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But it's regulated! :expressionless: There shouldn't be an unloaded voltage.

That's nice though -- I've been thinking more and more about getting building a programmable bench supply. In the meantime, I usually put in the smallest fuse that should do the job, plug something in to a power strip, and hide behind the cat as I power it up.

I like that because of the fixed 5 and 12, over and above whatever you choose on the main output.

SirNickity:
But it's regulated! :expressionless: There shouldn't be an unloaded voltage.

That's nice though -- I've been thinking more and more about getting building a programmable bench supply. In the meantime, I usually put in the smallest fuse that should do the job, plug something in to a power strip, and hide behind the cat as I power it up.

But doesn't that only work up to nine times? How many cats have you used up?

Lefty

I try to wear-level between the two, and thankfully their sacrifices have been minimal. :wink:

Jantje:
is it me or ....
The cover says 18V and the LCD says 19.0V :fearful:

It must be (probably) a small reserve, the power supply was photographed without a load. With the load will show probably less than 19V. But a little more than 18V is no harm.

JimboZA:
I like that because of the fixed 5 and 12, over and above whatever you choose on the main output.

I like too. But only 0.5A for branch. 5V/0.5 A is usually enough, but 12V/0.5A is insufficient, for example, for LED strips testing.

K5CZ:

JimboZA:
I like that because of the fixed 5 and 12, over and above whatever you choose on the main output.

I like too. But only 0.5A for branch. 5V/0.5 A is usually enough, but 12V/0.5A is insufficient, for example, for LED strips testing.

Well that's when you dial in the 0-18vdc @ 5 Amps. Bet that dog barks. :wink:

K5CZ:
It must be (probably) a small reserve, the power supply was photographed without a load. With the load will show probably less than 19V. But a little more than 18V is no harm.

SirNickity:
But it's regulated! :expressionless: There shouldn't be an unloaded voltage.

So we have a dispute here. One says it it s a regulated power supply, the other says it is not. :astonished:

(Hint: If it is regulated and able to supply full load at full voltage - implies switchmode - then the ability to somewhat exceed the nominal rated voltage is not at all dependent on load.)

Sorted

Subtle!

Trolling... as small kids :slight_smile:

So, here is the factory page:
http://www.manson.com.hk/products/detail/18

And chapter IX. Specification says:

Over Voltage Protection (Main Output): 18~22% at tracking 10.1V <Vout ?19V

I have no idea what this mean, but there is an undeniable existence of value "19V" and maybe it's a relationship.

One thing to know about bench supplies like this is that they can't always supply max amps especially when using outputs as low as for example 1 vdc. A linear regulator can exceed it's maximum heat dissipation before reaching it's maximum output current rating due to the extremely large voltage drop across the regulator when set to lower output voltages.
I've seen some complex designs that lowers the unregulated voltage input to the linear regulator as one lowers the desired output voltage to keep within heat dissipation rating. Only a schematic drawing would tell if there is anything like that used in this unit, but perhaps the owners manual covers the issue?

Back in the 80s we used H.P. bench supplies like this (except metered not digital displays) that would cost around $1,500 or better depending on options. They were bullet proof quality and were hard for even a beginner to damage.

Lefty

A 5A linear supply? Wow, I wouldn't have guessed that.

5A linear, aka boat anchor as the EE's who taught me "go for smoke" called them at fests.

I've been wondering if something would work. I have 9V supplies that if I put a 7.5V zener and a good bit of resistor across +9 and GND, would I get 7.5V to a 5V regulator without wasting much power? I am guessing that the resistor would share the heat of 9V down to 5V with the regulator but how to figure the resistor value?

Does that even make sense?

Using a resistor in series with a Zener is a common way to get a voltage reference, but it's of limited value as a regulator. Basically the current draw has to be exceedingly small, because as you pull variable current from the supply, there will be a corresponding voltage drop. If you follow this with a traditional linear regulator, sourced from the junction between R1 and D1, the regulator will drop the remaining voltage. This could be anywhere from the entire voltage difference (at no load) to being already well below the desired regulated voltage (at heavy loads). If you calculate the max allowable current draw and size the resistor so this load corresponds to the point where its voltage drop results in a perfect Vin for the linear regulator, you can probably make it work, but it's a kludge.

In addition to being dependent on current, using a resistor is not at all an efficient way to drop voltage -- it becomes wasted heat. However, it's essentially how all linear regulators work (except the resistance is variable depending on the load) and also what makes linear regulators inherently inefficient.

None of that really takes the Zener into much consideration. For that, you have competing goals: Keep the resistance high to avoid dumping tons of current through the Zener, which would overheat it and burn it out; and keep the resistance low so you can draw current from the PSU without simultaneously dropping all available voltage through the resistor. There's a fairly small window where you can satisfy both criteria.

Your line of thinking is how to reduce the heat load on one regulator, correct?. The simple solution to this is to spread that load among other devices. One such way is to use a regulator as a controller, and have the load pass through a heftier transistor (and/or parallel transistors). You can also pre-regulate the voltage so the drop is shared between two or more regulators. This works, but it's usually not the best approach.

Would an LM317 get around all that? I think I have however many a dollar or two cost from where I fleshed out an order with cheap, interesting-looking parts to justify shipping... in one of my past purchases (back OT?).

No, an LM317 is still a linear regulator -- it's just designed to output an adjustable voltage. You can force a 78xx or 79xx to change their regulated voltage too, if you step outside the typical application design in the data sheet.

Many of the linear regulator datasheets do include schematics for using external transistors though. Then you're designing a linear regulator that has much in common with a Class B power amplifier, with the same flaws... namely, that Class D amps and switching regulators can be much more efficient for high-current loads, at the expense of being more complicated and not as well behaved if poorly designed or poorly matched to the load.

Air, and some RGB LEDs for my Mood Light (look meh up on Instructables)

A 99 cent, 12vdc @ 2 amp switching regulated wall transformer with 10 foot cable with standard arduino like connector at a local charity store. Can't have too many of these.

Lefty

2mm & 5mm heat shrink cable.