Float or H-Bridge??? - Page 1
Forum section: electronics / projects

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 07, 2013, 04:22:29 am
content: Hey I was wondering which design I should use, its for a varible power supply rated for at least 20 Amps out @ 12V.Please I need some help with it and the pros and cons each design has. Also with the H-Bridge should i use two seperate driver circuits or can i use the same and invert them?

author: Kremmen
author_rank: Super Contributor
timestamp: October 07, 2013, 07:55:15 am
content: I don't want to rain on your parade, but i do wonder if you have a realistic/accurate picture of what you are taking on? For the reason that you ask this kind of question, i suspect your experience in implementing SMPS circuits is, shall we say less than master level. So a fair warning that what you are now attempting is not where you enter, it is where you graduate to. Sorry if i misinterpret your skill level.But to answer your question. Both circuits are possible with differing pros and cons. The pros of the resonant converter is the possibility for zero voltqage or zero current switching, greatly reducing strain on the switches. The con side is that your conversion frequency ius basically fixed to that define by your tank circuit. The nonresonant alternative is simpler and has no frequency constraints as such, while of course forced to do hard-switching, i.e. the switches operate under full voltage and current. In that sense it is not a question of what you _should_ use, more a question of what works for you.By the way, the more usual way to draw the resonant converter is to make it a H-bridge with the cap in series with the transformer primary. Your topology is a bit different and while it will most likely work, i cannot directly compare that to the "regular" resonant circuit off the top of my head.

author: ee.jmlp
author_rank: Contributor
timestamp: October 07, 2013, 09:46:16 am
content: (single phase)There are lots of ic's for h bridge applications.You can control 4 switches with 2 sources, one for the bridge and other for the control ic. Sometimes they use bootstrapping to control the high sides so you don't need 3 independent control sources plus the power source for a H bridge.Search in Newark for example: h bridge.But if you need to separate all switches to allow different configurations, you'll need 5 sources: 1 bridge power source + 4 control sources. That configuration gives you total control, you'll need fast optocouplers and strong drivers for each switch if you need fast switching speeds.(general)I use optocouplers like:http://www.newark.com/avago-technologies/hcpl-090j/digital-isolator-logic-gate-2500vrms/dp/82C4842They are really fast and expensive.If you start, you can try these (single) drivers from Microchip TC4452 (or TC4451 inverting), Micrel makes them cheaper (MIC4452) but they do not show the same performance. TC4452 are in my opinion, monsters (12A peak). Of course you can find weaker drivers in the TC series for smaller switches.(three phase)I saw you need a three phase, there are drivers for three phase bridges too. And something nobody will tell you, if you make long control wires (from the driver to the gate of each transistor) twist the gate with the source wire (N-mosfets) or use coax. and install a 16V low capacitance zener (15V control source) between the Gate and the source, as near of the switch as you can, that could save you lots of money.A bi directional zener (or two zener in anti-series) should help for faster turn off and reducing the capacitance.

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 07, 2013, 10:57:58 am
content: Thank you, you hit the nail right on the head for me, I want to be able to change the frequency of the output and that's why I asked. I have a few parts leftover from my amp build (NTE 58's) and was going to build a little test circuit. I drew it that way I did because its a basic bridged amp circuit.Check out my amp at:1000wattampproject.blogspot.ca

author: Experimentonomen
author_rank: Regular Contributor
timestamp: October 07, 2013, 11:18:28 am
content: These transistors are useless for switching converters. Only mosfets or igbts will work.

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 07, 2013, 11:51:02 am
content: The turn on switching time is to long for the transistor, or would they run to hot?

author: Experimentonomen
author_rank: Regular Contributor
timestamp: October 07, 2013, 12:27:00 pm
content: Way too slow, made for class ab(linear) audio amplifiers, not for switching.

author: ee.jmlp
author_rank: Contributor
timestamp: October 07, 2013, 12:36:47 pm
content: Look this mosfet: ipw60r041c6. I use them in 170kHz 300V 20A H-bridge configuration, they're fast, good and cheap.I saw 7 series from infineon IPZ65R019C7, it's even better but higher gate charge with faster parasitic inverse diode. If efficiency is not a problem you always can cancel the parasitic diode with schottky's and SiC diodes.

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 07, 2013, 03:35:59 pm
content: Thank you guys for all your input. I'll parallel fets on a heatsink, I'm sure I have some kicking around for testing purposes.... Is the cap in series with the load important for the inductive load?

author: ee.jmlp
author_rank: Contributor
timestamp: October 07, 2013, 06:56:45 pm
content: Capacitor is important when you do not control the bridge supply, when the parasitic diodes of the switches are slow or when you can't ensure a short-circuit-free load.

author: Experimentonomen
author_rank: Regular Contributor
timestamp: October 07, 2013, 10:28:28 pm
content: Resonant converters also offer less EMI than the hard switched counterpart as the current is more of a sinusoidal shape without sharp edges that causes ringing in the stray inductance of the pcb traces.

author: ee.jmlp
author_rank: Contributor
timestamp: October 07, 2013, 11:34:21 pm
content: I'd really like to see a zczv variable power supply made from scratch. Thunbs upEasy way is a shunt resistor for ZC and voltage divider for ZV, then use an IC to control the switches (psoc, atmel, etc..)Other would be similar but with a hall sensor or magnetoresistive devices instead of the shunt resistor for zc.

author: Experimentonomen
author_rank: Regular Contributor
timestamp: October 08, 2013, 09:24:58 am
content: As far as i know you can only have ZC or ZV, not both at once. Unless you pulse the resonant circuit, wait for it to ring down to zero and then pulse it again.

author: ee.jmlp
author_rank: Contributor
timestamp: October 08, 2013, 06:36:42 pm
content: Half bridge wil cost you less. I think is a good choice for 200W and it's easier to run it in resonant mode.There are controllers for synchronous rectifiers, TI has a bunch of them.

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 09, 2013, 01:24:20 am
content: In theory, I could run this at 10hz and vary it to 20khz right...

author: Experimentonomen
author_rank: Regular Contributor
timestamp: October 09, 2013, 07:41:29 am
content: You dont wanna use a that low switching frequency as it will be audible, also the transfomer would be almost as big as for a linear psu at that freq.Lowest freq i ever seen in a smps have been between 20-50kHz, most smps run between 50kHz to a few MHz dcepending on size and application.

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 09, 2013, 11:01:27 am
content: Well you see I haven't been totally true with my plans, I don't know if this makes any sence to ee but I'm always bugging around with frequency, so why not create a good high amperage high voltage (120Vac) frequency generator. (Since I live in canada 120 is line voltage I can use this as a variac). The only thing is that I want to isolate the output of the transistors/mosfets using a transformer (variac effect). If I ever want dc on the output, the circuit will simply run as high as it can and rectifiers will be used on the output. I know this will be heavy and frankly, I don't care...

author: GamerAndds
author_rank: Regular Contributor
timestamp: October 09, 2013, 01:36:46 pm
content: Thanks I would still need the h bridge to drive that into the transformer and a freq gen to drive it with sin sawtooth square or triangle. XD