boost converter fun

schreef in bericht news: snipped-for-privacy@a75g2000cwd.googlegroups.com...

The theory is described in wikipedia and I can't do better. Switching frequency depends largely on the type of the inductor. For the coil of an

But... Compare the schematic of wiki and PMW controller carefully, especially the triple coil, switch and diode. You'll have to see if you ever want to do electronics.

petrus bitbyter

Hi, Michael. Do you still have the diode connected? That will keep your inductor voltage from going more than 0.7V higher than your power supply.

Actually, the diode is doing something valuable -- protecting the transistor. If you've got a standard TIP31, its VCE(max) is only 40V

-- you will probably end up smoking the transistor. If you would like to do something like this, try the TIP31C -- it will do 100V.

Cheers Chris

Yes, I do have an NTE587 (I think) it was still connected. That would explain it then... I didn't think that side would see the high voltages... hmm...

I've actually got the IRF530 there... good to 100V I think. But now I don't want to fry my 555...

Yep, it's pretty obvious that this isn't my main area of expertise. Just found a couple of coils in the garage, and thought, hmm... maybe I can make a boost converter.

I'll have to dig out my old electronics book... I remember the part about V = L dI/dT, but determining L and deltaI would be a bit tough for me... (any suggestions?)

Michael

Boost converters aren't that difficult to make even with some pretty unusual parts (like motor windings for inductors).

Typically they use very small inductors and very high switching frequencies. The frequency goes up as the amount of energy stored in the inductor goes down. 100 HZ is reasonable for using a motor or transformer as the inductor since that represents a large inductance.

A motor might be less than ideal if you are talking about a shaded pole or other induction motor - They have shorted turns to simulate a rotating filed to start the motor turning.

The 555 cost you 20 cents? The transistor probably costs $1 - worry about blowing the transistor - it takes the brunt of the abuse and costs more.

DIODES - pay attention to your diodes in switchers. ordinary rectifiers are nearly useless in some switching supply applications. Rectifier diodes like the 1N4000 series are too slow - once they start conducting they conduct in the reverse direction for a time before they turn off - square waves and fast rise time pulses require high speed rectifiers. With ordinary rectifiers some of your power will be wasted as heat or the switching transistor will self-destruct due to a slow diode - or the diode will short and take out other parts.

If you only need tens of milliamps at less than 100 V a fast signal diode like the 1N4148 will work - great for little battery projects like LED boosters to work 3.5 V leds with 1.5 volt supplies. Lots of stuff on the web for that and it is an inexpensive way to learn about switchers.

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

You were absolutely right. I removed the diode from the PWM circuit, and got around 50V before I chickened out and cut the power. I also removed the two capacitors from the PWM circuit; they're only rated at about 10V or so.

Hooked up my 5W night light, and the New Improved boost converter topped out at around 35V. Enough to make the night light glow slightly. This was at about 80% duty cycle.

Fun stuff.

Thanks everyone,

Michael