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

Harvey White wrote:

>On Tue, 06 May 2003 06:24:45 -0000, you 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
>>
>>
>>
><snip>
>
>
>>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
>>
>>
>
>You have what's effectively a 3 transistor darlington. Those are
>guaranteed to be slow. Darlingtons themselves are slow.
>
>How to fix: 1: try putting more current through the 2n2222
>transistors by reducing the values of R1 and R2 to 10 K ohms, and
>putting a 10K ohm resistor from each base of the upper darlington to
>the supply voltage.
>
>2) the real problem is that the turn on for the opposite transistor
>pair happens too quickly. You want some dead time in between the turn
>off for A and the turn on for B, and vice versa.
>

Ah, of course! An RC delay in the turn-off of the lower driver
transistors will help
a lot.

>
>If you are generating the phase waveforms by a computer/microprocessor
>then adjust your timing accordingly. If you are running this with a
>pulse generator, then I'd (rather reluctantly) suggest monostables
>(74LS122 or equivalent) and some gates to hold the opposing motor
>pulse off....
>
>for instance, if you want to shorten phase b, then look for the motor
>A turnoff, and and the monostable's output with phase B's input,
>holding phase b in an inactive state. Not elegant, but a way to go.
>
>

I use this in MY PWM servo amp, in fact. it is a simple RC with a diode
to speed up
the turn off, while the RC delays the turn on. It could probably be
used here, too.

Jon