| ??? 06/22/06 15:00 Modified: 06/22/06 15:03 Read: times |
#118856 - Strong Responding to: ???'s previous message |
Kai Klaas said:
This could be the reason for the MOSFETs becoming hot. Do the MOSFETs becoming hotter, when you omit the free wheeling diodes? Then, the internal body diode of MOSFET could be the reason. Become the free wheeling diodes warm? I'm not using any additional "freewheel diodes" anymore, just MUR820's across source and drain of IRL (these do not get warm at all). If driving mosfets to full enhancement does not lower IRL temperature, then internal diodes would then be the cause. In that case I'll just have to live with the heat I guess. Jon said:
Kai said:
Yes, but isn't it a bit strong? I would try some paralleled gates of CD4000 series to drive the MOSFETs. If driving the fets harder proves to lower temp, then I will try these... looks like it would be a lower cost solution. Kai said:
Take care, UGSmax of your IRL540 is +-10V. So, supply voltage of MOSFET driver should not exceed 7...8V. Then, you can even accept some negative going pulses at source pins of MOSFETs, where the sense resistors are connected to. Kai Yes, I will take care with supply of driver. On a different note... I want to be able to change to change the Vref voltage to lower current when motor is sitting idle, without using a DAC or digital pot, is there any simple discrete methods of switching between two different voltages or resistances with 1 port pin? Thanks Jon |
