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

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.

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.

Harvey

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