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Discrete GDT Driver

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zzz_julian_zzz

Mon Nov 21 2011, 10:39AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

hello,

Please see my ISSTC driver schematic below. Kindly give me some feedback on what do you think on my preferred driver. Will this driver work? Also, do you think the enable feature of the circuit will work? How about the feedbacking Circuit? Please, I need some advice on how to implement this kind of Tesla coil circuit. I am trying to avoid using those precious UCC that's why I am to design another way..

If this driver worked, I think this will help a lot to other beginners like me that cannot also have those UCCs..
Please help me.. I am open to modifications to this driver for the development of this circuit.

thank you very much in advance.

Dr. Dark Current

Mon Nov 21 2011, 11:08AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hello,
if the gates output logic-level signals, your circuit will not work. Try this, I have designed this circuit which takes 5 to 15V (max.) input for "high" and <0.8V input for low. A friend has simulated the circuit and it seems to work well.

zzz_julian_zzz

Tue Nov 22 2011, 02:09AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Hi there Dr.Kilovolt,

I was once made this circuit work but just a couple of days., Uhmm,, I think the GDT driving section has a problem, so you're probably right. I will give try your design. thank you very much..

how about the interrupter feature using the NAND(74HC00) gates? Is this correct?
Also, is the 5 volt level logic output sufficient to drive the base of the totem pole or the gate of your BS170(with transistor and FET pair) ?

what do you mean by this?:
if the gates output logic-level signals, your circuit will not work.
-are you pertaining to the voltage and current the NAND gates output can provide?

How about If I use 15 volts logic level? let's say Antenna=> CD4049(HEX NOT)=> CD4011(NAND with INT)=> GDT?
will this correct the problem you pertain?

Also, the totem pole and FET pair I have designed is a INVERTING GDT driver., that is why I used NAND.. If I used your design(which is NON-INVERTING), will this cause a problem?

thank you for your input DR.Kilovolt =).. I hope for your fruitful reply again, thanks..

Dr. Dark Current

Thu Nov 24 2011, 11:45PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hello,
I think the interrupter will work.
The 5 volt signal is sufficient to drive my circuit.

I was referring to that the gate driving circuit you posted, needs a full input swing from 0 to Vcc to operate properly.

Well you can use 15 volt logic, but these are usually slower than their 5V counterparts.

It doesn't matter if the drivers are inverting or non-inverting in this case.

zzz_julian_zzz

Fri Nov 25 2011, 02:51AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Sir, you said:
It doesn't matter if the drivers are inverting or non-inverting in this case.

Will the output is the same function as the inverting?in your circuit, both non-inverting drivers before primary side of the GDT will stay HIGH, when the interrupter says LOW.. please see my drawing(sorry for bad quality

will this make the switching devices in the halfbridge in shoot through condition because of the BOTH ON-STATE condition?

what are the possible substitute for bs170 can i just use 2n7000 or just irf640?, for bc337 can it be bd137? and how about the bat65? can i use 1n5819?

what do you think with the circuit in (picture no.2)
will this work as gdt driver?

also,in your circuit, is the single trasistor (bc337) capable in producing large currents like the totem pole(npn-pnp)? is the output of your circuit rail to rail?

Thank you again for all the information you are willing to share.. thank you very much..

Dr. Dark Current

Fri Nov 25 2011, 11:03AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Julian,
if both gate drivers connect the primary to the same supply rail, the gates are LOW. It doesn't matter if the GDT primary is shorted to gnd or vcc. The GDT prohibits both gates to be HIGH at the same time, from design.

The BS170 was chosen because of very low gate capacitance (25 pF) which is the same as TC4422 driver, and to allow it to be driven from 5 to 15 volts for the high input.
The 2N7000 FET should work well.

The BC337 can produce 0.8 amp output current, which is more than enough to drive the two IRF FETs with low gate capacitance and charge. You can use any NPN transistor, which is fast enough and has at least a 0.5 amp current rating.

Yes I think you can use a 1N5819. Its capacitance could be a little problem, but I guess it won't matter.

As for the circuit you posted: It should kind of work, but you must use reverse diodes on the transistor and there will be a pretty large saturation voltage and with the reverse diodes this results in a large "dead voltage region" (for a lack of better words) which might be seen as steps on your gate waveform.

zzz_julian_zzz

Sun Nov 27 2011, 09:09AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I will give try to your design Dr. KV, I'll post ASAP the result of the said circuit. I will be using 2n7000 mosfet in place of bs170, and bd137(1.5 Amp) in place of bc337(.8 Amp). This would work right?

Also, the circuit of yours outputs a rail to rail ? and Uhmm.. how about the feedback? is there NO problem using an antenna (8 inch 24 awg) then feed it to (100nf) cap => 1n4148 diodes (5v) =>then to 74hc14? can you give me some tips to get decent feedback with circuit?

Thank you very much Dr. KV.. tonight I will copy your design and solder it on a neat board =). thanks again, And i hope if I encounter any problems with the suggested circuit, you will be there to help me find the problem =P thanks a lot..

Dr. Dark Current

Sun Nov 27 2011, 10:04AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hi, yes the BS170 will work. BD137 could be a little slower than the BC337 but I think this will be ok.
Yes the output is rail to rail.

If you want to use antenna feedback without an interrupter, you need a start up oscillator. For this you connect one HC14 gate as a hysteresis oscillator and feed this through a 100k resistor to the antenna and input of another gate.

zzz_julian_zzz

Mon Nov 28 2011, 03:01AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Hi DR,

I am not planning to do SSTC without an interrupter,
What I meant here:

"antenna (8 inch 24 awg) then feed it to (100nf) cap => 1n4148 diodes (5v clamp) =>then to 74hc14",

IS: Just for assurance, Is my existing schematic (the very first post) of feedbacking circuit will work as intended? of course, the output will be 74HC00 NANDED(because of availability issue) to interrupter.

Will this circuit work well?

Thank you again Dr. KV

Dr. Dark Current

Mon Nov 28 2011, 09:45AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hi, sorry I forgot what you said about the interrupter, guess I'm doing too many things at once.
I think the circuit should work if you get all the phasing right. The circuit is similar to Steve Ward's mini SSTC.

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