Often the only internal load is the resistive divider for the regulator loop feedback.
I have some. They drop very slowly when there isn't much load on the output.
A synchronous buck architecture should work quite well if you need to slew fast. I've used that on a driver that had to modulate a hard capacitive load at several kHz and above 100V.
It's always made more sense in power test gear, if you can afford it. It's a penny-pinching part of the industry.
In the loading case, you don't end up contributing much to the line, you just draw net losses from processing, so no complications for hydro.
For PV or other energy sources - it's a negotiation that's dependent on local supplier and contracted regs.
RL
Capacitors and inductors are as 'short' as their reactance allows.
Just don't be surprised when it happens - that's all I'm saying.
RL
That goes without saying for linears. SMPAs are increasingly low-cap as the conversion frequencies rise. Smaller switching amps - think mp3 portables - don't bother filtering anything, they juat figure the load will do it for them.
The $2 regulators from offshore are a role of the dice (or carefull visual inspection), whether an output filter is there, or not. Some of the cheapest even expect a common + rail.
I've seen unfiltered high power stuff that lets a lossy LF isolation transformer do the job, but you shouldn't be able to smell (or hear) a power supply in operation, if it's properly designed.
Another instance of 'Why Can't I Do That'.
You WERE saying 'good', so I expect you're in a different ball park.
RL
One of he big linear HP supplies has a few thousand uF at its output, and a barrier strip that allows another 5 or 10K more, internal, to be strapped in.
Customers might whine if they ask for 10 volts and see 30. Amd that may be mostly held up by their capacitive load.
I'm doing some multichannel non-isolated supplies that will be sync buck, using multiple TI DRV8962 chips.
One problem is that a sync buck can become a boost in the wrong direction, and start charging my +48 supply. If it hits, say, 55 volts, I'll disable the switcher chips, and the outputs can hang. I need to discharge the outputs. I'm thinking about 20 mA of depletion fet per channel.
Come on guys, quit pontificating and start measuring.
At this stage in the process, you seem to have some odd constraints. Why the specific h-bridge driver? Why non-isolated?
Sylvia.
You might consider overvoltage protection or a (switched ?) internal minimum load.There's usuaally some point in the control loop that's a good indicator of a pull-down requirement. A single ovp or autoload on the input looks likely to serve all of your many sync-bucks.
RL
There are certain configurations of self-driven sync rectifier - gate drive supplied by actual transformer terminals being rectified - that will self-oscillate with no input, when output power is present. This pumps output power back through the isolation barrier and can be a bitch when parallel redundancy is attempted without orring diodes.
- so your situation is not only present in actively driven sync rectifiers.
Reversible power transfer, however, is not always a curse. You just have to be aware of the possibility and make sure that it's not actually unsafe to your hardware.
It can be usefull.
RL
What I suggested is that a few people grab their bench power supplies and see what sort of output capacitance they have.
The simplest way is to crank the voltage up and short the ouput and see how much it sparks. Or measure the capacitance, even.
That quad TI driver is cheap and available and seems to have good protections. TI makes good stuff and keeps it in production approximately forever.
Non-isolated because that's simple and gets more channels on a small board. The launch customer says that power supplies don't usually need to be grounded because everything is grounded on an airplane.
An MOV on the bulk supply could limit the reverse-pump excursion until the software can notice and shut things down.
MOVs can gobble a lot of joules, but their clipping is very soggy.
MOVs are usually cumulative. They can take a certain amount of dissipation over their lifetime and then *PHUT* ... POOOF. Like a bank account that runs dry.
What kills MOVs? Integrated joules? Time-temperature?
I don't expect a lot of joules per event. Just enough energy to keep my supply voltage down until a slowish ADC and the software can shut the buck switchers down. 15 milliseconds max, maybe.
I am thinking that nobody here actually has a power supply.
I think it's integrated joules per cubic centimeter of the MOV material. This is discussed in the literature on MOVs for protecting line-powered equipment from pulse overvoltages, such as from nearby lightning strikes.
Joe Gwinn
Makes sense. It looks like most MOV appnotes assume that it's across an AC line, with kilo-amps available. Or lightning bolts.
I'll get a few and test them at much lower loads.
For smaller MOVs, I think that the data sheet specifies capacity in Joules. I bet this is the max integrated dose, not the pre-event limit. Well, the one-event limit as well.
Joe Gwinn
That's probably a single-shot rating, such as to limit the peak temperature. So that can be done many times, if it cools off between shots.
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