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Maker Pro

pwm for a boost converter

C1 smaller (than shown), and the pot smaller (maybe 10k).

500pF is a little on the low side for a 555 but will still work. I think
20kHz is about right for that (or 0.005uF with a 10k pot).

I heartily recommend an UC3844 or similar chip for doing a boost converter.
The current protection will keep your transistor from exploding, a notable
advantage.

I was messing around with a BS boost circuit (two comparators and an op-amp,
plus the obvious hardware) just tonight and popped two power transistors.
:( Car batteries can sink a lot of current...

Tim

Ditto. Those 555 circuits are like using a crescent wrench instead of
a socket. Eh, maybe pliers instead of a socket.
 
T

Tim Williams

C1 smaller (than shown), and the pot smaller (maybe 10k).

500pF is a little on the low side for a 555 but will still work. I think
20kHz is about right for that (or 0.005uF with a 10k pot).

I heartily recommend an UC3844 or similar chip for doing a boost converter.
The current protection will keep your transistor from exploding, a notable
advantage.

I was messing around with a BS boost circuit (two comparators and an op-amp,
plus the obvious hardware) just tonight and popped two power transistors.
:( Car batteries can sink a lot of current...

Tim
 
R

Rich Grise

^^^^^^^^^^^^^^^
AKA "adjustable nut-fucker"

When some newbie would show up in our shop to ask to borrow a
crescent wrench, we'd ask, "Metric or Standard?" :)

Cheers!
Rich
 
H

Homer J Simpson

When some newbie would show up in our shop to ask to borrow a
crescent wrench, we'd ask, "Metric or Standard?" :)

Left or right handed?
 
T

Tim Williams

Heh, I realize that those are useless distinctions which can actually
apply -- the only chiral part is the adjustment screw, while the wrench
length is measured in perhaps 8" or 200mm.

Now, a bucket of vacuum...

Tim
 
J

James Arthur

Re: this schematic:http://www.cpemma.co.uk/555pwm.html

If I change C1 to 500 pF, would I get a 20 kHz PWM frequency?

Would any other modifications be necessary to achieve 20 kHz?

I'm trying to build a boost converter, and I'd like to use a variation
on this circuit to perform the switching.

Thanks,

Michael

That's not a very good general-purpose power supply, as others have
noted. Why not use one from my pal Bill Bowden?

http://ourworld.compuserve.com/homepages/Bill_Bowden/page4.htm#ps5.gif

Be sure and use a suitable (fast) rectifier, like a 1n5819 schottky,
or a fast-recovery type.

Best,
James Arthur
 
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