600VAC input problem with INN2904 and stackfet - OVP Latch?
I've designed and tested a 600VAC supply built around the INN2904. To reduce the voltage across the internal FET, I added a series FET above it as described in some of the stackfet reference designs.
It works fine until I get to about 420VAC. Above that voltage, on startup, some fault is triggered and the controller never begins switching. Interestingly, if I start the device below 420VAC, then increase the input voltage to 600VAC, it runs perfectly.
I have 11Mohm on the "V" pin, which does seem appropriate. I've tried bypassing the the under/overvoltage monitor altogether by shorting V to BPP, but no change.
I don't see the device attempting the timed "auto-restart", so I assume that the internal OVP Latch on the bias supply is getting triggered due to some sort of spike. I put a choke on the BPP pin - didn't help.
So, I think maybe the spike is entering at the Drain pin during startup - that's the power source (through the 5.95 regulator) until the bias switcher gets going. I'm waiting on a special scope probe to be able to monitor the D pin. In the meantime, I think my next effort will be to "soft-start" the power input with an inrush current limiter.
Any thoughts anybody?
Comments
The problem was not the OVP latch, it was the OV current into the V pin. THe datasheet states 77.5uA, but I think it's tripping at about 50uA. For example, with 600VDC after the ac rectification, I had a total of 13M ohms and it would trip, but 15.3M and it doesn't trip. Of course, now I have an issue with UV at 120VAC in, so I'll probably have to bypass the UV/OV altogether.
Anyway, my regulator starts reliably now, I'm mostly happy.
Hi,
Can you send me the date code and lot code of the device that you are using?
Could you also share the complete schematic of your power supply?
Regards,
PI-NANO
Date code = 1627
Regarding the schematic: although I haven't done anything too innovative in it, I'm a little shy since I'm a design consultant. I'll check with client before I do that.
Is it possible to send a schematic for engineering reveiw without posting publicly here? I understand it helps others when my problems are resolved, but I have NDA concerns with clients.
I'm also gettin' weird start-up issues with INN2904K (based on some modifications of the RDR-531), some ICs start fine, and some don't. How do I send a particular schematic file?
Datecode = 1627 (same as above)
I see the following: if the dV/dt of the DC bus voltage is a little bit higher than some value (under load), the INN2904K shutdown at some higher voltage, than the normal if the power supply is unloaded. (Ex. Under load the shutdown voltage of the DC bus is 150V, and without load the DC bus shutdown voltage is 80V), thats very weird. In both situations the Vbpp stays at the same 5.95V.
I'm attaching the waveforms of the Vbus and output voltage for 100% load (shutdown Voltage ~ 236V) and 50% load (shutdown Voltage ~ 44V)
| Attachment | Size |
|---|---|
| 50% load. CH1 => Vbus, CH2 => Output voltage (3.06 MB) | 3.06 MB |
| 100% load. CH1 => Vbus, CH2 => Output voltage (3.16 MB) | 3.16 MB |
Found that the BPP pin is the entire trouble-maker. I guess the OVP latch (Page 2 of the INN datasheet) does not have a deglitch filter, so any tiny current spike on this pin will trigger the OVP latch killing the entire power supply.
Disabled the pin, just leave the Cbpp capacitor there and it will be fine.
Daniel.
I bypassed the common mode choke on the input and the supply starts up fine at 600VAC. So I do think I'm getting an inductive spike on turn-on. See attached pic.
[edit] er, well it worked one time, but now back to shutting down.