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Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
Hi. I am looking for a working QCW modulator... There are hardly any QCW circuits on the net. I found this one: Will it work? If not - does anybody have a working circuit for me?
Registered Member #2922
Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226
You can use my phase-shift modulator. It can do all the modulation with not two stages, like the voltage controlled QCW. You can replace the uC with a complete analog control. This driver has a local oscilator to start the cycle, OCD, phase-lead.
Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
Hi Gregory. Thanks for the reply but i am only looking for the modulator/ramp generator. It should be simple to build... So does this circuit work properly?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Any simple analog ramp generator will work just fine, although a uProc will be easier to implement.
Basically you just need a steady-state bias level and a ramp. Both can be fed into a summing op-amp circuit and create the resulting waveform you need to feed into your buck or whatever circuit. For my own experiments, I usually set the steady-state bias for about 50-100V and then the ramp from that level up to the max.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
RateReducer wrote ...
I already found a circuit for generating the ramp but i am not shure which buck converter i shuld use...?
A buck converter is a buck converter. Its a specific switching power topology that is non-isolated and regulates to a voltage less than the input.
In the most simplistic terms possible, you would simply rectify your AC line through a doubler (i.e. 340VDC from 120VAC input), and then feed into a buck converter which would be modulated via that QCW ramp function where the output voltage would be the rail on your bridge feeding your coil.
So you would need to design a buck capable of those voltages, heat dissipation, as well as the proper bandwidth required for your specific application. (i.e. must be respond fast enough to your ramp function)
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
You can either implement a synchronous buck converter (using a half-bridge) or a single switch buck (much more common, bottom "switch" turns into a diode only). With IGBTs, there is no efficiency gain really for the synchronous buck. Normally its advantage is that it replaces a diode drop with a mosfet's low on resistance for conduction, but that only works with fets, as IGBTs are just as lossy as diodes for the most part.
The reason i used a synchronous buck to start with was because i thought it was necessary to be able to turn the output down without relying on the load to discharge the output. Later, i used a single switch buck so that there was no concern of cross-conduction between my 2 switches.
Sorry, no schematic from me, all my old documentation of that stuff is quite a mess.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
EasternVoltageResearch wrote ...
A buck converter is a buck converter. Its a specific switching power topology that is non-isolated and regulates to a voltage less than the input.
In the most simplistic terms possible, you would simply rectify your AC line through a doubler (i.e. 340VDC from 120VAC input), and then feed into a buck converter which would be modulated via that QCW ramp function where the output voltage would be the rail on your bridge feeding your coil.
So you would need to design a buck capable of those voltages, heat dissipation, as well as the proper bandwidth required for your specific application. (i.e. must be respond fast enough to your ramp function)
Sorry guys, just a Q, @ EVR, by proper bandwidth you mean the switching frequency of the Ramp (internal) to be compared on the resulting error waveform of the feedback and the output of the "ramp generator"?
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Looking for a QCW modulator
