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Using a PWM controller UC2845 as a oscillator or force-driven output

  • Thread starter Klaus Vestergaard Kragelund
  • Start date
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Hi

I have this very cheap UC2845 device (TI device), which output drive can
handle high voltage and high current

www.microdesign.dk/tmp/uc2845.pdf

What I would like is to control the output of the device directly. Has
anyone tried this - perhaps driving the "Current Sense" and "Comp" pins in a
defined manor?

Furthermore migth it then be used a oscillator?

Thanks

Klaus
 
G

Genome

Jan 1, 1970
0
| Hi
|
| I have this very cheap UC2845 device (TI device), which output drive
can
| handle high voltage and high current
|
| www.microdesign.dk/tmp/uc2845.pdf
|
| What I would like is to control the output of the device directly. Has
| anyone tried this - perhaps driving the "Current Sense" and "Comp"
pins in a
| defined manor?
|
| Furthermore migth it then be used a oscillator?
|
| Thanks
|
| Klaus
|
|

If you want direct control of the output then, unfortunately, you have
to drive the RT/CT pin. Gate drive is turned off when the RT/CT pin
exceeds something like 2.7V. It is re-established when RT/CT falls to
about 1V. Bear in mind that there is an internal, 10mA(?), current sink
on the RT/CT pin when externally pulled high.

You lose the oscillator function.

DNA
 
T

Terry Given

Jan 1, 1970
0
Genome said:
| Hi
|
| I have this very cheap UC2845 device (TI device), which output drive
can
| handle high voltage and high current
|
| www.microdesign.dk/tmp/uc2845.pdf
|
| What I would like is to control the output of the device directly. Has
| anyone tried this - perhaps driving the "Current Sense" and "Comp"
pins in a
| defined manor?
|
| Furthermore migth it then be used a oscillator?
|
| Thanks
|
| Klaus
|
|

If you want direct control of the output then, unfortunately, you have
to drive the RT/CT pin. Gate drive is turned off when the RT/CT pin
exceeds something like 2.7V. It is re-established when RT/CT falls to
about 1V. Bear in mind that there is an internal, 10mA(?), current sink
on the RT/CT pin when externally pulled high.

You lose the oscillator function.

DNA

but there is a toggle flip-flop in the UC3845.....I have used about 50,000
UC3842 as IGBT gate drivers doing exactly this. I think the T FF will screw
things up though :)

Cheers
Terry
 
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