[TechAssist] Re: uc3843 PWM osc/driver in 8pin DIP
- From: "Ohio Consumer Electronics" <jj@xxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Wed, 15 Oct 2003 18:17:53 -0400
It uses an RC oscillator that may or may not be synchronized externally.
The osc pin can also be driven by a square wave from external source and no
RC components. That being said here are some tips for troubleshooting this
circuit.
Since it's a 43 I'm assuming it's a battery operated or secondary supply and
not an off-line supply. the VCC pin is pin7 and needs to be at least 8.5
volts before the chip will operate.
If the VCC is present check pin 8, it's the vref output and should be 5v.
If you get the 5v the chip is *probably* good.
The oscillator - pin 4 will have the timing components - a resistor to vref
and a cap to ground. You should be able to scope a waveform here even if
the output is off.
Pin 3 is the current sense input - measures voltage drop across a low ohm
resistor from the switch FET source to ground. The chip will not output any
pulses if this pin is above 1 volt.
If everything else looks good check the feedback parts off pin 2.
Good luck!
Joel Jacobs
Ohio Consumer Electronics
Pickerington, Ohio
----- Original Message -----
From: <majorthom@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, October 15, 2003 5:33 PM
Subject: [TechAssist] uc3843 PWM osc/driver in 8pin DIP
> Is this a free running osc. or does it get sync input? In other words,what
inputs aside from Vcc does the device require?
>
> Neal Electronics 1901 E Wm. Cannon,Austin,Tx Suite A295 tel.5126635051
Fax.5124438808
>
>
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