IR2153 Half Bridge Mosfet Burning Problem - Page 1
Forum section: electronics / projects

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 11:25:23 am
content: Hello,I'm trying to make a half bridge converter based on the self oscillated chip IR2153 with an input of 220VAC and output of 12VDC. Before connecting to 220VAC, I've powered it with 24VDC bench power supply and measured the gate pulses. Those are very nice and clean. I've then connected it to 220V and checked the pulses again, still OK. But within a few moment, MOSFETs are burning randomly, and sometimes the chip also. There is no special situations when FETs are burning, sometimes with heavy load, sometimes with light load, and sometimes without any load. Sometimes both mosfets burns, sometimes only the high side one.I've used 12N60 and 7N80, all failed. Last two days I've damaged total 9 FETs and 5 chips.I'm working with the following diagram. Here you can see, there is only the gate series resistor. I've also tried with the gate-source pull-down resistor and gate to chip reverse diode. Nothing works.What's wrong with my circuit? How to save those FETs? Please help.Thanks in advance.

author: Andy Watson
author_rank: Super Contributor
timestamp: February 07, 2019, 12:21:10 pm
content: The upper FET has its drain in the wrong place. Whenever it turns-on it is shorting its own power supply.

author: wraper
author_rank: Unknown
timestamp: February 07, 2019, 12:38:01 pm
content: In addition to said above, it doesn't need voltage divider. 220uF cap connected incorrectly,and the shouldn't be 50k resistor. This circuit is a one big mistake.

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 12:50:29 pm
content: I'm sorry. Didn't noticed the error in diagram. But the actual circuit is OK, like this one I think.

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 12:58:30 pm
content: Quote from: wraper on February 07, 2019, 12:38:01 pmIn actual circuit, capacitor is in the right place, didn't noticed the error in the schematic.Whats wrong with the voltage divider?

author: Yansi
author_rank: Super Contributor
timestamp: February 07, 2019, 01:00:24 pm
content: Post a photo of the real circuit or pcb layout. That will tell a lot more.High voltage halfbridge driver chips with bootstrap like this are very sensitive about the pin 6 (output VS) becoming negative to ground. This negative voltage can occur due to wrong circuit physical layout.Also, change the piece'o'shit FR107 diode to something more appropriate like UF4007. FR107 is quite slow, when talking mosfet switching speeds. (Probably not cause of the burns, but definitely cause of other concern).

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 01:17:23 pm
content: PCB, currently I'm working onCircuit:Circuit: Copper side:At first I made my own pcb with an split supply and overload protection. But after some failure, I decided to work on a workable pcb, then gradually modify according to my need. So, I chose this pcb from an youtube channel where the youtuber shows it is working great. But I failed this time also, Burned 4 MOSFET in this circuit.

author: wraper
author_rank: Unknown
timestamp: February 07, 2019, 01:33:10 pm
content: Quote from: sbdada on February 07, 2019, 12:58:30 pmWaste of parts. If you already have cap in series with a coil, you don't need divider.And you still did not remove 50k resistor.

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 01:41:08 pm
content: "If you already have cap in series with a coil, you don't need divider."SO, how half bridge looks like without that? I've no idea about it. Can you please guide me?The 50K resistor is for biasing the chip. There's a 15.6V zener diode inside the chip.

author: Yansi
author_rank: Super Contributor
timestamp: February 07, 2019, 01:48:06 pm
content: The layout does not look that bad, but it is quite bad.Your GND of the control circuit is shared with a power ground. That is a big no no. Separate those two and join them exactly at the source terminal of the lower mosfet.Also, the whole control circuit resides directly inside the high current switching loop.I see you copied probably from PC ATX supplies, nothing wrong with that, except PC supplies used NPN transistor, which are rather slow switches, unlike mosfets. The decoupling capacitors must be in close proximity of the mosfets. And if they can't, separate decoupling foil type capacitor has to be used directly across the mosfet pair. (something in the ballpark of 1uF 630V here)Not sure why wraper is hating your bias resistor - some is needed for sure, to start operation of the converter. There is no way around it with this simple IC.//EDIT: Also, if you do not need dual input voltage range, there is no point in using two of those electrolytic caps in series. Use only one rated at 400V and tie the other end of the transformer to a capacitive divider. With just one cap, the design is cheaper (in case you need to buy those large caps) and the loop inductance and ESR is lower.

