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12v to 450v+ Boost Converter

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rupidust

Tue May 02 2006, 01:06AM

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Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
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Posts: 85

I like how you modded the voltage divider to be near the regulators voltage so that the reference on the non-inverter input would not require extra resistors.

Commanderbob

Thu Feb 21 2008, 05:18AM

Registered Member #1341 Joined: Thu Feb 21 2008, 05:06AM
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Very nice circuit. I am new to boost converters and this has helped ma a lot.

I have built a coilgun that has 8 330uf 400v capacitors. I am currently using an inverter that I bought from Digikey that is for florescent lights (I think), sadly it takes 8 min. to charge the caps (it is 1200v at 5ma). I have only one problem with this design. I have my capacitors arranged so the bank is 660uf 800v, 4P2S. Is it easy to change your schematic to double the voltage or should I just make all the caps parallel? With 800v I did notice a huge increase in power from the gun.

Edit: I was looking at the schematic more and what is charge switch for in the top right corner? Why do you need that if you have a power switch?

Thanks a lot,
Justin

uzzors2k

Thu Feb 21 2008, 08:29AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

If your coil gun was more efficient at 800V use that. To allow for more voltage from the boost converter you just need to use a higher voltage diode and mosfet/IGBT. The charge switch allows you to keep the charger on while not charging, basically put it in standby.

Commanderbob

Fri Feb 22 2008, 02:13AM

Registered Member #1341 Joined: Thu Feb 21 2008, 05:06AM
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I have a 1000V 50A IGBT and 1000V 1A diode, all I have to do is use these instead? I don't need to change the 555 at all? Also what is the highest voltage you can get with the regulator, assuming that all the HV parts are rated high enough.

Thanks for all the help,
Justin

uzzors2k

Fri Feb 22 2008, 07:25AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I don't think 1A is enough try at least 6A instead to be safe. The diode and IGBT current will depend on the peak inductor current, but that will again depend on inductance and frequency. The way the boost converter works here is constant power, so it will continuously pump energy into the capacitor, which in turn increases the capacitor voltage. So if left running it would charge the capacitor up to your diode/switch voltage rating. The 555 section can be left as is. The voltage sensor is set to 470V max the schematic says, you can easily adjust it by changing the resistor values in the divider.

Commanderbob

Sun Feb 24 2008, 02:07AM

Registered Member #1341 Joined: Thu Feb 21 2008, 05:06AM
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Thanks a lot. I am going to order the parts today. I have never used a 555 timer but they seem very useful.
Justin

Hazmatt_(The Underdog)

Sun Feb 24 2008, 02:22AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
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You know what would be a cool next step is to put a load sensing resistor in your supply and use that to modulate your pulse width on pin 5, so you have a tracking regulator.

Commanderbob

Sun Feb 24 2008, 02:50AM

Registered Member #1341 Joined: Thu Feb 21 2008, 05:06AM
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I want to power the circuit with +5v and not +24v. The part in the schematic is an IGBT. All the IGBT I found took more then 5v to turn them on fully. Could a MOSFET take its place?

How about

One more thing. What resistance should the inductor have? Does it matter? What about how much power it can handle?

Thanks,
Justin

uzzors2k

Sun Feb 24 2008, 07:41AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Yes a MOSFET could be used, but not the one you found. It will need to be designed for running from logic circuits, and have a threshold of about 1-2V. When the datasheets state on-state-resistance they'll specify what gate voltage was used, this will be the gate voltage needed for minimal on resistance. The BUZ31L can run from 5V, but it's only rated for 200V. Running your charger from 5V won't get you much power, you should use at least 12V, especially if you're charging to 800V.

Commanderbob

Mon Feb 25 2008, 05:13AM

Registered Member #1341 Joined: Thu Feb 21 2008, 05:06AM
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Posts: 17

Ok, but the G-E Threshold Voltage needs to be below 5v too right? This

IGBT says saturation voltage is 2.5 but the G-E is 5v 7v max. Would this work? I have a bunch of these for my coilgun. For the circuit to work at 5v both would have to be under correct?

Edit:This is for a robot that has a 7.2 Ni-MH battery.

Thanks,
Justin

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