Hi everyone,
Currently I'm trying to make an half bridge converter with SG3525 and gate drive transformer. The converter is intended to charge a 60V lead acid battery pack.
Here is the schematic: View attachment SG3525-battery-charger.PDF
Charging control and protection circuit is not complete yet, so they are not mentioned in the schematic. Startup section is not also attached yet, currently the driver is running from a separate source. Feedback network is also open.
The final circuit will have IRFP460 MOSFET, but currently I'm checking with IRF740. Bellow are the gate signal. These were captured while the main power is off, only the driver chip was running. At first I made a basic gate driver circuit. Only a 10 Ohm gate resistor was connected in series after the GDT. But the signal was too slow, raise time was more than 600ns. Then I attached the diodes and transistors, and the signal improved. Don't know if it is sufficient though.
After assembling everything, I've powered up the converter and that was a complete fail.
Finally I've moved to full 220VAC and it failed again. But this time I noticed some interesting things.
Can you please help me to solve this problem?
I've no more IRF740 or other high voltage FETs remain and have only two IRFP460 in another running converter. There is no way to get them now due to the current Corona virus lock-down situation. So I don't want to destroy them. But I've a lots of IRFP4321pbf (150V, 78A), so if you need any scope data while running on low voltage, I can provide that.
Here is my transformer details:
Thanks in advance
Regards,
Sukdeb Biswas.
Currently I'm trying to make an half bridge converter with SG3525 and gate drive transformer. The converter is intended to charge a 60V lead acid battery pack.
Here is the schematic: View attachment SG3525-battery-charger.PDF
Charging control and protection circuit is not complete yet, so they are not mentioned in the schematic. Startup section is not also attached yet, currently the driver is running from a separate source. Feedback network is also open.
The final circuit will have IRFP460 MOSFET, but currently I'm checking with IRF740. Bellow are the gate signal. These were captured while the main power is off, only the driver chip was running. At first I made a basic gate driver circuit. Only a 10 Ohm gate resistor was connected in series after the GDT. But the signal was too slow, raise time was more than 600ns. Then I attached the diodes and transistors, and the signal improved. Don't know if it is sufficient though.
After assembling everything, I've powered up the converter and that was a complete fail.
- First I've charged the primary bulk capacitor while driver was off, then unplugged the converter, and started the driver. It seems everything is ok, the converter run and tried to push some voltage to the secondary, unless the bulk capacitor discharged.
- I did it several time to make sure that everything is working.
- After that I powered up the converter and started the driver while power is on. Upper MOSFET shorted instantly.
- After changing the FET, I did it again and that MOSFET shorted again.
- After changing the MOSFET for the third time, I lowered the input voltage to 90VAC with a variac. Everything run perfectly. No MOSFET blown or shorted.
- Then I've increased the input to 150VAC then 170VAC and tested every time. In 170VAC, I've loaded the converter with around 100W load, nothing went wrong. During the test, I was measuring the Vds of high side FET. it was nice and clean, no noise or spike was present there.
Finally I've moved to full 220VAC and it failed again. But this time I noticed some interesting things.
- This time the converter didn't failed instantly, survived a couple of seconds.
- A 100W lamp was connected in series with the main supply from the beginning of testing. An oscilloscope probe was also connected to drain and source of the high side FET to measure the Vds.
- After starting the driver that series lamp started to oscillate roughly around 0 to 25% visual brightness. It didn't happen before. That Vds on the oscilloscope also indicated the oscillation. Didn't managed to measure though.
- Within 2-3 seconds I heard a pop sound and everything stopped, series lamp indicated a full short circuit.
- I measured everything again, these time all two MOSFET along with those two pnp transistor has shorted.
Can you please help me to solve this problem?
I've no more IRF740 or other high voltage FETs remain and have only two IRFP460 in another running converter. There is no way to get them now due to the current Corona virus lock-down situation. So I don't want to destroy them. But I've a lots of IRFP4321pbf (150V, 78A), so if you need any scope data while running on low voltage, I can provide that.
Here is my transformer details:
Main transformer:
- Core: EE55
- Primary: 9 Truns, 28SWG X 15
- Secondary: 7 Turns, 28SWG X 15
- Auxiliary: 1 Turn, 28SWG X 1
- Airgap: none.
Gate Driver transformer:
- Core: EE25
- Primary: 20 Truns, 28SWG X 2
- Secondaries: 20 Turns, 28SWG X 1 X 2 (Bifilar)
- Airgap: none.
Thanks in advance
Regards,
Sukdeb Biswas.
Last edited: