CAD CAM EDM DRO - Yahoo Group Archive

Re: Chopper max voltage?

Posted by Steve Kelley
on 2000-10-08 13:22:29 UTC
--- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
<geckohall@h...> wrote:
> Hi,
>
> Here's my 2 cent's worth on the great chopper frequency debate. The
> choice of switching frequency is based on the best balance between
> two conflicting goals, motor losses vs. drive losses:
>
> 1) High frequency = low motor losses.
> 2) Low frequency = low drive losses.
>
> 1) Motor iron heating is caused by AC currents. Chopping
contributes
> to this by causing a "ripple current" AC component on top of the DC
> current passing thru the winding. The higher the amplitude of
> this "ripple current" the hotter the motor will get.
>
> The amplitude of this current is equal to V / 2fL. "V" is the power
> supply voltage, "L" is the motor inductance and "f" is the chopping
> frequency.
>
> The higher the chopping frequency "f", the lower the motor heating.
>
> 2) Transistors in a chopping drive get very hot when there is
> simultaneous high current and high voltage across them. This
happens
> breifly everytime the output changes from high to low or visa versa.
>
> This are called "switching losses", and the occur on every output
> change edge.
>
> Higher frequencies mean more edges per second, and thus more
heating
> in the drive transistors.
>
> The L297 uses Darlington output transistors. They have high gain
but
> are very slow in switching. They also have a high "on" voltage.
Both
> contribute to heating of the drive.
>
> Mariss
>
>
>
> P.S. Here's how an L298 compares to a MOSFET (IRF530) bridge at
24V,
> 2A and 20kHz:
>
> IRF530:
>
> Conductance losses (I squared R)= 4 X (.15 + .15) = 1.200W
> Switching losses 2f(IV)t = (2 X 20kHz X 24 X 2)100nS = .192W
> ------
> Total heating (spread out over 2 125W packages) 1.372W
>
> L298:
>
> Conductance losses (Von times Icc) = (2.7 + 2.3)X 2 = 10.000W
> Switching losses 2f(IV)t = (2 X 20kHz X 24 X 2)1uS = 1.920W
> ------
> Total heating (in one 15W package) 11.920W

Greetings....

Mariss makes a good point about the RDSon-resistance of the Mosfet,
dictating the conductance losses. Lets take it one-step further and
add that...by spending another $1 inside the G201 , the driver would
not even need an extra heatsink. This is based on the IRF530's RDSon
of .11-ohms and the IRF540's RDSon of a mere .052-ohms. The losses
during conduction would drop to about half and given that at 20khz.
the bulk of the losses are conduction....it would truely drop total
losses to half. But, since the IRF530's total gate charge is only
44nC and the IRF540's being 94nC....there would be a slight drive
supply penalty. On the order of 4ma added to the entire dual-H Bridge.
Based on Qc(44nC)x F(20khz.)= .9ma for the IRF530 and Qc(94nC)x F
(20khz.)= 1.9ma for the IRF540. I'm sure this benefit would only hold
true up to about 6 amps/phase. But, it does bring about an
interesting question,that is,whether to spend inside or outside the
package. Either way,Mariss has a series of drivers that are a Marvel !

