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LAN_403

HV Enthusiast

Tue Jun 27 2006, 11:43AM

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

Here is a simple generic interrupter (modulator) design which can be used for both SSTCs, DRSSTCs, and VTTCs. Based on standard 555 timer astable and monostable configurations, it features:

Adjustable Pulsewidth
Adjustable PRF (BPS)
Burst Mode (Adjustable Rate and Dwell times)
Single-shot mode with adjustable PW and lock-out debounce

The single-shot mode allows you to specify pulse duration (up to 5ms) in my example, and also includes a lock-out circuit to prevent retriggering which has its own adjustable delay.

The complete design will be added to my website in a few days, but here is the preliminary schematic, excel design sheet to customize your interrupter, a front panel design, and the box the front panel design was designed for. The box, made by Serpac (Model 17S), is available in black and white in EMI style enclosure. I'll also be adding artwork to my website for download which is designed to go with the $51.00 ExpressPCB order (3 boards)

Enjoy!

Schematic (Preliminary)
]1151408599_15_FT0_advanced_modulator01.pdf[/ file]

Design Sheet - EXCEL
]1151408599_15_FT0_interrupter.zip[/file]

ragnar

Tue Jun 27 2006, 11:50AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Aw, cute!

How high does can the PW/PRF circuit theoretically go, disregarding the 300hz setting?

HV Enthusiast

Tue Jun 27 2006, 01:13PM

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

will depend on whatever the limitation of the 555 chip is and what the system is capable of.

coaster_chris

Tue Jun 27 2006, 07:18PM

Registered Member #359 Joined: Sat Apr 01 2006, 09:27AM
Location: Utrecht, The Netherlands
Posts: 16

Nice work Dan! It looks very good!
Might be something for me if I will get my SSTC working some day...

Chris

Reaching

Wed Jun 28 2006, 10:27AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

mhh, nice work dan, from what i understand you can adjust the PW and PRF independend from each other, so for example 100ys stays the same regardless on what you set the Pw? exactly what i want, dont need the other modes though.

HV Enthusiast

Wed Jun 28 2006, 11:38AM

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

Reaching wrote ...

mhh, nice work dan, from what i understand you can adjust the PW and PRF independend from each other, so for example 100ys stays the same regardless on what you set the Pw? exactly what i want, dont need the other modes though.

Yes. The PRF 555 is the classic 555 astable single RC oscillator producing pulses at some rate. These pulses are your overall PRF. The negative edge of these pulses is then used to trigger the PW 555 and produce a pulse which is output to the DRSSTC. Both are independent of each other. Its not my design, but lifted right out of one of the app notes on the 555 timer. The burst adjust is merely another gating and works an as OR basicaly to the output of the PW 555 chip. This burst mode addition was borrowed from Steve Ward's intteruptor circuit he has on his website.

I originally had planned on using a PIC based interruptor design with lots of features and the first prototype worked very well, but it just took too long to make different adjustments and got to be a pain in the arse. So, i went completely analog using discrete components so adjustments could be made very quickly on the fly.

I'll be uploading artwork, etc... to my website soon.

Reaching

Wed Jun 28 2006, 08:02PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

nice circuit, i tried it out today and it works really fine, you can adjust the on and off times nearly independend from each other, that is great.. but Dan whats the use of this diode in the circuit (1n4002)?there is no difference with or without the diode in place

HV Enthusiast

Thu Jun 29 2006, 12:39AM

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

Reaching wrote ...

nice circuit, i tried it out today and it works really fine, you can adjust the on and off times nearly independend from each other, that is great.. but Dan whats the use of this diode in the circuit (1n4002)?there is no difference with or without the diode in place

Recall, that there is no DC connection between U2 and U3 timer circuits. Each circuit is AC coupled only through capacitor, C7. When U2 output is in steady state (non-switching), the trigger input to U3 is pulled up to +9V through R9. Regardless if the output of U2 is low or high, the trigger input to U3 is pulled high. The only thing that the trigger wants to see is a negative going pulse (to less than 1/3 Vcc). When the output of U2 goes from high to low, this negative pulse will go through capacitor, C7 and pull the trigger input low, thereby triggering U3. However, when the output of U2 goes from low to high, there is a tendency for the trigger input voltage (because it is now DC decoupled) to go above +9V. This is where the diode, CR3 comes in. It protects the trigger input from excessive voltages as when the trigger input exceeds about 9.7 volts, it will conduct through the diode to the rail, and thereby reduce spiking.

Steve Conner

Thu Jun 29 2006, 09:14AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I'll take this opportunity to pimp my DRSSTC interrupter too.

It allows the pulse width to be adjusted from 10 to 300us and the rep rate from 0 to 200Hz. The adjustments don't interact with each other, and turning the rep rate control to zero puts it into a single shot mode with lockout. It doesn't have burst mode like EVR's design, but it does have a linear adjustment law, so you can easily make scales for the knobs, or use 10-turn pots with counter dials. I'm working on adding the long pulse feature that Ward used to such effect.

It also features the scopeboy.com exclusive "Big Red Lighty Up Skull And Crossbones Fire Button".

HV Enthusiast

Thu Jun 29 2006, 10:42AM

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

wrote ...

I'm working on adding the long pulse feature that Ward used to such effect.

Your circuit should be able to do the long pulsewidth feature as is in one-shot mode.

Anyways, here is my final schematic. I ordered the wrong switches (DPST instead of DPDT), so i had to make a few modifications to work with my front panel set-up. Works great!

]1151577766_15_FT12187_advanced_modulator01.pdf[/ file]

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