author: wraper
author_rank: Unknown
timestamp: February 07, 2019, 01:52:04 pm
content: Quote from: sbdada on February 07, 2019, 01:41:08 pmOpen the datasheet, first page.QuoteOK when I looked in the datasheet briefly, I got it wrong.

author: Yansi
author_rank: Super Contributor
timestamp: February 07, 2019, 01:58:03 pm
content: Also, I see one other major fail in the schematic: Your output filtering choke is wired wrong, and even on the PCB it seems it is!This way, the inductance is zero, because you pass current through the core twice, but in different directions each time.There is no point in having a dual choke like this. Let the out ground be only ground, and use only a single winding in series with the diode rectified output.The absence of any softstart in this circuit combined with the incorrectly wired inductor /no output inductance this way/ may cause to blow your mosfets.Add to that there is absolutely none over-current protection, the mosfet start will full turn-on cycle into empty output capacitors (short circuit in fact), while there is none inductance in series with them* to slow down the rate of current rise, ends them bad.* (other than the leakage inductance of both the transformer and the output choke)

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 02:00:51 pm
content: Hello Yansi, I didn't design this pcb. I got it from here:My own pcb was this:After burning some FETs here, I wanted to start from a workable circuit, so I chose that one. But still no improvement.

author: wraper
author_rank: Unknown
timestamp: February 07, 2019, 02:05:14 pm
content: QuoteIt's simply unsafe. Not enough distance between primary and secondary.

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 02:14:25 pm
content: Quote from: wraperIt's just a trial board, rough design. I was trying to find the faults and their solutions. Final board will be nice and clean, only if it works at all .Quote from: YansiFETs never blew on startup, everytime i connected load after powering up. And the maximum load was around 100 watts.

author: sbdada
author_rank: Contributor
timestamp: February 07, 2019, 02:30:59 pm
content: I've lost all my chips today. This chip is pretty rear in my country, and in my local market- they even don't know what is a gate driver. So, until I get new chips, i'm thinking to do some test with transformer coupled driver circuit. I've found this circuit on internet.I'm planning to drive the transformer with SG3525 or TL494.What do you think about this circuit?

author: TurboTom
author_rank: Super Contributor
timestamp: February 07, 2019, 09:38:39 pm
content: The clearance between the mosfet pins looks marginal. Better have the pads further apart and bend the transistor's pins accordingly, or stagger them. With the amount of flux between the pads as shown in your photo, creepage from drain to gate is a real possibility that will ruin the transistor instantly. Moreover, a ferrite bead on the source terminal may help reducing the very fast edges and ringing, also ultra-fast rectifiers anti-parallel to the drain-source direction of each mosfet may be beneficial. And you may possibly use an NTC in-line with the A/C input to slow down the startup a little.

