speed of an opto isolator

That depends on which opto isolator part you are talking about as there is a very large range.

For the old diode to transistor, it is usually listed under AC Characteristic section of the datasheet and only shows a typical value (i.e. it is just a courtesy to the customer to give him/her an idea, not tested/nor guaranteed). From the 3-4 datasheets which I have in my parts bin, it is around 2-5us.

If you want it to be fast, there are H-bridge drivers or high side driver specifically designed for this. The low voltage one (limited by the production process) typically internally uses level shifting. The high voltage ones uses 2 separate circuits with some capacitive coupled signals across the isolation barrier to trigger a Flip/Flop for the high side driver.

Reading material:
Design And Application Guide For High Speed MOSFET Gate Drive Circuits

A Guide to Designing Gate-Drive Transformers - Ferroxcube

>when i draw any current the voltage drops
You are running the PWM with an open loop. With a (properly designed) closed loop, the feedback would cause an adjustment in the duty cycle to compensate for the change in the output voltage.

brandon3055

Fri May 25 2012, 07:26AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

quick update i have just spent 2 hours building and rebuilding the circuit on my breadbord and i finaly got it working and i have ateched a schematic of the test setup below i still need to increase the gate drive current but the optocupler works grate and i am getting full vultage regulation from around 2v up to 40v the biggest problem i need to sort out befor finalizing mi circuit is the vultage control is to steep meaning the first 75%f the pot is about 2-20v and the vultage rizes realy fast over the last 25% (but it is still regulated)
any ideas?
(the duty cicle controle was copyed from uzzors multy purpose inverter so im not shore how it works but it dose)
]tl494_power_supply_test_setup.emf.zip[/file]

Neet Studio

Fri May 25 2012, 12:50PM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
Location:
Posts: 86

>to steep meaning the first 75%f the pot is about 2-20v and the vultage rizes realy fast over the last 25%

First off, the way you setup the 10K pot. When you are at the lowest voltage setting point, the output will violate the absolute maximum rating.
VI Amplifier input voltage: VCC + 0.3 V !!

Are you using a log scale pot or linear pot?

You do realize that the way you connect the optoisolator means that there is no current limits going into the device. Transistors and the LED in optoisolators works like diodes. That's why I have resistor in series.
MOSFET driver have CMOS input, that why I recommend to have pull down on them and no series resistors.

If you read the references, there should be enough theories to get you going. Might want to sit down, read the datasheets and do designs instead of blindly hooking things up and see how they work. That's what I preach and practice.

I spent about 2 months design/simulation before I even do the schematic capture (less than 1 week) and about 3 weeks in the lab for a "hard" project that was way over my head. It went through mechanical/thermal design, layout, proto run and pass regulatory certification by an external lab all on first rev. That was about the same amount of time the other guy who supposedly have more "experience" spent tinkering in the lab.

I'll do a proper circuit review for a proper design, but my time is wasted in correcting every time you are tinkering. I may come back to this thread in a few months or never.

brandon3055

Fri May 25 2012, 02:13PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

If the 10k you are referring to is the voltage adjustment that must have been a typo it is actually a 50k and as I said earlier the way I set up the optocupler was just for a basic test I will post my results when everything is 100% complete but as you said it will probably take a while thanks for all your help

Edit: its almost finished I should have it dun sume time tomorrow the only thing I haven't figured out yet is how to fix the voltage adjustment any ideas? atleast it will have good low voltage adjustment LOL
Also I don't have a proper schematic yet I haven't had time to make one yet but I will when it is finished

brandon3055

Sun Jun 10 2012, 02:10AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

If anyone's still watching this thread I am planning to post it in the project forum when i have installed all the bells and whistles over current protection voltmeter sum smaller liner regulators cooling fan exetra but it will take me a while to get all the parts I need so here it is fully operational running loads between 15A and 40A the only thing that overheated was the output inductor and of cors the test load as for the problem with the voltage adjustment I was able to make that less of a problem by adding a high and low range but it is still a bit of a problemb

BTW the display is dull due to a problem with the isolated power supply not the load being draw

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