Does PWM DC = half-wave AC ? - Electronic Circuits Projects Diagrams Free

liquidics · 2nd March 2006, 08:32 AM

If I toggle a DC source on and off does that generate a half-wave AC source or is there more to it?

Asjad · 2nd March 2006, 09:21 AM

Dear Friend,

In DC pulses the voltage only changes from 0v, to a positive voltage.
To get AC you would need to have say +5v, 0v and -5v

With PWM the time for one complete cycle varies, usually used for power control

Hope this helps

**Nigel Goodwin** · 2nd March 2006, 10:17 AM

This is an often argued point!.

As far as I'm concerned, switching DC ON and OFF provides AC, if you need it to go -ve and +ve then simply place a capacitor in series with it!.

This provides fullwave squarewave AC.

akg · 2nd March 2006, 11:14 AM

Quote:

Originally Posted by Asjad

Dear Friend,

In DC pulses the voltage only changes from 0v, to a positive voltage.
To get AC you would need to have say +5v, 0v and -5v

With PWM the time for one complete cycle varies, usually used for power control

Hope this helps

need not to be.. if there is a change in dc voltage wrt time , there is an ac component , all u need is a capacitor to block dc and get ac.

Styx · 2nd March 2006, 12:57 PM

Quote:

Originally Posted by liquidics

If I toggle a DC source on and off does that generate a half-wave AC source or is there more to it?

it produces a full-wave AC source with a DC-offset

liquidics · 2nd March 2006, 07:41 PM

Thanks all, I get it, PWM DC + Cap as DC filter = full-wave AC

What if I took a PIC MCU which has the ability to sink in the low state and set pin 1 and pin 2 to alternate pulses (1 high & 2 low then 2 high & 1 low) and ran a wire loop between the pins with a Cap in series, would that make a full-wave square-wave AC or a sine-wave because of the Cap? Would there be any benefit/difference to creating AC this way as opposed to a single PWM DC source with cap to ground?

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2nd March 2006, 08:32 AM	(permalink)
liquidics	Does PWM DC = half-wave AC ? If I toggle a DC source on and off does that generate a half-wave AC source or is there more to it?

2nd March 2006, 09:21 AM	(permalink)
Asjad	Correction Dear Friend, In DC pulses the voltage only changes from 0v, to a positive voltage. To get AC you would need to have say +5v, 0v and -5v With PWM the time for one complete cycle varies, usually used for power control Hope this helps __________________ Best Regards

2nd March 2006, 10:17 AM	(permalink)
Nigel Goodwin	This is an often argued point!. As far as I'm concerned, switching DC ON and OFF provides AC, if you need it to go -ve and +ve then simply place a capacitor in series with it!. This provides fullwave squarewave AC. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

2nd March 2006, 07:41 PM	(permalink)
liquidics	Thanks all, I get it, PWM DC + Cap as DC filter = full-wave AC What if I took a PIC MCU which has the ability to sink in the low state and set pin 1 and pin 2 to alternate pulses (1 high & 2 low then 2 high & 1 low) and ran a wire loop between the pins with a Cap in series, would that make a full-wave square-wave AC or a sine-wave because of the Cap? Would there be any benefit/difference to creating AC this way as opposed to a single PWM DC source with cap to ground?