boost fets ..... is there an afterlife

[12AX7]

Hey Oztules!

I see your up to post #65!

I was "satisfied" awhile back...

now..   I think you've found some yourself!

enjoy!

[Flux]

Sorry that should be 25NP. that is the hall sensor that needs 5v and output sits at 1.5v with no primary current.

Not sure what you can get on the island but there are other LEM beasts, Allegro do something and Honeywell do the Lohet series ct's.

I am not sure how you use a current mode controller for this. I think the pwm feature of these is a secondary thing as a result of the current control. My thing is just a pwm controller. I am not familiar with the 494 but I seem to remember it is rather similar to the 3524 and will need a mosfet driver stage and to get more than 50% duty you may need to add the outputs, but 50% is about enough.

Flux

[oztules]

The closest thing on the island to a hall effect device is probably the silicon up at Killecrankie (quartz  in the granite).... so it'll have to be imported.

I'm thinking that the i sense in the current mode can be turned on and just use the error amp to do the pwm much the same as the voltage mode devices. Failing that, the tl494 with its outputs joined gets upwards of 95% and I am already using it in that manner with totem pole transistors to drive the fets.

I have seen articles on using current modes in voltage mode, now i will have to dig them up.

.............oztules

[dinges]

Thanks for all the info, Oz & Amanda.

I will first modify for voltage control; I aim for 5-18V. (thus will need to change some elco's that are rated only for 16V).

Will modify overvoltage-threshold to 18V (in the last few cases, it was just a matter of changing a zener diode)

And if all that works, I'll modify a 2nd one and in that one try to employ current control.

As you see, baby steps

And yes, I have always safety glasses with me. Only put them on when I think they're really needed (like with this PSU). Usually they're sitting in my breast pocket though... :/  (like two weeks ago, when two 2"x1"x.5" Neos banged together. Shrapnel flying in all directions).

Again, thanks for your troubles of explaining all this.

Peter.

[oztules]

I have seen how nicely you finish your projects, we want pics and diary of this.

Personally, I prefer do the current mod first once done it makes the supply pretty tough plus we do things upside down here.

best wishes............oztules

[oztules]

Oh dear me Flux,

For the first time so far, I ran this boost without a battery on the load side...... almost instant destruction. A quick rebuild and ....same thing. rebuild with a batt load, and no problems clean all the way up to 300w.

Is this normal for this topology.  How much resistance across  the output  to get stability.

Do you have any ideas here?

...................oztules

[Flux]

I am not sure what you have got at the moment. Without voltage regulation it is not going to work without a battery load.

Most switch mode supplies do need a minimum load to work properly. To work as a power supply you will need a significant size electrolytic on the output.

Sorry I haven't done much with high power stand alone power supplies, most of my work has been with boosting an alternator into a battery. I have no form of voltage regulation and wouldn't really expect it to work without the battery as a voltage clamp.

Without some form of voltage clamp the inductor volts will go sky high and even with voltage regulation you will need sufficient capacitance to clamp the first few cycles to a safe voltage before the voltage loop can phase back.

You will almost certainly need some form of diode, capacitor, resistor snubbers to catch the initial spike.

Flux