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Feedback for low frequency PWM regulator

You design like a TI apps. engineer, lots of silicon. Let's see a schematic so we can remove parts. The UCC2803 is a good choice. At your switching frequency, 250Hz, only

1.0mA is needed for supply current. So with input voltage from 30VDC to 50VDC, a 18K/0.25W resistor will suffice, no regulator is needed. 10K< Rt100mS. What happened to the other members of this NG? Do I have to do a complete design here? This is turning into my day job with no benefits. JF could do this with some 555s. Any more help will require good Tequila. Cheers, Harry
Reply to
HarryD
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Ahh Harry, you're back. Just couldn't stand idly by and watch me wallow in incompetence. Thus far I've just been Looking for uc3843 chips like the 2803 that have the lower voltage range I 've been looking for. The ucc2803 has the lower UVLO that I need and you say it should be fine. Great. All I have are hand drawn schematics at the moment. I was going to order some components and build your design and start fiddling with it. For a softstart, using linear regulators at least, you can produce a softstart but holding down the Vref with a capacitor. But your design has the Vref switched by the BSS84. I'd have to figure out what's going on there. From your design, it looks like I can adjust output voltage by varying the values of the R5s (46.4K and 13.3K)

Reply to
JMini

Ok, ok, updated schematic posted on ABSE with the UCC2803 and soft start added. Q2 (BSS84) is not controlling VR, it is controlling Q3. That is how we generate the voltage ramp for VFF control.

Cheers, Harry

Reply to
HarryD

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