PWM chip with constant impulse time ?

[forest]

Hi


I have a question for experienced electronic gurus here :


Do you know any chip which is working similiar to SG3525 or any other PWM , but with fixed (which can be set by user) ON time , while managing output voltage (like in DC-DC converters using voltage divider feedback) but with variable OFF time (and thus variable frequency) ?
Is there a known method of such kind of building DC converters ? How is that kind called ?


MarkE ? TinselKoala ? Somebody ?

[picowatt]

Hi


I have a question for experienced electronic gurus here :


Do you know any chip which is working similiar to SG3525 or any other PWM , but with fixed (which can be set by user) ON time , while managing output voltage (like in DC-DC converters using voltage divider feedback) but with variable OFF time (and thus variable frequency) ?
Is there a known method of such kind of building DC converters ? How is that kind called ?


MarkE ? TinselKoala ? Somebody ?

Pulse Frequency Modulation  (PFM)

http://www.digikey.com/en/articles/techzone/2014/mar/the-advantages-of-pulse-frequency-modulation-for-dc-dc-switching-voltage-converters

[forest]

Thanks picowatt


Do you know any simple popular pure PFM chip ?
Do you know if voltage regulation feedback loop in  PFM mode can be made using software code inside such microcontrollers as Attiny or Atmega ? Any code for that ? Mainly I wonder how to implement load regulation in case somebody switched off/on most of load and overvoltage on output capacitor should be prevented.

[Drak]

Hi forest,

I'm building a switching power supply using AVR's and other helper chips (mostly out of boredom). The ATtiny26 can PWM out at 250khz. I'm using an ATmega168p to control the ATtiny26's on time 0-255. If you want faster pwm than that you will either have to sacrifice resolution or choose a different chip.

[forest]

Drak


Maybe, but I'm not using PWM nor plan to use it (Well, maybe if I investigate it deeper to find the way to limit ON time width).
Thanks.PFM is exacly what I want with analog pin watching output capacitor voltage. Seems a lot of hacking before me to implement correct code :-)