Hi
Attached are schematics of a bidirectional AC voltage MOSFET based regulator.
dg1.jpg:
This is the power side. I've attached IRF840 datasheet for your immediate reference. This arrangement might work without the diodes. The diodes are present in the design for a future development when the MOSFETS will be replaced by IGBTs. These diodes will counter the internal parasitic diode effect of the IGBTs. But for now its only MOSFETs.
dg2.jpg:
This is the gate drive circuit. 4N35 isolates power from MCU. The TC4431 is a MOSFET driver from Microchip. I've attached that datasheet also. In that, Pins 6 and 7 are said to be sink and source outputs respectively. I've used the source output. Correct me if I'm wrong.
The MCU is progrmmed to give switching pulse for delay angle based control.
Experimental observation:
For testing purposes, I did not give more than 60Vrms as input.
The sequence of events:
1. With correct switching pattern across gate source(I checked these on a scope), both MOSFETS refuse to turn off. The Input voltage appears unmodified across the resistor.
2. Next I left the gates floating. Still the same result.
3. Suspecting that the gate is precharged, I shorted gate source (with the driver unit disconnected) with a wire. The MOSFET turns off instantly. But the moment I remove the wire, the device turns on gradually, within 2 seconds.
4. Previously I assumed that TC4431 has a discharge path in the off-state. Suspecting this assumption, I attached a 10k across gate-source, in addition to the driver. Now the devices wont turn on at all, irrespective of gate source voltage.
5. I replaced the MOSFETS. Same results.
Querries:
1. What is wrong?
2. Am I missing out anything from the 4431 datasheet? Am I using the chip correctly?
3. This is my first high-side switching. Should I add any other device for the special purpose of high-side switching? (TC4431 is a high side driver)
Thank You.
Attached are schematics of a bidirectional AC voltage MOSFET based regulator.
dg1.jpg:
This is the power side. I've attached IRF840 datasheet for your immediate reference. This arrangement might work without the diodes. The diodes are present in the design for a future development when the MOSFETS will be replaced by IGBTs. These diodes will counter the internal parasitic diode effect of the IGBTs. But for now its only MOSFETs.
dg2.jpg:
This is the gate drive circuit. 4N35 isolates power from MCU. The TC4431 is a MOSFET driver from Microchip. I've attached that datasheet also. In that, Pins 6 and 7 are said to be sink and source outputs respectively. I've used the source output. Correct me if I'm wrong.
The MCU is progrmmed to give switching pulse for delay angle based control.
Experimental observation:
For testing purposes, I did not give more than 60Vrms as input.
The sequence of events:
1. With correct switching pattern across gate source(I checked these on a scope), both MOSFETS refuse to turn off. The Input voltage appears unmodified across the resistor.
2. Next I left the gates floating. Still the same result.
3. Suspecting that the gate is precharged, I shorted gate source (with the driver unit disconnected) with a wire. The MOSFET turns off instantly. But the moment I remove the wire, the device turns on gradually, within 2 seconds.
4. Previously I assumed that TC4431 has a discharge path in the off-state. Suspecting this assumption, I attached a 10k across gate-source, in addition to the driver. Now the devices wont turn on at all, irrespective of gate source voltage.
5. I replaced the MOSFETS. Same results.
Querries:
1. What is wrong?
2. Am I missing out anything from the 4431 datasheet? Am I using the chip correctly?
3. This is my first high-side switching. Should I add any other device for the special purpose of high-side switching? (TC4431 is a high side driver)
Thank You.
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