Re: H-BRIDGE and DC-SERVO DRIVE improvement help!

check out,

http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/h-
bridge.htm

I'm not sure about the speed of switching for the transistors, but it
appears that you are not addressing any back EMF unless it is handled
by the darlintons.

and it if I am not mistaken, MOSFET's will be easy to size for the
voltage and amps.

Also, what software are you using ? and what dwell time do you have
for the on time and off time between pulses ?

Dave




--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Asim Khan" <asimtec@y...>
wrote:

> Hi forum:
>
> I had build the H-Bridge by looking at this following
> design:
>
> http://cet.ssu.portsmouth.oh.us/~jlindeman/h-bridge/hbridge.html
>
> This above design uses PNP and NPN DARLINTON BJTS TIP12X series in
> its
> design. This design works ok as far as the switching frequesny
> applied is no more than 3~4Khz. I had put it in an application

where

> the PWM freqyncy is 11.7KHz. at high frequenies this design fails,
> burning transistors.
> I had tested this desin in my lab and i found that when you drive

the

> left PNP darlinton and the right NPN darlinton by appliying the PWM
> signal at left side then the right side PNP darlinton starts

getting

> heat up, when the PWM frequency is 10~20Khz, and eventually the

right

> side PNP darlinton blasts!!
> It seems the the right side PNP darlinton recieves the driving

pulses

> when it should not get driven. since in an hbridge at a single

moment

> there only two transistors should conduct, and in my case 3
> transitors starts conducting which causes so much high current
> through the transitor.
> same happens when i apply the PWM signal at right hand side, but

this

> time the left side PNP darlinton starts getting heatup
>
> I had also tried MJ11032(NPN) AND MJ11033(PNP) darlinton high speed
> switch transistors(specially designed for hi amp inductive load
> swithching) with 50AMP continuos current capability in my
> circuit. but observations were the same.
> I need to design a professional dc-servo drive which can operate

upto

> 80V and can deleiver around 20-30AMP.
>
> please suggest what changes should i made in this schematic so that
> i can use this H-BRIDGE design for HI frequency PWM signals and for
> hi amp loads !
> i request everyone to please suggest me any designs and or links
> best regards
> @sim