The obvious problem with the schematic you linked to is that it uses pullup resistors to turn the mosfets on, instead of active drivers. This will cause the mosfets to turn on slowly, resulting in a significant amount of energy dissipated in each mosfet each time it is turned on. You may get away with this at low PWM frequencies, but you won't at high frequencies.Building high power H-bridges using discrete components is a bad idea. Either use an all-in-one mosfet-based H-bridge chip (if you can get one with sufficient voltage and current rating for your motor), or use half-bridge mosfet driver chips driving power mosfets. These chips provide active drive to the mosfets in both directions, and have shoot-through protection. However, many of them depend on the PWM to the high-side mosfet being less than 100% in order to generate the boost voltage needed to drive a high-side N-channel mosfet.
A DIY H-bridge discussion.http://forum.arduino.cc/index.php?topic=53425.0
What voltage do you want to drive the motor at, and what country are you in?
How about this http://si.farnell.com/allegro-microsystems/a3959sb-t/motor-driver-full-bridge-pwm-smd/dp/1521714?Ntt=a3959 or this http://si.farnell.com/stmicroelectronics/l6206n/ic-full-bridge-driver-dmos-dip24/dp/1271018 ?
Thanks for suggestions. I only found IC A3959SB-T in one store, and its currently not available. Looks like ill have to order from Farnell if I decide for gate driver (they are not cheap ).
But I think I'm gonna try burning some more MOSFETs first before I give up on that cheap design Someone said he got it to work at 15 kHz (I added a picture to my upper post). If I knew which values to look at I would try to calculate if its even possible (worth attempting). There are so many values for "gate capacitance", and then there's "gate charge". So confusing :S I know that I shouldn't save money on this, but... I was really hoping I could make use of my new Weller WS-81 instead of buying expensive pre-made stuff. You know, beginner's drive and excitement to make something I havent really realised yet whats possible to make at home and whats not...
or use half-bridge mosfet driver chips driving power mosfets. These chips provide active drive to the mosfets in both directions, and have shoot-through protection.
If it runs almost cold at 15kHz with 10K gate pullup resistors with the capacitor removed, then you could try reducing the four gate pullup resistors to 2.2K, and leaving all the other resistors at 10K. Try this at 15kHz first, and if it runs just as cool or cooler, then try 31kHz.
Quote from: dc42 on Jul 26, 2013, 06:05 pmor use half-bridge mosfet driver chips driving power mosfets. These chips provide active drive to the mosfets in both directions, and have shoot-through protection. _Some_ of them have shoot-through protection, many have none...With 31kHz switching you'll definitely need high current MOSFET drivers to get good performance, as you areswitching on average every 16us - you'd aim for switch times of a few hundred ns or so.If you are switching large amounts of power you want high-current drivers anyway to prevent gate voltageexcursions from gate-drain capacitance (or zener diodes).