Ubergeek63

Actually it is the nature of the regulator that changes the frequency and duty cycle. So you would not need any of that.

The video you link to seems to have nothing to do with your question other than some odd little comment about a gimmicky piecemeal regulator based on a dinosaur of a part.

The LM3485 is strictly a voltage regulator. He is looking to regulate current and you would be much better off with an HV9910 set up for constant off time regulation with and external FET driver.

Nowhere is the power source mentioned or what exactly is going on. Near as I can surmise, it appears that he is trying to run an engine off of hydrogen and the "cells" are generating hydrogen from water. Unfortunately the last thing I heard was that it takes more power to extract the hydrogen than you get from burning it.

skeeterb

Right now ZFF is using it as a booster to improve the MPG of his gasoline burning Toyota Tacoma. Like I said, he only mentioned it in passing when he posted one of his videos, I can't remember which one.

__________________
We are the BORG. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service US. RESISTANCE IS FUTILE

skeeterb

I'm just interested in controlling the frequency and duty cycle using solid-state components, not by using a bunch of pots and switches that could malfunction after a period of use and/or the environment in which it is situated. Looking again at the schematic of a PWM that I have, i know I would have to put it somewhere in the section where the controls for frequency and duty cycle are.



Edit:

I have found a PWM that uses Dip Switches to control the frequency and uses a pot to control the duty cycle. That would simplify my search for a method to self regulate the PWM. I have attached the PWM drawing that I found.

Attached Images

Pulse Width Modulator.JPG (388.3 KB, 7 views)

__________________
We are the BORG. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service US. RESISTANCE IS FUTILE

Ubergeek63

why not just look at a real PWM chip?

http://www.supertex.com/pdf/datasheets/HV9910.pdf maybe?

skeeterb

I looked at that chip and its interesting that a PWM can be achieved using that IC. How would one adjust the output of the PWM using the HV9910 IC?

__________________
We are the BORG. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service US. RESISTANCE IS FUTILE

Ubergeek63

You do not adjust the PWM, the 9910 adjusts in order to regulate the current.

You can put in a voltage on the LD (linear dimming- it is meant to drive power LEDs) pin to bring the peak voltage on the current sense down from 0.25V.

When the frequency adjust resistor is tied to the drive pin instead of ground it works in constant off time mode. In this mode the frequency varies as the line and load vary to maintain a constant current output.

skeeterb

That circuit is a whole lot simpler than most PWMs that are found out there on the net. I may use that if I do build my Hydrogen on Demand system eventually.

__________________
We are the BORG. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service US. RESISTANCE IS FUTILE

skeeterb

Using the previously attached Schematic, what could be used to control the duty cycle of that circuit, w/o using a PIC Microcontroller?

__________________
We are the BORG. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service US. RESISTANCE IS FUTILE

Ubergeek63

Are you asking about the 555 circuit or the HV9910?