Hello All
I am designing a ultrasound pulsing circuit using an H-bridge configuration with around 500V DC bus at a frequency of 100 kHz. The current required for the design is a pulsed peak of 12A. However, since this is a pulsed application, my average power is less than 5W.
I have my power source as a low-current (mA) high-voltage power supply trickle-charging a capacitor of 200 uF, which supplies the energy required during the ON time.
I am using the IR2110 as the driver in standard bootstrap configuration with a 12V Vccand my N-ch mosfets have been: IRFS9N60A, IRF830AS, FQB3N60C, and similar ST mosfets.
Every time, I see the same scenario: With my H-bridge disabled, I see the full 500V on the DC bus. Once the circuit starts switching, I see only around 300-325V across the load. Since ultrasonic excitation depends a lot on peak voltage, this is causing a huge deficiency on ultrasonic signal. However, I do not see any big tell-tale signs of trouble, like over-heating of mosfets, or pronounced droop in the voltage waveform or any HF oscillations. My dead-time is as high as 400 ns to prevent shoot-thru and my inputs are opto-isolated -- there is no RF noise to speak of. So, I am really confused here.
The things I thought could be wrong were:
1) ESR of my storage caps~ they are around 500 mOhm
2) Insufficient gate drive causing high drop across mofet -- not verified yet, but from IRF tech support, I should have no problems driving small mosfets like IRF820 with the IR2110. Also, I do not see any heat from the mosfets and the performance does not degrade with increase in operating frequency.
3) Bootstrap cap - again, I have low ESR tantalum cap in parallel with series ceramic cap -which meets teh guidelines.
I am sure the has to be something I have missed here, so I would appreciate any comments regarding my circuit and any tests i could try to narrow my problem area. I have compared my design to a legacy design by another manufacturer operating at 500V and it does not exhibit any voltage loss across the very same load.
Thanks in advance.
I am designing a ultrasound pulsing circuit using an H-bridge configuration with around 500V DC bus at a frequency of 100 kHz. The current required for the design is a pulsed peak of 12A. However, since this is a pulsed application, my average power is less than 5W.
I have my power source as a low-current (mA) high-voltage power supply trickle-charging a capacitor of 200 uF, which supplies the energy required during the ON time.
I am using the IR2110 as the driver in standard bootstrap configuration with a 12V Vccand my N-ch mosfets have been: IRFS9N60A, IRF830AS, FQB3N60C, and similar ST mosfets.
Every time, I see the same scenario: With my H-bridge disabled, I see the full 500V on the DC bus. Once the circuit starts switching, I see only around 300-325V across the load. Since ultrasonic excitation depends a lot on peak voltage, this is causing a huge deficiency on ultrasonic signal. However, I do not see any big tell-tale signs of trouble, like over-heating of mosfets, or pronounced droop in the voltage waveform or any HF oscillations. My dead-time is as high as 400 ns to prevent shoot-thru and my inputs are opto-isolated -- there is no RF noise to speak of. So, I am really confused here.
The things I thought could be wrong were:
1) ESR of my storage caps~ they are around 500 mOhm
2) Insufficient gate drive causing high drop across mofet -- not verified yet, but from IRF tech support, I should have no problems driving small mosfets like IRF820 with the IR2110. Also, I do not see any heat from the mosfets and the performance does not degrade with increase in operating frequency.
3) Bootstrap cap - again, I have low ESR tantalum cap in parallel with series ceramic cap -which meets teh guidelines.
I am sure the has to be something I have missed here, so I would appreciate any comments regarding my circuit and any tests i could try to narrow my problem area. I have compared my design to a legacy design by another manufacturer operating at 500V and it does not exhibit any voltage loss across the very same load.
Thanks in advance.