author: jmelson
author_rank: Super Contributor
timestamp: February 07, 2019, 11:30:43 pm
content: Quote from: sbdada on February 07, 2019, 12:50:29 pmI make some PWM servo amps that have similar half-bridge stages, and use IR gate drivers in them. One of the things I found out was that the inductance of the load causes currents to flow that the driver cannot handle. So, here's the scenario : The high-side transistor is on, sending current out from the midpoint of the two transistors to the inductive load. Then, the high-side transistor is shut off, but the low-side has not turned on, yet. Current is flowing out through the inductance, and without the low-side transistor on, the current ends up flowing out through pin VS of the driver. This current is way too large, and destroys the driver chip, in the process, turning both transistors on at the same time and blowing everything out.Now, you say, "what about the body diode?" Well, I did measurements, and the FET body diodes are glacially slow to turn on. I was able to capture something like -7 V across the body diode for several microseconds, without ANY SIGN of the body diode starting to turn on.How did I fix it? Well, first, I put in an RC snubber to slow down the voltage swing at the midpoint. I use something like 4700 pF C0G capacitor (C0G to get LOW ESR and therefore reduce self-heating) and a 10 Ohm resistor in series, to ground. Then, I use an ES1D diode, also to ground, to prevent the midpoint from going below -1 V or so. This totally solved the problem. Proper trace routing to minimize trace inductance is also very important.Jon

author: Yansi
author_rank: Super Contributor
timestamp: February 07, 2019, 11:35:52 pm
content: The distance of TO220 pads is fine here. Not ideal, but on a clean conformally coated board, is actually quite good. And it is the last thing I would go after here.Ditching the IR2153 is definitely a smart move. If you are designing a power supply, doing it properly from the beginning can help a lot.Transformer based gate driving is pretty good technique and very robust one too.Make sure you use a suitable high permeability ferrite core, wound tri-filar (three twisted wires at once), and use wires with proper amount of insulation strength. (bare enamel (magnet) wire is NOT enough). TEX-F wire would be the best option, however sourcing that is not easy and is quite expensive. Poor-man's solution to that is using just three PE insulated solid core wires, but I would rather go for teflon, to be a bit more chilled.Note also the driving transformer inductance needs to be calculated so that the transformer driver can cope with the magnetization current.When driving the transformer with an H bridge, as you have likely thought of in the image above, the Q1 and Q2 transistors are not really required. Correctly wound gate driving transformer will have negligible leakage inductance and will provide pretty hard turn of currents by itself.You can use either 494 or 3525, botch chips are fine. The 3525 has the advantage of totempole outputs, hence could drive the transformer directly (don't forget to add a schottky diode pair to each output leg and make sure the output currents are not exceeded!)3525 also can be easily interfaced with a current sense transformer, to provide very fast over-current turn-off.494 has the advantage of being more flexible and provides two error amps, which are more flexible to be used in more bizarre configurations, than the error amp in the SG3525 (which just sucks).494 could be also interface to a gate drive transformer, if two PNP transistors are added to complete a totem-pole output stages.

author: Yansi
author_rank: Super Contributor
timestamp: February 07, 2019, 11:39:39 pm
content: Quote from: jmelson on February 07, 2019, 11:30:43 pmI call bullshit on that.I am pretty sure the body diodes are prettyfastenough to turn on for any half-bridge application. You should be way more concerned with the Qrr of those diodes, when operating the halfbridge in hard-commutation (i.e. a synchronous buck converter).However your solution with the diode to the VS is a nice trick, that has to be used on boards where the layout sucks.Even a bog standard 1N4007 probably turns on way way faster then a couple of microseconds. You have just measured your pcb layout parasitics, that may stand behind those nonsensical voltages.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 08, 2019, 12:05:38 am
content: FYI, I've not observed any forward recovery voltage in power MOSFETs. Reverse recovery is notoriously poor (100s ns at useful voltages), but that doesn't matter on an inductive load.I've used MOSFETs in heavily inductive applications at 400kHz, and not just little things with current tech, but the crappy ones that were available in the late 2000s (IXYS PolarHV I believe they were), delivering up to 10kVA from four SOT-227s in an H-bridge. (This would be typical performance from 4 or 8 x TO-247 package parts with modern SuperJunction devices.) Tons of time for recovery to occur, especially at higher forward voltage drop.To the OP: transistors don't just die at random. Consider saving yourself some parts cost, and frustration, by measuring the current flow and voltage drop across them. If the current or voltage is spiking very high, that's probably something to look into.Tim

