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Oscillator Help?

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Alexsgarage

New Member
I need to build an oscillator to produce a square wave to drive an inverter. The waveform will need to have a dead time of 200 ns to allow for the IGBTs to turn off. The waveform will have a period of 7692 ns, the frequency is 130 kHz. Can I use an SG3524 PWM to make this waveform?
 

Papabravo

Well-Known Member
The frequency is within the capability of the device using a timing capacitor of 0.001 to 0.002 uF with resistors in the 3K to 5K range.
e.g. 0.002 uF and 3.83K --> 7.66 usec --> 130,548 Hz.

A dead time of 200 nsec appears to be unrealizable as the shortest time documented is 500 ns with a .001 uF capacitor.

The output is a ramp from 1.5 to 3 Volts with the fall time determinign the dead zone.

This sounds like 7.16 usec on the ramp and 500 nsec dead time.

I think you will be close -- certainly worth experimenting with.

As an LTSpice fan I would encourage you to get the simulator and try it on your PC before investing time and money. Simulators are not the complete answer, but they do provide quick check on a devices capabilities.
 
Last edited:

Papabravo

Well-Known Member
How would I make this variable? The dead time is also what determines the duty cycle.
You would need a variable capacitor, since that is the component that determines the dead time. Have you read the datasheet? It is pretty clearly spelled out in quite unambiguous language. BTW if you need a square wave you'll have to add a comparator to the sawtooth output of this device.
 

Alexsgarage

New Member
Here is the waveform that I am trying to create. Can I use a PWM, I am asking because I am using the internal oscillator of an SG3524 PWM to generate the clock signal.
 

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