Are there circumstances where a power supply/brick pushes a charge pump too hard

[Mark Hammer]

A buddy on another forum has a malfunctioning pedal that uses a charge pump.  When he reported the malfunctioning pedal to the manufacturer, the manufacturer remarked that the brand of PS the fellow was using has "fried so many" of their pedals.  Not a cheap PS, though, and we know it works just fine with other pedals that don't use charge pumps..

So I ask, are there properties of some power supplies (presumably switching supplies) that interact with charge pumps that might lead the chip to fail?  For instance, might the PS "misread" the current draw and provide more current than the charge-pump can provide?

Teach me.

[iainpunk]

voltage controlled sources always deliver their chosen voltage and the load's demanded current at that voltage.
current controlled sources always deliver their chosen current and the load's demanded voltage at that current.

switching power supplies generally have a high amount of feedback, keeping the output at a strong preset voltage, and a lot of systems switching frequency is dependent of current draw. if the charge pump pulls current at certain frequency, the feedback loop of the power supply might oscillate at the same frequency.

all i know for sure is that the charge pump has been mis-designed in that case. current limiting is a big factor is designing a good charge pump, and often overlooked, with the assumption that power supplies can't give high enough spike currents to fry the transistor/chip. but switching power supplies can generally deliver relatively high current spikes if that's what the load asks for.

so that's 2 things that i can think of that might have destroyed the pedal,
- synchronous oscillations run astray
- spike currents not being averted by the charge pump's design.
anyway, i blame the designer of the pedal/charge pump, allowing the charge pump to ask for such currents. especially since most guitarists are not particularly bright, and might use sketchy-ass gear.

cheers, Iain

[slashandburn]

I'm in no position to "teach" and I'm commenting merely to follow this and learn more, but I like other Iains answer.

If a common (known working) power source breaks the product, surely the product is the problem?

[PRR]

Isn't there a charge-pump with a 10V input limit, and known to blow-up at 10.1V?

[amz-fx]

As Paul said, there are numerous charge pump chips that will die at any voltage over 10v or so. The TC7660CP or LMC7660 for example.

Couple this with the fact that unregulated power supplies will put out a voltage that can vary with the load on it. For example, if the power supply is rated at 9v and 500ma but you only load it with a 10ma distortion pedal (which is a light load), the voltage from the power supply might be 12v! Bang goes the charge pump.


regards, Jack

[danfrank]

Isn't there a charge-pump with a 10V input limit, and known to blow-up at 10.1V?

Yes, the MAX1044... It should be called the MIN1044!

[anotherjim]

I think some pedal power supplies are intended to give 9.7v. Presumably to account for drop in connections and protection diodes  - or maybe to equal a new battery. As the converter local supply cap will charge to the peak input then any supply ripple might cause it to exceed 10v. Measuring the supply with a DMM will only show you the average voltage.

However, I can't help being suspicious of the fad to "try" a pedal on higher supply which some pedalboard supplies will allow. 18v on some. Would the owner of a blown pedal necessarily admit that? Maybe a protection Zener and a self-healing fuse (which even some cheapo toys have these days)  would be worth fitting.