author: sbdada
author_rank: Contributor
timestamp: February 08, 2019, 11:05:26 am
content: Quote from: T3sl4co1lI've tried to measure the voltage across the FETs and successfully measured the lowered FET's Vds. Without any load, It was clean, but with a load of about 100-150, there's some ringing and the waveform looks something like this: (didn't save the scope image)Then I turned off the converter, and connected the scope probe to the upper FET, and when I've powered it up again, it pooped without any load. I don't have any current probe, so don't know what's going on with that. But measured the input current with a multi-meter and results was not that bad.Quote from: jmelsonYes, I thought the body diode is enough, but now i'm planing to add extra diode. I was also thought about the snubber, but as i mentioned earlier, I'm working on other people's board, as they omitted that, i've also did the same. Moreover, I don't know how the snubber should looks like for half bridge. Something like this?:Quote from: YansiLast night I've sketched a rough pcb layout for that driver, because I hate to work on Veroboard, now etching the board. I'm going for SG3525 because I've lots of them. I've some black toroidal core, slightly bigger than those found in CFL which I found in a local junk yard. Don't know if they are Ferrite or Powdered. Also have some tube like core found in USB data cable, will try with both.I'm also planning to power the driver with a separate DC supply and also with a low voltage AC at High side, something like 60-100VAC. So that I can test it with low voltage FET, I've tons of them, will inform the update here soon

author: Yansi
author_rank: Super Contributor
timestamp: February 08, 2019, 12:23:20 pm
content: Adding extra diode is nonsense. You just add extra capacitive load (plus Qrr, if applicable to the circuit operaration). It will help nothing.Fck snubbers. Make the layout correct first, so it does not have to be fixed with snubbers. The only one likely neeeded will be series-RC across transformer primary.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 08, 2019, 04:30:52 pm
content: Quote from: sbdada on February 08, 2019, 11:05:26 amSeems to suggest ringing, could be a drive issue. Or it's that the load is reactive and it's ringing when let go.QuoteNo load? The scope probe is grounded to the scope body and mains ground. It's a pretty heavy load!!You need a differential or isolated probe to do that!Tim

author: jmelson
author_rank: Super Contributor
timestamp: February 08, 2019, 11:02:23 pm
content: Quote from: Yansi on February 07, 2019, 11:39:39 pmWell, I MEASURED it! No question, at least on the particular FET I was using, it was INSANELY slow to turn on. The clear proof is that these drivers stopped BLOWING UP when I added the ultra-fast diode across the low-side transistor. I'm not too worried by the Qrr, first the low-side transistor will turn on first in almost all cases, and secondly, these are low Qrr diodes (that usually comes with fast turn-on/turn-off). The transistor output capacitance swamps the diode Qrr (in my case, 56 A FETs.)QuoteNO, this device had a 47 uH output filter inductor, and when that inductor was sending 20 A current out from the midpoint, and then you turn off the high-side transistor, you have to provide a path for the current to immediately be sourced to the inductor, without allowing the midpoint to go below the turn-on of the internal parasitic diodes in the gate driver IC. My PC board parasitics are VERY good, I doubt they could be reduced much more, especially on a 2-layer board. But, with a 47 uH inductor, you can't stop the current instantly.Jon

