with this reply :Included a cap on the 'ground' leg of the reg if there's also any resistance on the 'ground' leg (in parallel)?
You'll see in the NS Datasheet two example circuits which include a cap of 10uF between ground and the the 'ground' leg which are specifically shown 'for improved ripple rejection'. "Xc SHOULD = R1 AT RIPPLE FREQUENCY" (That was why I asked, and I recommend using these caps to you).I am trying to use the simple circuit given by NS - a resistor and pot.
It appears to me that dick_freebird's advice to consider and eliminate wiring losses in the grounds was very well aimed.Have you created a 'star' for the grounds, keeping sense/reference grounds clear of all current-carrying grounds & the main capacitors' grounds?
Included some low-resistance High-frequency caps close to the regulator?
Complied with the manufacturer's recommendation of using low ESR input caps and even multiple output caps?
Perhaps more precise measurement data, component values and an image showing the layout would help us?Don't neglect wiring drops or ground rise. Anything outside the Kelvin return / sense points is on you, part knows nothing.
Maybe so, but we still have such PSUs on our bench quite regularly!I guess, there won't be that much people using these devices. Mainly because high current has become a domain of switching regulators since long.
Possible, but unless you have reason to suspect . . . then unlikely. One device, yes, a batch, no.It could be that I might have got my devices off a particularly bad batch.
I strongly agree with you and wish I had one in the bucket of regs to try myself to reproduce your findings. (I'd be pleased to if I had - out of sheer interest!).Linear regulators are more reliable and noise much less of a problem. So I wish to persist with this design.
I fear, no exact finding have been reported, strictly spoken. I believe, that bad regulation is seen somehow. But the repeated suggestions of placing capacitors here and there already clarify, that nobody knows, if it's an AC (stability) or a "simple" DC problem. But it can be clearly distinguished. Also the measured regulator pin-to-pin voltages under "bad regulation" conditions have never been told (as DC+AC measurements). So my initial guess about "incorrect usage of the device" hasn't been disproved yet.wish I had one in the bucket of regs to try myself to reproduce your findings
From **broken link removed** I see the text advises a cap between the 'ground' pin and circuit 0v which is illustrated with C1 = R1 at ripple frequency thus:-Not sure what is meant by putting a capacitor between device ground and 0V. Could you suggest a circuit please (DXNewcastle)?
STABILITY CONSIDERATION
Stability consideration primarily concern the phase response
of the feedback loop. In order for stable operation, the loop
must maintain negative feedback. The LM1084 requires a
certain amount series resistance with capacitive loads. This
series resistance introduces a zero within the loop to in-
crease phase margin and thus increase stability. The equiva-
lent series resistance (ESR) of solid tantalum or aluminum
electrolytic capacitors is used to provide the appropriate zero
(approximately 500 kHz).
Please refer to schematic in my post of 25th Feb.DXNewxastle: NS circuits are showing 0V as grounded, hence the capacitors are all connected with respect to 0V or ground. I have used all capacitors in the diagram. Ripple is not the problem. Your reference to Capacitor between ground pin and 0V does not make sense.
Apparently you need an 'appropriate zero' at 500KHz. Thank you very much National Semiconductor.
The problem of needing a minimum ESR along with the output capacitor can be found with nearly any linear regulator, except for a few new designs that are explicitely said to be stable with ceramic output capacitors. As the quoted datasheet snippet clarifies, regular tantal or aluminium electrolytic capacitors will provide sufficient ESR.There is no such 500KHz 'babble' about LM150/LM350 3A devices in their data sheets - obviously a completely different device design.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?