zombiess
10 MW
Not sure if anyone here has taken the time to go through and make these measurements before, I know I've searched and I didn't see them so I thought I'd post up my info I gathered today while checking out the controller. This controller is heavily modded, details covered in this thread http://endless-sphere.com/forums/viewtopic.php?f=2&t=37166
I built an EB236-AS-1 from scratch with some thermal mods and also extra heat sinking by tying all the tabs together with buss bars. It uses 6 individual 0 ohm gate resistors to each FET gate.
Now on to the scope info. Hooked it up to monitor the driver and see how slow the switching performance is. Here are the pictures I took of my scope while testing. I'm using a 510 ohm resistor for R115 and the on board switching power supply was producing a solid 20V. The regulators were outputting 5V and 15V respectively. Maximum gate drive voltage seen was 15V. Not sure if the R115 resistor being so high has any effect on this, I didn't bother measuring the 15 regulator for ripple current to see if it was holding up to the current load being placed on it by the drivers due to being run on 12S instead of 30S with such a large limiting resistor. I'll probably try to check that tomorrow to verify that a 510 ohm R115 resistor isn't causing me any issues with the lower voltage I'm testing at.
This board was built with IRFB4115 FETs all miller plateau matched at 4.0V Vgs to maximize synchronous switching to maximize current sharing.
First thing I discovered is that PWM switching frequency is 15,875hz. This is the really ugly gate drive signal at part throttle (probably caused by me under powering the on board power supply) showing the total time on and time off giving a total period of 63uS. It should look more like a square wave.
At 100% throttle there is zero PWM occurring. This is phase A at 100% throttle showing the 15V gate signal and commutation period. Wheel was going 26.1 MPH on 46.1V of battery power.
This is a close up of the gate turning on, you can see the Miller Plateau occurring right around 5V which is right around where I measured it on this bank when i was testing the FETs. Spec sheet shows it happening around 6.0V but these seem to happen 1V lower. It takes about 2.6uS to reach the miller plateau. Hangs out on the plateau for 2.2uS then continues on to fully turned on around 7.0V. I actually measured the full turn on right around 5.0V. It takes about 5.6uS to go from 0V to 7V and 4.8uS to go from 0V to 6V and 2.5uS to go 0V to 5V which should be close to full on based on what I measured on many of the IRFB4115 FETs I have and sampled randomly, unless I measured incorrectly.
The total time to transition from 0V to the full 15V gate drive voltage is a long 27uS.
Turn off time is about 4.6uS to drop from 15V down to 0V and about 2uS to drop to the point where it should be off.
I'm wondering if the switching speeds in the IRFB4110's might be a little slower because they have about double the Qg nC (total gate charge) causing them to switch slower. I did measure the IRFB4110s I have appear to fully turn on at 4.0V Vgs so they might not switch as slow as I think.
I hope this info helps some of you guys building controllers and playing with the Xie Chang boards. Conclusions is the EB2xx driver leaves a lot to be desired, but also to be noted is the devices appeared to perform much better than their spec sheet suggests. I'm guessing this better performance is one of the reasons we can get away with abusing these controllers so much.
Question for those in the know, since the resistance is linear in relation to Vgs and the resistance is really high at low Vgs the FETs won't produce much heat since they are essentially current limited. Is this why the controllers work as well as they do even with such slow switching times or am I missing something? Any suggestions to improve the switching times of the stock config without substituting an entire new driver board? The 6 individual gate resistors are already at 0 ohms would bridging them int a pure parallel config help any? I really should test at a higher supply voltage or bypass the R115 resistor to verify the on board power supply isn't current limiting the driver circuitry and scope it again to see if there is any difference.
I'm no expert on any of this so please don't take this as 100% correct, I'm only posting what information I have measured and know so hopefully some real experts such as Rhitee05, Bigmoose or Electroglide will chime in with their thoughts.
I built an EB236-AS-1 from scratch with some thermal mods and also extra heat sinking by tying all the tabs together with buss bars. It uses 6 individual 0 ohm gate resistors to each FET gate.
Now on to the scope info. Hooked it up to monitor the driver and see how slow the switching performance is. Here are the pictures I took of my scope while testing. I'm using a 510 ohm resistor for R115 and the on board switching power supply was producing a solid 20V. The regulators were outputting 5V and 15V respectively. Maximum gate drive voltage seen was 15V. Not sure if the R115 resistor being so high has any effect on this, I didn't bother measuring the 15 regulator for ripple current to see if it was holding up to the current load being placed on it by the drivers due to being run on 12S instead of 30S with such a large limiting resistor. I'll probably try to check that tomorrow to verify that a 510 ohm R115 resistor isn't causing me any issues with the lower voltage I'm testing at.
This board was built with IRFB4115 FETs all miller plateau matched at 4.0V Vgs to maximize synchronous switching to maximize current sharing.
First thing I discovered is that PWM switching frequency is 15,875hz. This is the really ugly gate drive signal at part throttle (probably caused by me under powering the on board power supply) showing the total time on and time off giving a total period of 63uS. It should look more like a square wave.
At 100% throttle there is zero PWM occurring. This is phase A at 100% throttle showing the 15V gate signal and commutation period. Wheel was going 26.1 MPH on 46.1V of battery power.
This is a close up of the gate turning on, you can see the Miller Plateau occurring right around 5V which is right around where I measured it on this bank when i was testing the FETs. Spec sheet shows it happening around 6.0V but these seem to happen 1V lower. It takes about 2.6uS to reach the miller plateau. Hangs out on the plateau for 2.2uS then continues on to fully turned on around 7.0V. I actually measured the full turn on right around 5.0V. It takes about 5.6uS to go from 0V to 7V and 4.8uS to go from 0V to 6V and 2.5uS to go 0V to 5V which should be close to full on based on what I measured on many of the IRFB4115 FETs I have and sampled randomly, unless I measured incorrectly.
The total time to transition from 0V to the full 15V gate drive voltage is a long 27uS.
Turn off time is about 4.6uS to drop from 15V down to 0V and about 2uS to drop to the point where it should be off.
I'm wondering if the switching speeds in the IRFB4110's might be a little slower because they have about double the Qg nC (total gate charge) causing them to switch slower. I did measure the IRFB4110s I have appear to fully turn on at 4.0V Vgs so they might not switch as slow as I think.
I hope this info helps some of you guys building controllers and playing with the Xie Chang boards. Conclusions is the EB2xx driver leaves a lot to be desired, but also to be noted is the devices appeared to perform much better than their spec sheet suggests. I'm guessing this better performance is one of the reasons we can get away with abusing these controllers so much.
Question for those in the know, since the resistance is linear in relation to Vgs and the resistance is really high at low Vgs the FETs won't produce much heat since they are essentially current limited. Is this why the controllers work as well as they do even with such slow switching times or am I missing something? Any suggestions to improve the switching times of the stock config without substituting an entire new driver board? The 6 individual gate resistors are already at 0 ohms would bridging them int a pure parallel config help any? I really should test at a higher supply voltage or bypass the R115 resistor to verify the on board power supply isn't current limiting the driver circuitry and scope it again to see if there is any difference.
I'm no expert on any of this so please don't take this as 100% correct, I'm only posting what information I have measured and know so hopefully some real experts such as Rhitee05, Bigmoose or Electroglide will chime in with their thoughts.