author: boB
author_rank: Frequent Contributor
timestamp: February 09, 2019, 12:11:38 am
content: Your hand-drawn waveform looks to me sorta/kinda like you might have some cross conduction.You might try fiddling with the gate drive... The 22 Ohm gate resistors may be OK for turn ON but I would add, in parallel to those, a lower value resistor (say, 5 or 10 Ohms?) in series with a fast diode (USD1 etc) with its cathode pointing towards the IR2153 to make the gates turn OFF faster.I also wonder about dead-time offered by the IR2153 ? Haven't looked at that particular part. And does this part just run at 50% duty cycle ?I don't see any feedback mechanism but the schematic is kind of fuzzy.BTW, have you tried replacing the transformer with a resistive load for measurement purposes ? You can slowly bring the load up with various R values and then measure the heat of the components too. Are the FETs heating up ? The IR2153 heating up ?Gate drive can play a very big part. Maybe the drive isn't going high enough to really turn on the FETs ? Maybe they aren't turning OFF all the way although your hand-drawn pic looks kinda like there is a Miller plateau in about the right spot.Good scope instrumentation is really necessary for things like this. At least one differential probe is usually required. Cheap and workable are these ~$142.00 MicSig probes on Ebay.Also, the IR and IRS drivers can be VERY sensitive to over-voltage. That's one reason I stopped using them years ago. But they should work OK as long as you really watch their Vcc. I would make sure it's well within spec and not spiking up. At least you are using a real PCB and not a kludge.

author: Yansi
author_rank: Super Contributor
timestamp: February 09, 2019, 11:41:26 am
content: Tojmelson:Secondary current at dead time (both transistor switched off) is not circulated through the primary side in a halfbridge, but only through the secondary side. The voltage across secondary at dead time is 0V.The diodes on the primary side take only the magnetizing current of the transformer, not full switch-on state current. (In fact, when the secondary is shorted by both secondary diodes turned on, the only current passing through the diodes is the demagnetizing current of the leakage inductance).What FETs have you used? Please be more specific, otherwise it is just empty talking.As also T3sl4co1l pointed out, typical reverse recovery of diodes in 500-600V medium power mosfets is a couple hundred nanoseconds. Forward recovery is likely dominated by the ESL of the package (single digit nanoseconds).QuoteI'm not too worried by the Qrr, first the low-side transistor will turn on first in almost all cases, and secondly, these are low Qrr diodes (that usually comes with fast turn-on/turn-off). The transistor output capacitance swamps the diode Qrr (in my case, 56 A FETs.)With bootstrapped driver probably yes, in other methods of gate drive, high side fet may turn on first. This or that, is completely irrelevant to whether power loss from Qrr is applied or not - that is dependent on the load behavior, not which mosfet turns on first.Transistor output capacitance won't swallow Qrr. That is a misapprehension.As a reference, take for example this: STW56N60DM2 (600V 56A mosfet, so we are at the same level as you are talking about):https://www.st.com/resource/en/datasheet/stw56n60dm2.pdftrr: 245ns, Qrr: 2.6uC @50A, 150°C, 60V (Note no forward recovery is specified - because there aint any!)Equivalent Coss capacitance is 325pF, which at the rated 480V stores just 160nC. An order magnitude less charge is stored there.And Qrr does not get swamped, it is ADDed to the Qoss charge, as the other mosfet needs to push through the Qrr and Qoss of the other msofet - in a hard switching application. (Deadtime controlled halfbridge has a rather soft turn on).By adding external diodes in parallel, you are just making that worse (increased parasitic capacitance and another Qrr added).toboB: 22ohm is plenty small for turn off. Making it even smaller will help nothing. IR2153 provides about 500ns of deadtime, which is plenty. Yes, it operates at full duty cycle the whole time. (It is just a mosfet driver for fluorescent lights).//EDIT: Typos.

