Switcher supplies?
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guest
Re: Switcher supplies?
Hi Guy, That sounds an impressive power supply, I'd be very interested in how it comes along, I'm a fan IGBT's as I'm of the opinion they are rugged enough for the job and not too hard to drive. Unfortunately (or fortunately) I've chickened out and gone for the low tech but reliable approach as I scored three suitable transformers for about $15 US total!! : they are 9.2 KVac 400 VA single phase transformers made by Westinghouse for their electrostatic precipitators, according to the control box they came out of they are rated at 13KV DC @ 30 mA continuous. They appear to be a lot more conservatively rated than the neon transformers as they are twice as big as similar VA rated neons so I'd be more inclined to believe the spec. These things are designed to run continous duty at full power so I'm hopeful of dragging a little bit more current out of them, they don't appear to be current limited like a neon tranny as the circuit had massive high value resistors in series with them for current limiting. In theory I should be able to get up to about 38KVdc and say 30-40mA current out of them.
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guest
Re: Switcher supplies?
I've often thought about doing just what you are doing.
What is the design output voltage? Amperage?
This doesn't sound too portable.... How heavy is it going to end up? Ive even thought about starting from 12v and using a bank of batterries in parrallel to get needed amperage. It sounds like a workable approach.. I'm getting tired of trying to spec off Ebay..
Might be cheaper to design exactly what you need rather than hunt forever on the net.
Larry Leins
Physics Teacher
What is the design output voltage? Amperage?
This doesn't sound too portable.... How heavy is it going to end up? Ive even thought about starting from 12v and using a bank of batterries in parrallel to get needed amperage. It sounds like a workable approach.. I'm getting tired of trying to spec off Ebay..
Might be cheaper to design exactly what you need rather than hunt forever on the net.
Larry Leins
Physics Teacher
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guest
Re: Switcher supplies?
Well, I am shooting for at least 40KV for the output. It should be able to pump out at least 30-50 ma at that voltage. It really depends on how efficient the HexFETs and my custom design output transformer end up. The HexFETs have a low Power-On impediance. but I am not exactly sure how much heat loss I will be generated by the HexFETs. I don't have any expensive modeling tools to find out, so I have to do it the old fashioned way, by trial and measurement. I am also concerned with the output HV diodes. They probably will not be able to operate at high frequencies. So I probably will need to drive the output transformer at a less than optiminal frequency. I am still searching for a decent set of HV diodes. There aren't too many manufacturers of HV diodes in the 60+ KV range that aren't for industrial use. Many of the manufacturers offer HV diodes in the 10-1000A range. I dare not think of how much those babies would cost! I am looking to avoid tube based recifiers because 1. I haven't done any work with tubes, and 2. I am also aware that running recifier tubes at HV produces lots of X-rays.
I am going to include variable voltage output by using a combination of changing the driver frequency and duty cycle, so I can run at different voltages for testing. I am also including two circuit breakers (one on the primary winding of the input transform, and another on the primary winding of the output transformer) to limited excessive current draw. Beware of the different types of circuit breakers. Avoid "thermal" breakers, since they will permit overcurrent operation to run for several minutes. You want to use "magnetic" breakers that trip within seconds.
FYI: You might want to consider using HexFETS instead of IGBTs. I investigated the using IGBTs for my design and choose HexFETS over IGBTs because the HexFETS have built in load balancing. The Rds or ON-resistance increases with the temperate of the device. so if you have multiple HexFets coupled together they will automatically distribute the load. HexFETS are very easy to drive and don't have latency problems of the IGBTs. If you look on International Rectifiers web site http://www.irf.com , they have several white papers on HexFETs, including how to drive them in parallel.
As far as the weight, I would expect the whole unit to be between 30-35 pounds. I plan to mount the power supply in a standard 19 inch equipment case. The weight isn't the problem, its cooling! I suspect that this power supply will have a dual use as a rack mountable space heater!
I am going to include variable voltage output by using a combination of changing the driver frequency and duty cycle, so I can run at different voltages for testing. I am also including two circuit breakers (one on the primary winding of the input transform, and another on the primary winding of the output transformer) to limited excessive current draw. Beware of the different types of circuit breakers. Avoid "thermal" breakers, since they will permit overcurrent operation to run for several minutes. You want to use "magnetic" breakers that trip within seconds.
FYI: You might want to consider using HexFETS instead of IGBTs. I investigated the using IGBTs for my design and choose HexFETS over IGBTs because the HexFETS have built in load balancing. The Rds or ON-resistance increases with the temperate of the device. so if you have multiple HexFets coupled together they will automatically distribute the load. HexFETS are very easy to drive and don't have latency problems of the IGBTs. If you look on International Rectifiers web site http://www.irf.com , they have several white papers on HexFETs, including how to drive them in parallel.
As far as the weight, I would expect the whole unit to be between 30-35 pounds. I plan to mount the power supply in a standard 19 inch equipment case. The weight isn't the problem, its cooling! I suspect that this power supply will have a dual use as a rack mountable space heater!
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guest
Re: Switcher supplies?
HEXAFETS get pretty toasty in high load conditions.
I built an inverter out of them and ended up using an old hairdrier with a bad element to blow high speed air on the semis... they can easily burn themselves into oblivion.
Pretty neat on the weight I must admit.
The x ray problem on tubes is fairly easy just put it in a steel box. Russian tubes are very cheap but they also have a high voltage diodes in the 500 - 1500 volts at 200 amps.
Line them up into a diode stack. I'm using diode stacks from x-ray machines good for 100 kv at 40 ma.
Larry Leins
Physics Teacher
I built an inverter out of them and ended up using an old hairdrier with a bad element to blow high speed air on the semis... they can easily burn themselves into oblivion.
Pretty neat on the weight I must admit.
The x ray problem on tubes is fairly easy just put it in a steel box. Russian tubes are very cheap but they also have a high voltage diodes in the 500 - 1500 volts at 200 amps.
Line them up into a diode stack. I'm using diode stacks from x-ray machines good for 100 kv at 40 ma.
Larry Leins
Physics Teacher
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guest
Re: Switcher supplies?
I am going to build special heat sinks for the HexFETs. I've purchased some High CFM 12V fans that I will attach to the heat sinks. The Heat sinks will be constructed out of copper since it's really good at heat transfer.
If I can't find any acceptable semiconductor HV diodes, I will look into using tubes. Do know of any good documents/URLs that cover tube recifiers?
If I can't find any acceptable semiconductor HV diodes, I will look into using tubes. Do know of any good documents/URLs that cover tube recifiers?