High Side N-MOS Driver with High Speed for a big Project - Page 1
Forum section: electronics / projects

author: rentner
author_rank: Regular Contributor
timestamp: February 27, 2014, 10:01:40 pm
content: I need a high side driver for 350V potential difference. The duty cycle is as low as 5%. I need to use an N-Channel MOSFET, because equivalent P-Channel types are not available for me and would also be by far to expensive.The frequency is 200kHz and Duty Cycle is 5%There is a dead time involved, that is about 60ns at max. So the prefered max delay of the circuit is well under 30ns.The signal has a rise time of up to 25ns. The Amplitude is from a few millivolts to 12V at 10k load.The MOSFET I want to use is the IRF740 with a Gate charge of 43nC. (400V MOSFET)As well I will use 2 in parallel. The Circuit should consume less then 5W for each MOSFET. With careful design this should be possible.The price to each driver should be less than 5 bucks for a single Circuit of mine (it might as well be sold commercialy so the price might sink to as low as 2 bucks at max).I don't want to tell you yet, what this is for. If someone is able to help me with that and there is interest for other people and I come to a "mass" production (of a few dozen only) the one who made this work will get one of this "circuits" as a present. So nobody should have a problem in thinking "and what's the deal for me?". One unit will be worth at least 200 bucks. But I am working on this for over a year now testing out new stuff some days and always failing. As some on this forum might know: I only want discrete parts. That is my absolute passion.Also one thing: I would prefer SMD parts (for prototyping still hand solderable parts, meaning not as tiny as 0201 resistors.). Through hole still is ok!And now another possibility: If it does not come to a commercial product due to lack of interest, I will still present the one who helped me with something interesting and still at least 50 bucks worth. That is an absolute promise! I will count the first "perfect" solution only.So a small List of what I need:350V High Side Driver (preferably bootstrapped)-200kHz-Duty Cycle as low as 5%-delay well under 30ns, as symetrical for on and off as possible (so 20ns Delay on turn on should be 20ns Delay on turn off!)-rise and fall time less than 30ns-Input Signal is GND to 12V-Ultra Stable switching-Stability over dV/dt-caused-turn-on of Mosfet Gate (Means low resistance gate driving)-High Side Mosfet has up to 350V potential over GND!-MOSFET used: IRF740 (Gate charge: 43nC, 400V MOSFET)-DISCRETE! (Resistors, Capacitors, Transistors, Inductors, Diodes, 4 pin Opto Couplers)All parts must be available quite easy for Europe and should not be canceled the next 2 years.This project will be rised to Crowdfunding with the help of a friend.Thank You for help! You WILL not regret this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 27, 2014, 10:56:10 pm
content: Transformers aren't discrete..?What do you mean by,Quote from: rentner on February 27, 2014, 10:01:40 pmMillivolts as in, logic '0' has a value of millivolts?What current capacity does the signal source have?For that matter, how much load current is required, and what are the load characteristics? Is it resistive, inductive, capacitive, etc.? Can you provide an equivalent circuit? Is this driver and high-side switch part of a half or full bridge circuit?Note that 5% duty at 200kHz is a pulse only 250ns wide.What is the voltage supply? If it's AC line, 400V devices will be lucky to survive at best. 500 or 600V devices would be a better choice (IRF840... or newer, preferably).What mechanical constraints do you have? Single board, SMT? THT? Heatsinking: none, or how large can be tolerated? Operating temperature, humidity, dust in the environment?EMC (electromagnetic compatibility), if any? Risetimes like this will throw off lots of RF energy. Without careful design, the circuit can upset itself, resulting in poor pulse form, oscillation, control errors, etc. Let alone anything nearby. Filtering and shielding may be important.QuoteIncluding stocking and assembly costs (...depending on where in eastern Europe it's being manufactured..?), you'll have a hard time achieving that in such a small quantity. If you already consider this, and mean parts alone, then nevermind.All in all, you'll have a damned hard time beating an IR2110 or something like that, including import costs.Tim