author: sbdada
author_rank: Contributor
timestamp: February 11, 2019, 10:43:13 am
content: Ok, I'm back. Last days, I've trying with different configurations of gate driver transformer. As I'm completely new at this, I was connecting different types of parts in different configurations randomly, and also a bit blindly. Some returns a good wave shape on the output, some didn't. The DC-restorer circuit show's the best output. But all of them exhibits a common problem. They draws too much current from the chip (with or without the diode or zener at the output), I measured minimum of 110mA to maximum 400mA, the chip can't handle it.I'm using the gate driver transformer found in ATX with a new winding (1:1:1). During test, I've also connected two IRFB4410Z MOSFETs without other circuitry to mimic the gate-source capacitance on the output.Then I've modified the circuit from (following image) A to B: First used single zener instead the back to back, this draws more current than before, though the signal looks well. To reduce that I've added a 1K resistor in series. This fixes the current but also increases the raise and fall time. Next added a diode in parallel to the resistor, this fixes the rise time, then added the pnp transistor to fix the fall time. After doing all this, the signal looks surprisingly better than before. With the capacitor in the input, there's some small ringing just before the raise signal, so I omitted that.Here's the gate pulses:In figure 1: You can see the two gate pulses with around 47% duty cycleFigure 2: Gate pulses with 30% duty cycle. some bumpy noise appears just before the rising pulses. Don't know where it came from.Figure 3: Rise and Fall time of a pulse.I've then removed the two dummy FETs and connected it to the main circuit and again tested the signals again. Everything was as before, only the bumpy noises increases by amplitude, though it is still bellow 2V, see Figure: 4.Also found that, this noise appears only when the duty cycle is in between 12% to 40%.Also note that this noise was present whole time in those configurations I've tested before, and there the amplitude was too high. In worse case, it was about 6.5V.After doing all this test, I've powered up the main circuit with 110VAC. This is the wave shapes of lower FETFigure 5: Max duty Cycle (47%), without any load. Output: 6.85VFigure 6: Max duty cycle, A Nichrome heating element connected at output. Output: 5.38V, 4.64AFigure 7: 25% duty cycle, No Load. Output: 6.8V.Figure 8: 25% duty cycle, Same heater as load. Output: 3.16V, 2.84A.Notice the wave form of Vds with duty cycle decreased. This is my first Half-bridge converter, so I'm not familiar with that. I don't know if the signal is ok or not. If it is not ok, then what's going on here? What should be my steps to solve this?I'm not going to apply the full voltage (220VAC) before being 100% sure.This is the worst SMPS Circuit I've ever made, floating wires and components everywhere, look at the picture bellow, you'll understand. After all this test, not a single FET has blown up, I'm surprised.

author: sbdada
author_rank: Contributor
timestamp: February 11, 2019, 11:07:23 am
content: Quote from: boBI did that, but that didn't prevent them from blowing.Quote from: boBIR2153 has a duty cycle of 1.2 µs, and it has no duty cycle controlling system. With a feedback circuit, it just shut down the output when an over-voltage occurs. That schematic is an screen capture from youtube, that's why it looks fuzzy.Quote from: boBYes, I did that, but only upto 24-30 volt and the resistor was 330Ohm, so the results are not that useful I think.Quote from: boBIf the transformer driver works, I'm also not going those again. I had a bad experience with IR2110 and now with IR2153. My knowledge and skills are too low to handle them.Quote from: YansiWhat will be the value of R and C? My guess is the R's value will be less than the impedance of leakage inductance. Am I right?

author: Yansi
author_rank: Super Contributor
timestamp: February 11, 2019, 11:30:08 am
content: Jeezus crist (if you have one in Bangladesh)... instead of randomly slapping things together, why not do it correctly the first time? There is not much to building a couple hundred watt off-line converter. It is just about following some basic enginerding and good construction practice.Your extreme "random slaptogether something" approach is really not helpful. First, it is not correct way to do things, and second we can't keep up both with your changes in circuit and your mind.So, could you please tell us, what is your ultimate goal? Write up the specification of the power supply you are building, i.e. the mains input voltage range, the nominal output DC voltage and maximum load current. At least those, so we can start with something.I am willing (and others probably too) to spend the time helping you out, but we must start from the ground up. So what are the specs for the supply?and by the way, your modification of A to B is downright wrong. The 1k resistor does close to nothing and the zener diode (if only one used) short circuits the gate drive circuit, as the signal on the secondary has both positive and negative polarity!

