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DE-865 Gate driver configuration

Posted by: gid204 on Sat, 07/24/2021


I was wondering the purpose of the NPN/PNP BJTs used driving the back to back MOSFETS for the load control in DER-865. Are you able to briefly explain why this configuration was used?
Could the MCU be directly connected to the MOSFETs or could a gate driver be used instead?

Thanks in advance.


Submitted by PI-Crumb on Tue, 07/27/2021


The MCU output does not have enough juice to drive the MOSFETs. Also, the MCU output is only 3V which is not enough to exceed the VGS threshold on some FETs. We used discrete driver (NPN/PNP) because they are usually cheaper than a dedicated gate driver IC. Also, we were able to reduce the standby current a little bit compared to dedicated ICs which have higher quiescent current. However, these gate driver ICs may offer additional features and simplify the design so it is also not a bad option to replace the discrete with gate driver IC.



Thank you for the clarification, this is what I imagined.

I was also thinking, without seeing the firmware - Are both MOSFETs turned on at the same time? I.e. Gate_Drive and Gate_Drive2 are turned on simultaneously?

Could these two connections become one, so that only one GPIO port from the MCU is used?



hi. We tried to demonstrate in the DER that it is possible to set to leading or trailing edge dimming mode. Single gate drive can be done on trailing-edge dimming. For leading-edge mode, it has to be driven separately in order to detect the logic transition properly. There are other ways to do it for leading edge, but we chose separate drivers after seeing that it gave us more flexibility in ensuring better compatibility with low-PF and high-PF bulbs.