1. Home
  2. Electronics Design
  3. Power Supply Quiz

Power Supply Quiz

Got a short quiz for anyone willing to give it a go.

These questions are for a standard power supply voltage doubler circuit. Although this quiz applies to any normal component values (except very large capacitors or transformers with large series resistance), let's say the transformer voltage is 10VAC RMS, .2 ohm secondary resistance, 2 capacitors of 1000uF each, a 50 ohm load, and

1N4004 diodes. Assume the power supply is switched on at the zero-crossing of the power line, and the line voltage and the load do not change over time.

  1. Does the maximum surge current from the transformer occur on the first half-cycle of the line?

  2. How much more (or less) is the surge current on the 2nd half-cycle compared to the first? You can say the same, a little, or a lot. Have to include if it's more or less though.

  1. What about the surge current in the 3rd half-cycle? How does it relate to the other cycles?

  2. How many half-cycles does it take for the power supply generate its maximum DC voltage?
Reply to
Wingsy
Loading thread data ...

Ok, did it! Now, give us the answers...

Reply to
GM

C'mon, give it a try.

I can tell ya, if someone had sprung this on me a week ago, I would have gotten a zero on this quiz.

-Wingsy

Reply to
Wingsy

Which doubler? Full wave will have equal inrush currents on the first two half-cycles. Half wave will draw about half the current on the second half-cycle.

Tim

-- Deep Friar: a very philosophical monk. Website:

formatting link

Reply to
Tim Williams

Depends on other factors too. The secondary resistance doesn't tell the whole story either. Need to know the entire ESR of the xformer, what part of the AC cycle it was last turned "off" at, to know if it's going to saturate when it turns on and the L/R time constants etc...

This is not as simple of a question, as you've obviously found out.

boB

Reply to
boB

No.

A lot more.

A lot more than the first, more than on the second and slightly less than on subsequent half-cycles.

Infinite. Theoretically, the voltage will keep on increasing in a parabolic curve, never quite attaining a steady level.

P.S.: These answers are not based on text book theory, but on my understanding of how things work. Have the dunce cap ready. :-)

Reply to
pawihte

Full wave.

Reply to
Wingsy

If you need a figure for that, use 51 ohms for the primary resistance.

Oh, the questions are kinda simple. It's the answers that will make your forehead wrinkle up.

I'll post the answers this evening when I have time. I'll give a link for a Power Supply Simulator app as well (free).

Reply to
Wingsy

Got one and a half right. At least you're the only one who has the guts to publish your answers.

Reply to
Wingsy

"Wingsy"

** Where is this "surge current" measurement taken ??

In the primary or the secondary of the tranny ???

Very BAD of you to leave this CRUCIAL point ambiguous - especially after folk had queried you on it.

..... Phil

Reply to
Phil Allison

You are the only one who appears to be confused on this.

"from the transformer" means... uh.... "from the transformer". Since transformers usually have current put into the primary and taken out of the secondary, it surprises me that you have a question about this. So, to answer your question anyway, the current measurement is taken at the transformer secondary. But wouldn't the surge current in the primary occur at the same time as the surge current in the secondary?

Reply to
Wingsy

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.