phase_accurate said:
But when I applied my new technique to this amp , the failure was gone....😉
You would hope so since you now have a constant voltage supply 🙂
From your description it seems like the bootstrap cap was never fully charging (as Charles stated) or you had a high amount of leakage current causing it to discharge too quickly.
From your description it seems like the bootstrap cap was never fully charging (as Charles stated) or you had a high amount of leakage current causing it to discharge too quickly.
BWRX said:
Could you more ellaborate on leakage current.....phenomena
But now it became much more robust with stiffened constant voltage source😉
There's certainly some leakage current due to stray capacitance but it shouldn't be much if the layout was good. The other possibility could be the driver chip itself, as Charles mentioned.
Hi Workhorse,
Happy to see that someone had the same problem i encountered with IR2113...
I tried different values for bootstrap capacitors and in hard clipping conditions output stage blew up...I think it was because of the bootstrap capacitor not charging enough to make the upper fet stay in saturation...
Can you tell more about your design ?
values you tried, fets you use...
Thanks
Happy to see that someone had the same problem i encountered with IR2113...
I tried different values for bootstrap capacitors and in hard clipping conditions output stage blew up...I think it was because of the bootstrap capacitor not charging enough to make the upper fet stay in saturation...
Can you tell more about your design ?
values you tried, fets you use...
Thanks
You shouldn't be happy that he was having problems 😉alexclaire said:
Were you using the recommended application circuit where the bootstrap cap is charged by a Vcc of about 15V?
If so, why don't you guys try charging the bootstrap cap from the positive supply rail with a series resistor. Place a zener in parallel with the cap to set what voltage you want it to charge up to.
alexclaire said:
The EF BJT is MJE340, Diodes are UF4007, Zener is 16V 1W type, and the resistor, thats the home work for you, as its rating is dependant on rail voltage and idle current as well...
I have used IRFP250/260/360/460, APT20M18LVR, APT30M35BVR etc.....and some IXYS stuff also...
BWRX said:
Thats known as PRE-Charging, but it doesnot help during Prolonged clipping events as the output gets strucks to the upper rail and then there is negligible current flow from that resistor to the cap....
But here in my technique, even when the voltage at output is struck to rail, the gate to source pulse voltage amplitude is still 15V constant, no matter how long its time interval is...Thats the figure of Merit for my technique....
Kanwar
Workhorse said:
If the capacitor can keep the FET fully on during the prolonged clipping event then it will help. Using the positive rail will allow you to fully charge the cap up to a higher voltage so that it will keep the FET fully on for a longer period of time. How much voltage can be used depends on what the chip and FET can handle.
Using a separate constant voltage supply will of course work under any conditions. The trade off is just added complexity.
odnaizutra said:
1.It saves PCB area and helps in minimizing parasitics
2.It has very much less component count [6 components] than NE555 charge pump type approach has
3.It is very very simple and much better
4.It is much robust and concrete solution
BWRX said:
A handful of 6 components is an Added complexity
A handful of 6 components which guarantee your amp would be safe in delivering DC, any type of Clipping output without any type of abnormal behaviour is an added complexity....
A handful of 6 components which could safeguard your FETs and Gate Driver Chip is an added complexity...
Just a handful of 6 components!
BWRX said:
so we can use it as floating voltage supply for hi side driver, and there is no need in 6 extra components 😀
I don't see much of an advantage doing this.
As already mentioned this wouldn't be much of an issue for a finished industrial product.
If one is selling modules then he better generates all auxiliary voltages on board since ease of use is always a good selling point. Lars Clausen's earlier modules needed an auxiliary voltage that he now "generates" on board -and I don't think that sales dropped when he made that decision.
As already mentioned you can also supply this current by a current-source from an auxiliary rail. It is not much current that is needed - less than 500 uA. For an amp with +- 100 Volt rails this would mean an incrase in losses of less than 50 Milliwatts. Not that much for an amp that could supply 600 Watts approx into 8 Ohms. The advantage of the current-source method would be less parasitic capacitance than any other method.
Regards
Charles
IMO, useless handful
1) i don't remember if 22-47uF of bootstrap, would be not enough for any realistic Qg and audio content (20hz 100% clipping even). DC = emergency, and amp must be shutdown instantly.
2) ir2110 already have under voltage protection (UVP<8V) for both outputs, to preventing poor Rds_on.
1) i don't remember if 22-47uF of bootstrap, would be not enough for any realistic Qg and audio content (20hz 100% clipping even). DC = emergency, and amp must be shutdown instantly.
2) ir2110 already have under voltage protection (UVP<8V) for both outputs, to preventing poor Rds_on.
phase_accurate said:
But if current demand exceeds, there must be excess voltage drop accross the cap...isn't it[provided very large Qg of Mosfets]
I think voltage source will help in maintaining the voltage level...much easily....
regards,
Kanwar
IVX said:
If it was that much reliable than reputed manufacturers like Crown, Powersoft, Ecler wouldnot use a "dedicated" floating high side supply rather than a simple bootstrap cap in their class-d amps....If they follow your type of opinion, then its Kaboom!
Actually 2.2uF is far enough if things are done in a clever way.
It's just a matter of adding some logic to force the high side to be turned off for, say 1us, if it has been on for the last 100us or so...
The low side capacitor has to be substantially bigger, though, say 22uF, to avoid draining it too much during the charging pulses.
Actually, the under-voltage lockout does a great job and the real problem is usually the low side capacitor being temporarily drained too much and causing other circuits to malfunction. If the high side capacitor is 220uF charged to 7V (UVLO threshold) and the low side capacitor is 22uF charged to 15V, the low side capacitor will be discharge to 7V almost immediately after the UVLO is triggered... This leads to a funny situation if more stuff is being powered with those 15V...
The too low UVLO thesholds of those chips may be a problem too, because Rds-on becomes too high before UVLO is triggered. However, the "watchdog timer" logic solves the problem.
It's just a matter of adding some logic to force the high side to be turned off for, say 1us, if it has been on for the last 100us or so...
The low side capacitor has to be substantially bigger, though, say 22uF, to avoid draining it too much during the charging pulses.
Actually, the under-voltage lockout does a great job and the real problem is usually the low side capacitor being temporarily drained too much and causing other circuits to malfunction. If the high side capacitor is 220uF charged to 7V (UVLO threshold) and the low side capacitor is 22uF charged to 15V, the low side capacitor will be discharge to 7V almost immediately after the UVLO is triggered... This leads to a funny situation if more stuff is being powered with those 15V...
The too low UVLO thesholds of those chips may be a problem too, because Rds-on becomes too high before UVLO is triggered. However, the "watchdog timer" logic solves the problem.
Eva said:
My earlier setup has 47uF for Bootstrap and 470uF for low side cap, but upon severe 6 to 11dB overdrive conditions it got smoked...but with my new technique it never smoked up again...mine is a low cost yet robust and reliable way to completely eliminate the problem.
Kanwar
Why not just add a voltage source to a source of upper mosfet i.e. parallel to normal bootstrap cap?
Why not just add a voltage source to a source of upper mosfet i.e. parallel to normal bootstrap cap?
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