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Registered Member #1415
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1. How does varying the PRF, Pulsewidth, and Duty Cycle, affect the spark and drsstc system? 2. Are these three changed to vary the sound quality and tone? 3. Is the (pulse repetition frequency) talking about AC current (as in 60 cycle) or the amount of times the system is turned on and off. 4. Also, what exactly does the interruptor do, and what is its purpose?
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I know nothing about drsstc's but the interrupter does what the name suggests. It interrupts the output so you basically have the oscillations turning on then off. The purpose? Well it saves power,therefor improving efficiency. If you interupt it at high enough frequency it looks constant but it will use much less power. I dont know were the interrupter is placed but i know it just cuts the power off to whatever frequency it is set.
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SteveC wrote ...
1. How does varying the PRF, Pulsewidth, and Duty Cycle, affect the spark and drsstc system? 2. Are these three changed to vary the sound quality and tone? 3. Is the (pulse repetition frequency) talking about AC current (as in 60 cycle) or the amount of times the system is turned on and off. 4. Also, what exactly does the interruptor do, and what is its purpose? Thanks
1. PRF will increase how many arcs are occurring per second. It also affects the sound of the arc. If you are running at 100Hz, you will hear a 100Hz audio tone. However, remember for a fixed pulsewidth, increasing PRF increases duty cycle, and hence, power levels, and stress on the components.
2. Pulsewidth is the time the coil is on for each burst. Short pulsewidths result in little or no arc, up to a point where maximum arc length is reached. Above that, the arcs just get real thick and draw lots of power.
3. Duty cycle is simply the percentage of ON time (burst) vs. OFF time.
4. PRF creates the audio tone frequency. Pulsewidth will make a tone sound "fuller", but increases power levels.
5. An interruptor, or a "modulator" which is the technically correct term (or at least industry correct term) is simply the controller which turns the DRSSTC ON or OFF. It would be synonomous with "grid modulator" (for example) which is used to turn RF tube ON or OFF. DRSSTCs are almost never run CW, so you need to modulate them ON or OFF at some specified PRF and PW. This is what the interrupter does.
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Thanks for the replies, but I must keep the questions coming...
Is the interruptor turning the entire system off after each individual spark is made. So if you had a prf of 100Hz, then after each spark the interruptor would turn the entire system off one hundred times? Or am a making this to complicated, and the interruptor is just used as an on/off switch to start and stop the system for longer periods of time.
To Dr. Shock: I bought your book from LuLu and I am planning on building your first generation drsstc
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SteveC wrote ...
Thanks for the replies, but I must keep the questions coming...
Is the interruptor turning the entire system off after each individual spark is made. So if you had a prf of 100Hz, then after each spark the interruptor would turn the entire system off one hundred times? Or am a making this to complicated, and the interruptor is just used as an on/off switch to start and stop the system for longer periods of time.
If you had a PRF of 100Hz, and a pulsewidth of 100us, then your coil would be ON for 100us, and then off for 9.9ms. (Period of 100Hz is 10ms) Yes, the interrupter is just an ON/OFF switch.
wrote ...
To Dr. Shock: I bought your book from LuLu and I am planning on building your first generation drsstc
Thanks. My recommendation however, would be to use a 2nd Generation design. The design really isn't any more complex, and is much more reliable and better working as it utilizes primary current feedback, as well as synchronized shut-down and overcurrent protection.
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Let me see if I am understanding this correctly...
If a drsstc has a prf of 100Hz, then the igbt's are turned on 100 times a second. During each 100us segment, do the igbt's allow current to flow into the primary once, or do they do it at the resonant frequency of the secondary coil. I am thinking they switch current at the resonant frequency of the secondary coil (I believe this is where the "Dual" or "Doubly Resonant" comes in. I am confused about how many times the ibgt's are actually switching, and how many times a tank circuit is formed.
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SteveC wrote ...
Let me see if I am understanding this correctly...
If a drsstc has a prf of 100Hz, then the igbt's are turned on 100 times a second. During each 100us segment, do the igbt's allow current to flow into the primary once, or do they do it at the resonant frequency of the secondary coil. I am thinking they switch current at the resonant frequency of the secondary coil (I believe this is where the "Dual" or "Doubly Resonant" comes in. I am confused about how many times the ibgt's are actually switching, and how many times a tank circuit is formed.
100us is the time the DRSSTC is turned ON. When its turned out, a burst of length 100us is output into the primary coil where the carrier frequency of the burst is the resonant frequency of the DRSSTC. For example, if my DRSSTC has a resonant frequency of say 200kHz, then for each time the DRSSTC is pulsed on, you get a burst of 200kHz pulses from your output bridge. For 200kHz, this would amount to approx. 20 cycles per burst. The carrier frequency is determined by the current feedback transformer.
So for a 200kHz resonator, 100Hz PRF, and 100us pulsewidth you'd get:
(ON for 20 5us pulses) OFF for 9.9ms (ON for 20 5us pulses) OFF for 9.9ms etc.....
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Thanks.....Makes Perfect Sense
I see how even though the igbt's are switch at the resonant frequency, they only complete the action 20 times, because 100us is a very short amount of time.
I'm assuming that people make drsstc's have low secondary coil frequencies, like in the 40 or 50KHz range, because it lessens the stress on the igbt's. Decreasing the pulsewidth would also allow to igbt's to switch less.
I was curious about the optimal shape of a primary for a drsstc. I have heard that a flat spiral is not the best, but what about a conical vs. an upright. I have seen one of Steve Wards Coils (the one that plays super mario brothers on you tube) and it had a conical shape, but the ones you constructed in your book have upright primaries. What is the difference?
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wrote ...
I'm assuming that people make drsstc's have low secondary coil frequencies, like in the 40 or 50KHz range, because it lessens the stress on the igbt's.
Yes, thats always a goal. Personally, i always aim for about 200kHz max with the 40N60 type IGBTs, and aim for 50kHz for the CM600 types IGBTs. I'm sure they can be pushed farther, but thats what i design to.
wrote ...
Decreasing the pulsewidth would also allow to igbt's to switch less.
Yes, but you also reduce performance. Basically during operation, you want to increase pulsewidth just until you reach maximum length and do not go greater than that.
wrote ...
I was curious about the optimal shape of a primary for a drsstc. I have heard that a flat spiral is not the best, but what about a conical vs. an upright. I have seen one of Steve Wards Coils (the one that plays super mario brothers on you tube) and it had a conical shape, but the ones you constructed in your book have upright primaries. What is the difference?
Depends on your tastes as well as particular DRSSTC coil. Typically, the solenoid shape is used due to ease of use (to make) and tight coupling. Flat pancakes typically aren't used because they don't provide high enough coupling. The conical gives you high coupling, but with the added benefit that you have more voltage stand-off between top windings and secondary. But the conical is more difficult to make. Basically just comes down to personal tastes. I use solenoids on all my coils including some of the big CM600 based coils i have.
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DRSSTC Questions
