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buck converter modules - current limiters

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Wp100

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Hi,

A lot of the far east buck converters have adjustable current limits, but not having used one, wanted to know what happens if say the current is set to 1 amp, and then the load demands more than 1amp, eg a short, does the converter just continue to supply 1 amp or does it cut the power off all together ?

thanks
 

Tony Stewart

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Most Helpful Member
Without specs all you can do is look at the bad photo and and datasheet of the part number and hope it has a hiccup shutdown and retry. Although on my Bose amp I recently discovered after playing Midi from my Yamaha digital piano it has better bass and loud but it shutdown the radio until I unplugged it and that reset of the OCP.
 

MrAl

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Hi,

Some of them will switch to current regulation so that it will put out 1 amp but the voltage will be reduced. So say it is putting out 5v at 0.5 amp which would be a load resistance of 10 ohms, then the load changes to 5 ohms, then it would put out 5v at 1 amp, but then if the load changed to 4 ohms (down from 5 ohms) then the output will still be 1 amp but the voltage would drop to 4v, and if the load again changed to 3 ohms, then it would put out 3v at 1 amp. That's if it is the type that switches to current regulation.
But yes, it depends highly on who makes it and what model number the buck circuit is as some will do this and some will just shut down. So you really have to look at the specs for your actual board.
 

Wp100

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Just that many such units give only the most basic specs, hence my question; thought it might be a standard method, but seems not.

Thanks.
 

crutschow

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I would think that most units just reduce the voltage and limit the current to the rated value since other types of current limits tend to require more complex circuitry, but I have no direct knowledge of this.
 

dr pepper

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I tried shorting a imported regulator module to see if it would current limit, it didnt it blew up.
The idea is to reduce the voltage to limit the current to the setpoint, if you take the mick and short the o/p though on the cheaper ones bad things can happen.
If the controller ic is voltage mode then this makes it more likely to go bang, current mode is less likely.
 

ChrisP58

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If the product is described as having and adjustable current limit, then it probably has extra circuitry to control the current, as opposed to just relying on an over current limit that might be in the PWM controller.

The biggest market for controlled current buck converters is for battery charging. When the battery is discharged, it's terminal voltage is low, and a low impedance constant voltage supply will often shutdown or fail because the battery will take as much current as it can if the supply voltage is higher than the state-of-charge battery voltage is. For that reason, you need a supply that has both a current limit, and a voltage limit.

For example, a 1 amp charger single LiIon cell will deliver a controlled 1 amp of current into the cell as the voltage rises from 3 volts to 4.2 Volts. At that point, the voltage will stay at 4.2 Volts as the current tapers off to near zero.
 

spec

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I have never come across a cheap switching regulator that cuts out on current limit. The vast majority just go into current limit either dictated either by the energy storage in the switching inductor, or specific current monitoring which is provided on some SMPS chips anyway. You can get SMPS with fold back (supply a lower voltage on a short circuit) but that is normally specified in the advert description.

Battery chargers are different again and have accurate voltages and currents to suit the various battery chemistries, apart from lead acid batteries, that is, where anything goes, it seems.

spec
 
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