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Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 12:42 AM

Dear all,

I wanted to design a Gate driver circuit to drive SCR's connected in anti parallel and use as Static switch for 3phase ups System. can you help me which topology is better to choose and practical circuit which can fit for my application.

thank you.

Karthik H P

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#1

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 2:18 AM

Clicki here for access to an exhaustive research project I recently conducted on the subject.

It's free for the first 1000 hours of viewing, after that please post your credit card information for billing at $10 / hour.

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#2
In reply to #1

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 2:28 AM

Scab!

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#3

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 7:43 AM

I can see how one could use SCR to control the battery charging circuitry but since a SCR cannot be turned OFF I do not see how to use it to produce the three phase power output when running on battery power. I suspect that there are some clever designs using a resonating circuit that does allow SCR to turn OFF. Good luck in your search.

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#5
In reply to #3

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 1:18 PM

Yes, a SCR can be turned OFF. It is required, though, another SCR.

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#6
In reply to #3

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 1:57 PM

A dc conducting SCR is turned off by dumping a capacitor across it to reduce the conduction to near zero long enough for the SCR to shut down. Its a brute force method used in many older Xray machines. They are typically conducting 50A or more at 50+volts, you can imagine the cap energy to quench that SCR.

Quenching circuits to accomodate 3 phases at 60hz will require very large energy waste. Better off to control the current flow through IGBT's.

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#8
In reply to #3

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/22/2014 2:38 PM

Redfred, I believe you are thinking DC. In AC the SCRs will turn off every cycle on their own when the sine wave crosses zero. The gate circuit then has to re-fire them. The OP is asking about a static transfer switch on the AC side.

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#10
In reply to #8

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/22/2014 3:12 PM

Absolutely, 100% correct. I am thinking about DC. Since this thread discusses a UPS which likely includes a DC producing battery, I still believe my point is valid. I presume that this could be an inertial drive UPS system where only AC motors and generators existed. Any inertial drive UPS design company would certainly have engineers that know to look at the recommended application notes of their suitable SCR. The mechanical engineering of such a system is the hard part. The electrical engineering is the easy part.

Somebody that doesn't know how to look for application notes probably intends to use a battery and therefore nearly all of engineering complications will be electrical engineering. As recent threads here show, getting a sine wave output from a DC source using just semiconductor switches is not as easy as many think.

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#4

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/21/2014 8:27 AM

I need to expand my view. I am using the SCRs in my Static Transfer Switches(STS) which switches between UPS and Line. So i needed a help in Driving this SCRs. . .

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#9
In reply to #4

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/22/2014 2:43 PM

Karthikhp12, are you looking to re-invent the wheel here by building your own from scratch? Because there are many companies out there who sell inexpensive gate firing boards used for this exact purpose. Most people who make UPS systems with STS options just use pre-made boards, your sales volume would have to be incredibly large to justify the expense to develop, test and build your own.

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#7

Re: Designing Thyristor(SCR) Gate Driver Circuit.

03/22/2014 12:02 AM

anti parallel? SCR can be used in SCS or transistor mode below hold current.

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