Bench Power Supply Settings

[garry_1183]

Relatively new to making circuits, thinking of getting a bench power supply.

Would like some advice on recommended current settings, no doubt this would depend on the circuit, but is it common practice to calculate wattage of a circuit before dialling in a safe amperage, or is there a base line minimum value?

I'm not very familiar with the theory side of electronics, so any advice, links to articles or YouTube channels would be appreciated.

 

[GAStan]

What do you plan to make that you will use the power supply for? Just pedals? I just got a 30volt 10amp supply off Amazon that works well for me for about $40.

Ohm's Law and Watts' Law are a good place to start for theory, Google is your friend

 

[BuddytheReow]

Just about all pedals, at least the ones offered here, take less than an amp

 

[pricklyrobot]

Looking at a couple of random Boss and EHX power supplies I have lying around, 200mA output seems pretty common.

Maybe use that as a starting point, if you don’t know how much your circuit is supposed to draw.

Then do this to set your current limit:

• Turn voltage and current knobs down to zero

• Jumper a wire between positive and negative terminals

• Turn the voltage knob up a 1/4 turn

• Slowly turn up the current knob until you reach your desired current limit (e.g. 200 mA). The voltage should stay near zero

• Turn off the supply and remove the jumper

• Turn on the supply and increase the voltage until you reach your desired level (9V, or whatever)

• Turn off the supply and attach your circuit.

 

[jwin615]

Get a supply with CC/CV settings. Most decent supplies will do this.
You'll keep it in CV, which is constant voltage. The supply will feed whatever current is demanded and maintain the voltage setting.
You can't really feed excess current into a good proper working solid state circuit.
If you see an abnormal current spike, then you know you have an issue/short.
Just like you can power a 10mA fuzz with a 200mA supply without issue.

 

[garry_1183]

Get a supply with CC/CV settings. Most decent supplies will do this.
You'll keep it in CV, which is constant voltage. The supply will feed whatever current is demanded and maintain the voltage setting.
You can't really feed excess current into a good proper working solid state circuit.
If you see an abnormal current spike, then you know you have an issue/short.
Just like you can power a 10mA fuzz with a 200mA supply without issue.

I was hoping this was the case.

The Gigrig power supply I use on my pedal board has 5A available, but the pedals only draw what they need.
I was concerned a bench power supply would force whatever current was set. I'm guessing they do in CC mode?

I'll stick to CV, unless I know the current draw of the circuit.

 

[pricklyrobot]

Constant current is for devices that you want to operate at a fixed amperage but that may have fluctuating voltage. It doesn’t “force” a current, it just keeps the current steady while allowing the voltage to fluctuate as demanded by the load. LED lighting is a common example.

Pedals, barring some really esoteric design I’m not aware of, are always going to be constant voltage. Voltage stays the same, amperage may fluctuate based on pedal settings and such.

You may want to adjust the current knob for limiting in some situations. But the circuit is only ever going to pull the current it’s designed to pull regardless of what’s available. Just like the plug on your wall can provide up to 20A, but most things you plug in will only pull a fraction of that.

Current limiting is a good thing to do if you’re breadboarding new/modified/experimental circuits.

If you’re just using your bench supply to test confirmed good designs before you box them, it’s probably less of a concern.

 

[garry_1183]

Constant current is for devices that you want to operate at a fixed amperage but that may have fluctuating voltage. It doesn’t “force” a current, it just keeps the current steady while allowing the voltage to fluctuate as demanded by the load. LED lighting is a common example.

Pedals, barring some really esoteric design I’m not aware of, are always going to be constant voltage. Voltage stays the same, amperage may fluctuate based on pedal settings and such.

You may want to adjust the current knob for limiting in some situations. But the circuit is only ever going to pull the current it’s designed to pull regardless of what’s available. Just like the plug on your wall can provide up to 20A, but most things you plug in will only pull a fraction of that.

Current limiting is a good thing to do if you’re breadboarding new/modified/experimental circuits.

If you’re just using your bench supply to test confirmed good designs before you box them, it’s probably less of a concern.

Ah, okay. That makes sense.

So when calculating wattage, it wouldn't be voltage x the amps settings on the power supply, but voltage x current draw of the circuit?

 

[temol]

What kind of devices do you plan to power with this power supply? What range of voltages and currents? A few mA? A few amps? 9V? 30V? Analog pedals don't draw much current, and it may turn out that at 9V and 10mA you don't need such gadgets at all.

 

[garry_1183]

I don't know yet how far I'll go.

I've only just started with basic circuits, and bread boarded a couple of overdrive circuits.

I've no previous background in electronics so still very much a beginner.

Not got a good grasp of the laws and equations yet.

Initially I suspect I'll mostly be making 9v pedals, as I have with 9v batteries, but I'd like to make some 12v VCO's, VCA's and VCF's.