HELP - please explain "bench" power supply outputs

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CharlieLaub

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Joined 2007
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#1
This seems like a really "noob" question, but I can't seem to find any answers out there on the web..

So I want to get a bench top power supply to test out amplifiers that I build without having to build a new PS each time. Typically I need +V GND and -V, the usual "dual" rail power supply.

So I've been looking at benchtop power supplies, like this for instance:
Mastech 9960PS Bench Power Supply

9960.jpg


My question is whether the outputs are -V, GND, +V or something else alltogether... I can't find that exactly spelled out in any manual, although it seems like it's intuitive.

Also, any recommendations are welcome for makes and models. I would like to get something that will go up to 60V or so, +/- rails, and at least 5A (e.g. capable of 300W output) would be nice. "Single" output types are OK.

Thanks for you help...

-Charlie
 
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#3
The Mastech 9960PS is a single output power supply with the output on the black and red terminals. Either the black or red terminal can be connected to the ground terminal so you can have either a 0 to 60V or a 0 to -60V supply but not both. For a +-60V power supply you would need two of these or a dual output power supply.
 
#4
RJM1 said:
The Mastech 9960PS is a single output power supply with the output on the black and red terminals. Either the black or red terminal can be connected to the ground terminal so you can have either a 0 to 60V or a 0 to -60V supply but not both. For a +-60V power supply you would need two of these or a dual output power supply.
Click to expand...

OK, I will look at dual output supplies.

Thanks for the info!

If you have any recommendations, please let me know. Would like to have something like a 300W (200W is OK, as this seems to be a standard type) dual rail power supply for amplifier testing. Current limiting would be really nice, otherwise I could get a 10A variac and some high voltage caps and be in business in no time. At least I would be able to vary the rail voltage easily...

-Charlie
 
#5
I'm still looking for suggestions for a dual output supply, up to 60V at 5A...

This is for bench testing amplifiers, so I need to create a "+V, GND, -V" type DC voltage source like what you get from a linear power supply. According to an earlier post, I need a dual supply model, and I would tie the supplies together using the GND terminal.

I'd also like to be able to operate in a current limiting mode too.

Anyone?

-Charlie
 
#10
Ah, thanks - that's a little bit beyond my comfort level!

Well, I've had an old 50V single regulated for while. I just picked up a 0-120V, 0.5A single supply so that I can reach higher voltages, and can do the current limiting type operation, so I think I am covered there.

I'll just build a variable dual linear supply using a variac and a big transformer and caps that I have lying around. That way I only need to spend another $50!

-Charlie
 
#11
Be careful with your purchase, some bench PSUs can't deliver their rated output wattage for long periods or are derated at high voltages. We use a fair few makes at work, and one pretty useless type looks amazingly like the one in your photo. I'm not at work for a while (holiday) to check models, but I know the TTi and Thandar dual supplies we use are good.
 
#13
Many Bench Supplies have a pair of output terminals for each output of the supply.

From the pic in post1 I see three output terminals for a dual polarity supply.
I guess from this that the two supplies are connected in series, internally.

Don't buy it.
 
#14
AndrewT said:
Many Bench Supplies have a pair of output terminals for each output of the supply.

From the pic in post1 I see three output terminals for a dual polarity supply.
I guess from this that the two supplies are connected in series, internally.

Don't buy it.
Click to expand...

That's what I thought, too! What I discovered is that the three terminals on these regulated bench power supplies are:
1. GROUND
2. POSITIVE end of a floating supply
3. NEGATIVE end of a floating supply

This doesn't give you the same thing as a dual rail (+V and -V with respect to ground) power supply that is typically found audio amplifiers. The bench PS is designed this way so that it can be floated at whatever potential you desire. I found this out when I finally read a more thorough manual for a used Agilent single output PS, and by playing around with the one that I already had around (another used one I picked up for next to nothing a few months ago, but had not yet used).

So, when you want to use the supply for, let's say +15VDC, you tie the ground to the negative terminal. If you wanted a -15VDC supply, you would tie ground to the positive terminal. But you can't tie ground to the middle between positive and negative to get a symmetric DC supply. Instead, you can use a "dual tracking" supply, which has two floating outputs, the magnitude of which is the same but the sign is opposite. On one you tie positive to ground, and on the other you tie negative to ground, and this gives you the two rails at +V and -V. The magnitude of V being controlled by one knob (they "track" together).

After looking around a bit, I found that even a modest dual-tracking PS with a total power of 200W-300W at 50V is VERY EXPENSIVE! I can build a simple linear power supply (I have lots of parts already that could be used for this purpose) and just use a variac on the mains AC input to the step down transformer. It's not regulated, but is exactly the adjustable-dual-rail PS that I need to be able to test out amplifiers and so on for only the cost of a variac.

I was planning to use the constant current mode to reform capacitors - I recently bought a bunch of NOS buss type computer grade electrolytic caps that I want to "prepare" or at least check out before using. I can still do this with my regulated single supply bench PS units.

I think that this covers all my PS needs nicely.

-Charlie
 
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