Electrical – Positive to negative PWM converter


I am looking for a way to convert a + 24V square wave coming from a cnc controller, to -5V. The frequency of a square wave will vary from 15kHz to 35kHz.

What methods would you suggest?

Thanks for your attention.

Best Answer

Take your 24V pulses and strongly differentiate them with an RC high pass filter: -

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Make sure they are properly differentiated like example (a) below: -

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The resistor shown above needs to be connected to -2.5 volts - maybe use two equal value resistors - one to 0V and one to -5V

Reduce the amplitude to 5Vp-p (resistors and/or diode clamps can do this)

Set up a schmitt trigger running from a -5V rail and feed the clamped signal to its input. The output from the schmitt trigger will be the PWM signal you want. It needs to be a schmitt trigger so that it only changes state when a spike occurs: -

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