author: rentner
author_rank: Regular Contributor
timestamp: February 28, 2014, 12:07:21 am
content: Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmI did consider that as an Inductor. Of course it is allowed, since there is no complex circuitry in one package (as long as we don't count the parasitics at least)Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmI mean the Signal changes between almost ground and almost 12V+. At least without extra load. This is an inverting output with a 1k Pulldown resistor. This gave me the best signal. And that realy needs to be one.GND Voltage is Logic '0' and 12V is Logic '1'Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmJust as mentioned above: 1k pull up and at least 3k pull down does give still clean signal.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmCurrent up to 20 Amps can flow!It is inductive. The inductance is about 100uH. It is like a step down converter but with only with 100uH. (which does not give all to much ripple current at all). It is (thanks god) only a half bridge. Let's (for simplicity) consider it as a half bridge Class D or Buck Converter stage.About the current: 20 Amps of course does not flow continously. And theoretically ther SHOULD be no peaks. But I cannot say this will work in real life, as long as I did not see this. The Inductive output also has Parasitic capacity.I chose 2x10A MOSFET since this is quite inexpensive and the IRF740 has a relative low gate Capacity which is important. Otherwhise the miller Capacity might kill it. Also a clean signal could be quite difficult... 250ns Pulses as you calculated are not the best for a 100nC MOSFET an higher. Please correct me, if I am wrong.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmThe Supply is actually 330V DC. I added 20V safety margin an 350V is still not high enought to kill a 400V MOSFET, I hope.Would you think, this MOSFE would die? I hope not... If so, the IRF840 looks good aswell. But that would require 3 High Side Drivers and 3 Mosfets. Quite a challenge, but that will be ok.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmThis High Power stage will propably be build as a single Board. Surface Mount topology is prefered. Some parts will be Through Hole, wherever it is required.The Ambient Temperature should be less than 60°C and higher than -10°C to maybe 0°C. Humidity of anything that is present in a house (except the kitchen). Dust should not be a problem. The whole unit will be cooled just a tiny ammount by a fan in the case. Any hole will be dust-blocked with a dust filter. There are no mechanical parts planned, that die from dust anyway.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmYou mean, if this product should meet local requirements? Of course, since it is something, that (hopefully) will get sold sometimes and should not be limited for some countries. The Board with the switching going on will be shielded in a full steel casing (1mm) and the whole product itself will be shilded with metal.The High voltage section will be made as tiny and with as short connections as possible to reduce this as good as I can. But clearance must be enought still. I am well aware of PCB working as an antenna. I will not loop anything with HF and High Current for sure.I hope, there will not be to high oscillations. I don't want to waste to much power for nothing Also dV/dt could kill the MOSFETs.I have to say, that I realy did not find anything better than IRF740, that is available so easy for me. Also it is cheap and good.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmI just mean the prototype should cost less than 5 bucks. And the mass version should cost less, since many components of one type are much cheaper. I did not count the shipping for that. I just meant the component costs. I mean, if it is not possible, to make it that cheap, I will propably accept, as long as it is not damn expensive.I know, that assembly will not be cheap at all. I still hope, I get this as cheap as possible.Quote from: T3sl4co1l on February 27, 2014, 10:56:10 pmYeah, I know. Discrete Components can be a hard game...I realy hope, I wrote everything! Puh, what a text.Working on that "in the background" for a year now. Never got it done. I must be missing something, but what?

author: rentner
author_rank: Regular Contributor
timestamp: March 03, 2014, 05:23:18 pm
content: How do commercial Products do this? Like the IRF2110 or similar. I mean, there must be a reason, why there NEVER is any internal circuitry diagram in the PDF.Just Imagine! For example MANY Class D Amplifiers work with a megahertz or even higher! How do they realize that incredible switching speed? I can hardly imagine that at all.How to build up a working High Side driver for N-Channel Fets? There is also one problem: The high switching speed could turn on the high side Mosfet again and shoot throught might appear. How to solve that issue aswell?

author: nctnico
author_rank: Super Contributor
timestamp: March 03, 2014, 09:11:36 pm
content: I second using the IRF drivers. There is one big issue though. They usually have a boost capacitor which gets charged when the low side is on. You need to take care of this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 04, 2014, 02:02:02 am
content: You're welcome to try making your own bootstrap HV driver, but if you get the common mode rejection wrong or whatever, you're pretty much screwed. I wouldn't trust one to more than a few times its supply voltage, nor around fast risetimes (say, above 30V or under 50ns). I don't have a problem trusting monolithic devices, because they already solved that problem.Tim

author: JimmyM
author_rank: Regular Contributor
timestamp: March 11, 2014, 12:59:12 am
content: I was just looking at an app note by IRF. AN-978. Lots of good approaches in there. Things get easier when you don't need to do continuous ON.Look into capacitively coupled gate drives. It may be as simple as a zener, resistor and a series capacitor between your PWM and the gate. You would need a 400V ceramic capacitor or similar low ESD device.