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Terry's DRSSTC - Phase Detection/Controller



Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

Here is the latest idea I am working on to detect the phase of the primary loop current to drive the IGBTS:

http://drsstc.com/Design/CurrentPhaseDetector.gif

It is pretty similar to the one in Dan's book but this one does hundreds of amps for the primary side current control.

CT1 is a center taped 100:1 Current Transformer. The center leg is taken as ground. D1 and D2 clamp the negative going signal and D3 and D4 clamp the positive against a 4.7 volt Zener power rail. The CT+ and CT- outputs get slammed against these rails pretty hard so the 4.7 volt Zener system is isolated from the +5V power supply. The +5 volts just charges the rail during power off. The output swings between -1 and +6 volts but that is ok in this case. I like the center tapped CT since the forward logic only has to play with positive signals now which saves a lot of trouble.

The main controller is still being worked on but it looks a lot like this

http://drsstc.com/Design/Controller.gif

The signals from the CTs got to two OR gates. One is null and the other (U1b) is used to inject the initial firing pulse. The rising edge of the PULSE signal fires a ~3.3uS pulse from U5a which turns the H-bridge on and gets things going. U2c "can" shut the thing down if some odd current is detected during the initial pulse but it is really just there because it looks good ;-)) U2a and U2b prevent both sides of the H-bridge from being on at the same time no mater what. U3a and U3b are the main AND gates that take all the signal and produce the logic drive signals. They also add the FAULT shutdown at this point. U4 is a QUAD balanced line driver chip that drives the LEDs on the TLP250s It puts out about 0.5 to 3.5 volts under load thus the seemingly small resistors. That helps since the smaller resistors can drive the LED junction capacitance better. The capacitors (C2-C5) give the LEDs a nice hard kick to help them turn on and off really fast. Since all the ICs are really fast, the propagation time through the whole mess is a little less than 40nS! The circuit does have plenty of hooks to play with timing and dead time if needed. It will be on a bread board at first so I can fiddle as needed with it once it is actually in circuit.

I have started working and the cabinet:

http://hot-streamer.com/temp/PC230007.JPG

Just mounted the power supply, capacitor drain/charge resistor, bridge rectifier, little power resistor, feet, and the rack handles. I'll add the line filter and connector blocks to the back next and then do the front panel last after I have had practice ;-) Most of the ordinary stuff will mount on the sides out of the way, leaving plenty of room for the cool stuff.

So that's where I am at. Most of the stuff at www.drsstc.com should be up to date now too.

Cheers,

	Terry