Regards....
Steve

Discussion Thread

Greg Nuspel 2000-10-03 15:47:00 UTC Chopper max voltage? Art Fenerty 2000-10-03 16:19:34 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? SNTLewis@a... 2000-10-03 18:03:06 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-03 21:59:24 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Greg Nuspel 2000-10-04 04:02:04 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-04 04:29:33 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Dan Mauch 2000-10-04 06:58:45 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Dan Mauch 2000-10-04 07:06:22 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Ian Wright 2000-10-04 08:27:56 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Mike 2000-10-04 09:41:09 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Henrik Olsson 2000-10-04 10:56:35 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-04 11:26:13 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-04 11:34:44 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Art Fenerty 2000-10-04 12:07:54 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Alan Marconett KM6VV 2000-10-04 12:13:40 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Alan Marconett KM6VV 2000-10-04 12:43:34 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? ballendo@y... 2000-10-04 14:26:42 UTC re:Re: Chopper max voltage? Mariss Freimanis 2000-10-04 15:43:22 UTC Re: Chopper max voltage? ballendo@y... 2000-10-04 16:17:59 UTC re:Re: Chopper max voltage? Mike 2000-10-04 16:46:15 UTC re:Re: Chopper max voltage? William Scalione 2000-10-04 20:32:30 UTC Re: [CAD_CAM_EDM_DRO] re:Re: Chopper max voltage? JanRwl@A... 2000-10-04 21:50:14 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Mariss Freimanis 2000-10-04 22:10:27 UTC Re: Chopper max voltage? JanRwl@A... 2000-10-04 22:29:40 UTC Re: [CAD_CAM_EDM_DRO] Re: Chopper max voltage? Jon Elson 2000-10-05 00:06:01 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-05 01:07:25 UTC Re: [CAD_CAM_EDM_DRO] Re: Chopper max voltage? Dan Mauch 2000-10-05 05:52:56 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Dan Mauch 2000-10-05 06:03:40 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Alan Marconett KM6VV 2000-10-05 11:05:54 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-05 11:44:38 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Art Fenerty 2000-10-05 12:29:35 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Kevin P. Martin 2000-10-05 12:58:07 UTC RE: [CAD_CAM_EDM_DRO] Chopper max voltage? Chris Hellyar 2000-10-05 23:51:14 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Dan Mauch 2000-10-06 07:03:22 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? stratton@m... 2000-10-06 07:57:22 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Alan Marconett KM6VV 2000-10-06 10:31:39 UTC Re: [CAD_CAM_EDM_DRO] Chopper max voltage? Randy Gordon-Gilmore 2000-10-07 13:30:49 UTC Sherline mill CNC mods? wanliker@a... 2000-10-07 14:38:32 UTC Re: [CAD_CAM_EDM_DRO] Sherline mill CNC mods? Randy Gordon-Gilmore 2000-10-07 19:44:47 UTC Free "zprint" Alan Marconett KM6VV 2000-10-08 13:17:43 UTC Re: [CAD_CAM_EDM_DRO] Sherline mill CNC mods? Steve Kelley 2000-10-08 13:22:29 UTC Re: Chopper max voltage? Anne Ogborn 2000-10-08 14:03:47 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" dave engvall 2000-10-09 09:00:58 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Anne Ogborn 2000-10-09 10:53:19 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Randy Gordon-Gilmore 2000-10-09 11:02:07 UTC Ideal 3D printer? Randy Gordon-Gilmore 2000-10-09 13:52:30 UTC Re: Sherline mill CNC mods? Jon Anderson 2000-10-09 14:19:05 UTC Re: [CAD_CAM_EDM_DRO] Re: Sherline mill CNC mods? dave engvall 2000-10-09 17:07:28 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Lee & Chris studley 2000-10-09 19:20:42 UTC Re: [CAD_CAM_EDM_DRO] Ideal 3D printer? Anne Ogborn 2000-10-10 10:18:34 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Andrew Werby 2000-10-10 11:12:59 UTC Re: Free "zprint" stratton@m... 2000-10-10 11:23:16 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" William Scalione 2000-10-10 11:49:49 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" Alan Marconett KM6VV 2000-10-10 12:11:51 UTC Re: Free "zprint" Anne Ogborn 2000-10-10 12:45:34 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" dave engvall 2000-10-10 12:46:28 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" Anne Ogborn 2000-10-10 12:50:17 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" William Scalione 2000-10-10 13:16:49 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" William Scalione 2000-10-10 13:20:27 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" Jeff DelPapa 2000-10-10 13:32:40 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" PMeinhard@a... 2000-10-10 13:35:40 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" Anne Ogborn 2000-10-10 18:51:59 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" Anne Ogborn 2000-10-10 18:57:24 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" diazden 2000-10-11 07:08:41 UTC Re: [CAD_CAM_EDM_DRO] Re: Free "zprint" JanRwl@A... 2000-10-13 21:30:33 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Anne Ogborn 2000-10-14 00:43:38 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" Alan Marconett KM6VV 2000-10-14 12:05:34 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint" dave engvall 2000-10-15 21:23:16 UTC Re: [CAD_CAM_EDM_DRO] Free "zprint"