Book on Switching Power Supplies

[lowell]

Amazon.com: Switching Power Supply Design (9780070522367): Abraham Pressman: Books

Anyone read this? Or maybe have a suggestion on some reading material for the subject? I'm pretty good w/ tube electronics and understand transistor operation fairly well. I don't want a book that will be way over my head here.

[Jazz P Bass]

Switch Mode Power Supplies

Hi Lowell.
Are you looking to learn or design?
I have (2) pdf files I will atach on SMPS & power supplies in general.
Personally, I think the design book will go a little too deep.

[lowell]

Ok right on, thanks JPB, I'll check out those files.

[g1]

Some general info. and books listed under reference section here:
Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies

[Jazz P Bass]

SMPS

Lowell
Here is a pdf I have that explains how a real simple SMPS works.

[lowell]

JPB, cool I understand the flow and explanation of that circuit. Now, how much current can the Vout supply? Also, does the 555 chip do the voltage amplification? If so how?

Regarding the Buck regulator, why use this? Is it simply because of the physical size in that it may be smaller? I ask because why not just use a step down transformer and rectifier, because Vin is DC? And if that's the reasoning, why not just a zener or basic regulator circuit?

"Since the energy stored in the
inductor is equal to L x I x 1⁄2, the PWM (pulse width modulator) IC can increase Vo by
increasing its own on-time to increase the peak inductor
current before switching."

Not sure I get this. Say Vin is 9v. How does the PWM boost Vin? I understand that the shorter time that Ton is, that it will increase the average voltage, but the PWM must have a higher PEAK voltage to boost the 9v... right?

[Jazz P Bass]

SMPS

The 555 is being used to "switch" the power transistor on & off.
There is no amplification.
Just really fast switching.

A Buck is a Buck. The different configurations all have there uses.

As to the last part: the PMW is, again. switching the power transistor on & off. By varying the on time, the transformers are conducting longer.

Maybe reread the Nixie pdf.

Here is a link from National Semi on SMPS.
Link:http://www.national.com/appinfo/power/files/f5.pdf

Lastly, the Nixie is good for about 10ma's before the output voltage suffers.

[defaced]

A user named Frequency Central uses SMPS for a small tube amp he sells. There's a thread about SMPS design on one of the stomp box forums, The MAX1771 SMPS Development Thread
He's traditionally used 555s, but for one reason or another (I haven't been following it closely) wants to play with this chip.

He's written alot about the topic so it may be worth digging a little.

[Enzo]

Lowell, it is the inductor that gooses the voltage up high.

When current flows through an inductor, it wants to keep that current flowing. If you then interrupt the current, the inductor field tries to ramp up the voltage to make the current continue.

When Q1 is on, the inductor is placed across the +9v supply, and it is "charged" with the current flowing through it. When Q1 turns off, L1 tries to keep the current flowing, and the result flows through the only remaining path, D1 into C4, which charges from that.

Regarding the Buck regulator, why use this? Is it simply because of the physical size in that it may be smaller? I ask because why not just use a step down transformer and rectifier, because Vin is DC? And if that's the reasoning, why not just a zener or basic regulator circuit?

The whole point of switchers is their far higher efficiency and lower cost. Zeners throw away a lot of power as waste heat. If you are plugging a wall wart into the AC mains for a littel effect pedal, then fine, but when batteries are used, then power waste means shorter battery life.

[lowell]

Ok so the inductor boosts the voltage as it attempts to maintain the current through it. In the case of a Yamaha SPX90 I'm repairing, it's always gonna be plugged into a mains outlet so no battery drainage there. I'm guessing that the SMPS is smaller than any traditional transformer coupled supply? I'm gonna read through those pdfs some more too try and clear this all up in my noggin.

So the key equations are:
Vo = Vin (T/(T – t(on)))
(where T=time right?)

Also, L x I x 1⁄2 is the energy stored in the inductor. So a larger L or longer t(on) for more current increases the inductor's stored energy?