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Unread 24-04-2008, 21:13
B.Johnston B.Johnston is offline
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Re: Victor logistics.

Victors actually do two things to control their load.
Vary the duration of an output pulse and control the polarity
(For the purpose of simplicity I may omit actual values and substitute simpler forms.)

They evaluate the length of the input pulse. i.e. 1ms to 2ms is the range of duration, with a frequency of about 40 cycles per second. If 1.5ms is the middle value a duration greater than this will produce a short full voltage pulse at the output. Keeping the math simple: a 1.6ms pulse input produces a 12V pulse of 5ms duration 40 times a second. A 2.0ms pulse input produces a 12V pulse of 25ms duration 40 times a second. If you cheat and do the math I'd hear you say “hey wait a minute, for a 2ms pulse this thing always puts out 12V” and I’d agree.
Now for pulses less than 1.5ms the victor swithes the + and – polarity and adjusts the output pulse length in the same fashion.

The Transistors in the H bridge are switched on and off at a varying duty cycle which produces the variable power needed to adjust the motor speed.

In the following diagram the red trace is the pwm input, the blue trace is the pulsed output and the green trace is the output power averaged over the25ms period.
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