13.8v (or 15V), 8A switching power supply

[mvs sarma]

please see this product and I feel it is rather cheap . One can verywell manage with it unless one has to make it by himself.

**broken link removed**

 

[BengBear]

Hi Sarma,
I live in Singapore. I had some experience with China made switching power supply, which cost about S$100, US$77. It say adjustable 0 to 24Vdc and 10Amp. In reality, adjustable to 16Vdc and 4.5Amp.

Thank you for following this thread closely. Just want to be assured, did you know of anyone who had use this brand. Please let me know their experience.

Meanwhile, Hero base on the attached Planar information appreciate any circuit and IC recommendation.

 

[mvs sarma]

Hi Sarma,
I live in Singapore. I had some experience with China made switching power supply, which cost about S$100, US$77. It say adjustable 0 to 24Vdc and 10Amp. In reality, adjustable to 16Vdc and 4.5Amp.

Thank you for following this thread closely. Just want to be assured, did you know of anyone who had use this brand. Please let me know their experience.

Meanwhile, Hero base on the attached Planar information appreciate any circuit and IC recommendation.

Generally a psu with adjustable output will be costly. So if you need a fixed voltage, better go for fixed smps. As e-bay has quoted below 20 bucks, there is no need to pay more than 25$. i got the info only on net and never I used the device.

 

[neon]

My Idea Is To First Use A Hi Voltage Preregulator For 180v To Insure That The Power Will Not Go Away When It Dips And Bounce. Then Use Low Voltages Pwm To Get The Current

 

[BengBear]

ok, this sound interesting. please post schematic of the circuit.

 

[petrv]

Off-line switched PSUs can be designed as "universal" - working in the 85V - 265V range. That would make the preregulator unnecessary.

 

[mvs sarma]

My Idea Is To First Use A Hi Voltage Preregulator For 180v To Insure That The Power Will Not Go Away When It Dips And Bounce. Then Use Low Voltages Pwm To Get The Current

every stage counts on your pocket and also on power efficiency. It is always better to work a one time solution. Unless one is going for a project, i still feel the site indicated by me sells a psu very cheap.

 

[Ubergeek63]

Perhaps your concept is right, if you source the L4970A, perhaps you can complete it. You may have to use a high power bridge rated 20 amps to safely deliver 8 amps.

Please see this pdf
https://www.electro-tech-online.com/custompdfs/2008/05/powsupply-1.pdf

even drawing 500W from 220VAC is only about 2.25A so a 5A bridge would be fine.

 

[mvs sarma]

even drawing 500W from 220VAC is only about 2.25A so a 5A bridge would be fine.

My suggestion was with specific reference to L4970A chip and the schematic there on provided by the OP. There after the OP wanted to use Planar transformers-- i was confused with low height CRGO core transformers --some of them I saw in light dimmers( Really sleek and wide.)

 

[Hero999]

even drawing 500W from 220VAC is only about 2.25A so a 5A bridge would be fine.

Although he'd need to use some inrush current limiting to avoid destroying it.

 

[Ubergeek63]

Actually diodes are quite robust, it is the filter caps that need protecting. Case in point: a 3A rectifier shunting a 600A lightning strike around a PFC circuit.

 

[Ubergeek63]

And, for something more concrete, one that we use at work, https://www.electro-tech-online.com/custompdfs/2008/05/ds21221.pdf is a 25A bridge that is rated for a 350A half cycle sine.

In other words you generally do not have to worry till you get well beyond 10X rated current. Generally your system resistance is enough to keep you under that limit.

 

[Hero999]

Of course you are right but you still need to check the surge rating.

For a small 1.5A rectifier used in a little linear supply, this isn't normally a problem. A 1.5A rectifier can hapilly stand 25A and the internal resistance of the transformer will limit it to a safe level.

However, when you're running the circuit directly from the mains, it's a different story.

What's the peak current through the rectifier?

How many cycles does it take for it to charge?

If the resistance of the mains is about 0.5hm: and the peak voltage is 325V, the peak current would be 650A so you think your rectifier would be toast? Suppose your capacitor is 1000:mu:F, then the surge would decay rapidly to within 63% within 500:mu:s so the capacitor will be as good as fully charged within 5ms.

So as we've established a 25A rectifier will be fine but what about the 5A rectifier you initially suggested? Somehow I think it'll be toast.

 

[BengBear]

Wonder if there is any Planar Transformer of Pulse Technitrol match the switching transformer spec detail in attachment.

 

[BengBear]

difficulty buying or finding equivalent for following:
PH4840, Si7370 and PH21NQ15
BCX55

from Fig 16, DC to DC converter circuit, of page 21.

Anyone can review and offer solutions.

 

[Ubergeek63]

If the resistance of the mains is about 0.5hm: and the peak voltage is 325V, the peak current would be 650A so you think your rectifier would be toast? Suppose your capacitor is 1000:mu:F, then the surge would decay rapidly to within 63% within 500:mu:s so the capacitor will be as good as fully charged within 5ms.

So as we've established a 25A rectifier will be fine but what about the 5A rectifier you initially suggested? Somehow I think it'll be toast.

https://www.electro-tech-online.com/custompdfs/2008/05/s5a.pdf
A 5A diode is good for 100A peak 8.3mS surge on top of the full load current.

That makes for an RMS of 70A for 8.3mS at 1.5V or 106W.

While not exact, it should be able to take a single pulse of 650A for 8.3*106/650A/1.8V=0.75mS.

Looking at the diode's I/V curve and projected to 650A gives approx 1.8V, the ratio of the wattages tells you how long it takes 650A to heat the crystal the same amount as the 70A RMS pulse rating does.

 

[Ubergeek63]

Even by your assumption (0.5hm: source ideal 1000:mu:F capacitor) the current will be down to 300A in 0.5mS. A typical 400V 1000:mu:F cap will add 0.25hm: to the 0.5hm: line knocking it down to 433A.

That brings us to 8.3*106/(433*1.8)=1.1mS ... you can add to this the exponential decay of the capacitor current to get an even better idea of the peak inrush current the diode will handle since this is a quick square pulse approximation.

 

[Hero999]

What mains voltage are you using in you calculations? I used 230VAC.

You have point about the ESR of the capacitor reducing the current, then there's any inductance in the line which should also help.

 

[BengBear]

I think it is ok to assume that input current to a DC to DC converter (having 40Vdc input and output 13Vdc 10Amp) is less than 0.5Amp.

Appreciate comments, yes?

 

[Nigel Goodwin]

I think it is ok to assume that input current to a DC to DC converter (having 40Vdc input and output 13Vdc 10Amp) is less than 0.5Amp.

Appreciate comments, yes?

Hopefully you meant 240V and not 40V?.