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Old 26th March 2006, 08:07 AM   #21
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Hi everyone,

I don't know how i managed to blow the power stage,i was just adding 2*electrolytic capacitors on the secondary (2*4700uF//2*1000uF) then startup and blowing of the irf740 and ir2113.

N-channel,
my 12V auxiliary supply comes from a 50Hz,3.2VA transformer+bridge+reg 7812, which is onboard.
I'd like to get rid of this supply by using an auxiliary winding and a startup module as you did.
I'd like to know how the auxiliary winding blocks the startup process.
There must be a huge dissipation during startup (fortunately fast i suppose)

Eva,
I've tried to replace IR2113 (I don't have anymore,and i don't want to replace it everytime a failure occurs) by a transformer to feed the gates (12turns:12+12) with different kind of small toroid cores but with no success (no signal on the secondary...)
Could you tell me a little more about transformer gate control
(type of core,size...)
SG3525 delivers a square signal(+10V;-10V) with 10%deadtime between pin 11 & pin 14.

Thanks for your international support !
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Old 26th March 2006, 12:35 PM   #22
mzzj is offline mzzj  Finland
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Quote:
Originally posted by alexclaire
Hi everyone,


transformer to feed the gates (12turns:12+12) with different kind of small toroid cores but with no success (no signal on the secondary...)
Maybe you was using toroid from some sort of inductor? Iron-powder&MPP and similar low permeability materials dont work in gate transformers.

You need high-permeability toroid core with something like 0.5 square cm cross-section. Most of usual ferrite materials like 3c85 and 3c92 can be used.
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Old 26th March 2006, 04:27 PM   #23
subwo1 is offline subwo1  United States
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alexclaire,

At least for experimentation, you can buffer the outputs of your IR2113 with either emitter followers or IRF7343 dual N/P channel MOSFETs. You can use the easy source follower configuration with the IRF7343 since it has such low threshold voltage figures. Once I used the latter method, I was able to blow lots of IRF840's without blowing my IR2113. I think you should be able to use a resistor in series with the N-Ch gate to slow down the turn-on if needed. The IRF7343 is one of the few surface mount devices I have used much at all, and the SO-8 is the smallest I use, but only for MOSFETs.
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Old 26th March 2006, 08:18 PM   #24
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Alex,

I was able to "turn off' the zener-pass regulator ckt by setting its output voltage 4-5V lower than the output from the auxiliary winding, ~16V, so this back-bias of the 1N4001 diode (in series between the TIP50's emitter and the Vcc pin of the '3525) effectively shuts off the pass regulator. Since the zener reference gets its power from the +320V bus via two 220kW resaistors in series, the power dissipated by them is minimal (on the order of ~20mW), so no big deal there. Since the big dropping resistor is two 8.2kW 5W resistors in series from the +320V bus, this dissipates ~5-6W for only a few seconds, if that long. Once the TIP50 is biased off, it no longer dissipates any power, so this is how it shuts off.

Joe-

I like the idea you present regarding high-current buffering of the IR2113's outputs to keep them from blowing. I shoild look into this. I am suprised, however, since both Motorola and IR rated the 2113s outputs into +/-2A.

Steve
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Old 26th March 2006, 09:04 PM   #25
subwo1 is offline subwo1  United States
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Steve,

I think it is because those two amps can only pass through the chip for a short time. The internal resistance of the outputs of the IR2113 is several ohms. 2^2 * 7 is 28 watts. The chip will blow in a few milliseconds at that power dissipation level. The buffers are rated over twenty amps continuous--a very great difference. They even protect the outputs from negative voltage because of their body diodes.
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Old 26th March 2006, 10:38 PM   #26
subwo1 is offline subwo1  United States
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Quote:
They even protect the outputs from negative voltage because of their body diodes
Oops, I meant reverse voltage.
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Old 26th March 2006, 10:39 PM   #27
mzzj is offline mzzj  Finland
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Quote:
Originally posted by subwo1
Steve,

I think it is because those two amps can only pass through the chip for a short time. The internal resistance of the outputs of the IR2113 is several ohms. 2^2 * 7 is 28 watts. The chip will blow in a few milliseconds at that power dissipation level. The buffers are rated over twenty amps continuous--a very great difference. They even protect the outputs from negative voltage because of their body diodes.
Maybe one reason for blow-ups is trace inductance on driver chip output? Output voltage kicks below ground and intrisic thyristor mode self-destruct activates?

UC2825 controller for example has +-2A outputs, but all hell breaks loose if you try to drive something with it without schottky clamping diodes on output. I consider these high-current outputs pretty much useless as they require bulky 3A low-Vf schotkys on output to keep them alive.
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Old 26th March 2006, 10:59 PM   #28
subwo1 is offline subwo1  United States
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mzzj,
Your thoughts make sense. I have used that protection method, but I feel that the IRF4373 source follower buffer method is better in many ways, including compactness. The source followers protect the chip from having to to drive excessively low DC impedances like shorted gates, too. I have used 1 amp Schottkys instead of 3 amp ones, but they may not give enough protection compared to the 3 amp ones. However, once I thought of the IRF4373 source follower buffer way, I was hooked on it since it does the job of the Schottkys and more.
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Old 26th March 2006, 11:03 PM   #29
Eva is offline Eva  Spain
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That's why I got IR2112. Their drivers are rated only at 200mA but I don't conceive such an application without an external gate buffer stage and also these ICs were cheaper

But then, if I have a gate buffer, I can use a transformer to power it and drive it ...
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Old 26th March 2006, 11:05 PM   #30
subwo1 is offline subwo1  United States
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Also, now that I only use the ZVS approach to power supply design, I simply buffer the IR2113 with a 1000 ohm resistor on its outputs. Those resistors pass drive to a diode/PNP combination before each IRF840 MOSFET gate.
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