author: sbdada
author_rank: Contributor
timestamp: February 11, 2019, 12:50:28 pm
content: Sorry if I confused you guys. Here are the specs:Input Voltage: 220VAC +-20VOutput Voltage: 12VDCMax Output Current: 8A

author: langwadt
author_rank: Super Contributor
timestamp: February 11, 2019, 12:55:36 pm
content: Quote from: sbdada on February 11, 2019, 12:50:28 pmhttps://www.robotdigg.com/product/547/12-or-24v-power-supply-for-stepper-motors

author: sbdada
author_rank: Contributor
timestamp: February 12, 2019, 08:07:53 am
content: Quote from: langwadtI don't want to buy, because I don't need it. I've lots of SMPS. Some I bought, some I made, they works well. But all are flyback. I am willing to make the half bridge so that I can understand it better.Thanks

author: Yansi
author_rank: Super Contributor
timestamp: February 12, 2019, 10:40:37 am
content: 12V 8A does not sound that problematic, should be pretty possible.Do you want to use mosfets on the primary side, or are you fine with having play with NPN switching transistor?I say that, because for the "kind of old" solution with NPN switches, the components are already very abundant on every scrap pile and it is quite easy for implementation. The typical off-the-shelf power supply boxes in the perforated metal cover are NPN transistor based mostly anyway (if they are not something rather expensive modern).Also, the NPN solution is neat with that the control circuitry and regulation is all on the secondary side, so it is easily worked with, also power supply voltage for starting operation is created by the primary side being self-oscillating.With MOSFETs, the matter with an halfbridge is different, as you would need either: Specialized ICs on the primary side, that can start operating right from the 300V DC bus, otherwise you end up with that heating element in the supply as you have had with the IR2153. Which completely nullifies the point of trying achieve better efficiency with MOSFET switches.If the control circuitry for the mosfets would be placed on the secondary, you likely end up having to add a separate auxiliary power supply, as the mosfet halfbridge can not start self-oscillation, as it nicely happens with the NPN halfbridge.The auxiliary power supply may not be problem if you just want to play and learn, but it may become forbiddingly expensive for a product to be manufactured in quantity - hence why the neat and well proven bipolar (NPN) transistor power supplies are still used today.To sum up, you need to first pick a choice from likely these three:1) NPN bipolar transistor half-bridge. (cheap, simple proven design, components easily available)2) MOSFET with primary side control circuitry (needs special ICs to handle the 300+V startup, not as easy for the regulation loops - galvanic isolatione)3) MOSFET with secondary side control (requires auxiliary power supply for the control circuitry to start up).Others please make a note if I have forgot something.As you obviously want to just have a play with it and learn, I would go down the 1 or 3 route, whichever you may find more interesting.Also note, that due to the bipolar transistor being rather slow switching devices, they are more tolerant to circuit and PCB layouts and also they cost much less, if you blow shit up - you just take another two from the scrap pile

author: sbdada
author_rank: Contributor
timestamp: February 13, 2019, 07:40:37 am
content: I don't know why, but I've a soft corner for MOSFET, specially for N-Channels. In every application, I first think about them, then the other switches, though I don't know or understand FET-s muchObviously I'm going for number 3. I'm not worried about the cost too much, because I'm not gonna manufacture or sell it, it's not my business.Currently I'm making a new pcb layout, trying to make it as clean as possible. Any suggestion for me?I'm adding an extra winding to the main transformer, which biases the control chip - 3525. Initially it'll be started with an external power supply, I hope this winding will able to feed the chip after start. Because it is only for test purpose, this type of startup or even full operation won't be any problem for me.A question, Did you see that figure: 8 of my previous reply? With lower duty cycle, does that Vds wave shape is correct?Thanks

author: PhongLap
author_rank: Newbie
timestamp: January 27, 2021, 02:07:22 am
content: Quote from: jmelson on February 07, 2019, 11:30:43 pmIs this your snub net-work? I'm wondering how this true look