Forums

peculiar input current problem

Started by abq_guy February 3, 2009
Hello,

I am using a DC-DC converter from DATEL ( BWR-15/670-D12A). The inputs are
+15V and the outputs are +15V and -15V. The converter can give upto 670mA
of output current on both +15V and -15V individually.

I am using these output voltages to power 2 Linear LDO regulators (LT1962
and LT1964). These regulators take in the +15V and the -15V from the DC-DC
converter and convert them to +14.85V and -14.85V respectively.

I use these +14.85V and -14.85V to power 5 LTC2704 (DAC's ), 5 OP400
op-amps, and 5 LT1885 op-amps.

When I turn the power On, the DC-DC converter starts taking in about
0.375A of current, but it rises to 1.0142A, at which point the +14.85V goes
down to 1.62V and the input current drops to 0.250A.

Why is this happening ? Any explanations.

Thanks,

abq_guy


"abq_guy" <babel@bira.com> wrote in message 
news:f4KdnfWbT8x7pBXUnZ2dnUVZ_hadnZ2d@giganews.com...
> Hello, > > I am using a DC-DC converter from DATEL ( BWR-15/670-D12A). The inputs are > +15V and the outputs are +15V and -15V. The converter can give upto 670mA > of output current on both +15V and -15V individually. > > I am using these output voltages to power 2 Linear LDO regulators (LT1962 > and LT1964). These regulators take in the +15V and the -15V from the DC-DC > converter and convert them to +14.85V and -14.85V respectively. > > I use these +14.85V and -14.85V to power 5 LTC2704 (DAC's ), 5 OP400 > op-amps, and 5 LT1885 op-amps. > > When I turn the power On, the DC-DC converter starts taking in about > 0.375A of current, but it rises to 1.0142A, at which point the +14.85V > goes > down to 1.62V and the input current drops to 0.250A. > > Why is this happening ? Any explanations.
One possibility is that one rail is trying to pull the other across the 0V line. Dual supplies are happiest returning current to/from the 0V line. If the majority of the current is actually returned to another rail, then any difference in turn-on time - due to perhaps some 0V-related load on one rail and not the other - can result in one rail being established before the other, and a tug-of-war ensues... There are various workarounds, but the easiest is to introduce some additional 0V-related load on one or both of the rails to help them get established. Or, it could be something completely different ;). Steve -- http://www.fivetrees.com
On Tue, 03 Feb 2009 06:34:46 -0600, "abq_guy" <babel@bira.com> wrote:

>Hello, > >I am using a DC-DC converter from DATEL ( BWR-15/670-D12A). The inputs are >+15V and the outputs are +15V and -15V. The converter can give upto 670mA >of output current on both +15V and -15V individually. > >I am using these output voltages to power 2 Linear LDO regulators (LT1962 >and LT1964). These regulators take in the +15V and the -15V from the DC-DC >converter and convert them to +14.85V and -14.85V respectively. > >I use these +14.85V and -14.85V to power 5 LTC2704 (DAC's ), 5 OP400 >op-amps, and 5 LT1885 op-amps. > >When I turn the power On, the DC-DC converter starts taking in about >0.375A of current, but it rises to 1.0142A, at which point the +14.85V goes >down to 1.62V and the input current drops to 0.250A. > >Why is this happening ? Any explanations. >
How old is this converter ? We had a bad batch from DATEL about 3 years ago. They had manufacturing problems where their converters derated extremely quickly even at fairly moderate temperatures. They replaced the batch, but by that time we had switched to converters from Traco. See what happens if you cool the converter down a bit. Leave it in the fridge for half an hour. Regards Anton Erasmus
Anton Erasmus wrote:
> On Tue, 03 Feb 2009 06:34:46 -0600, "abq_guy" <babel@bira.com> wrote: > >> Hello, >> >> I am using a DC-DC converter from DATEL ( BWR-15/670-D12A). The inputs are >> +15V and the outputs are +15V and -15V. The converter can give upto 670mA >> of output current on both +15V and -15V individually. >> >> I am using these output voltages to power 2 Linear LDO regulators (LT1962 >> and LT1964). These regulators take in the +15V and the -15V from the DC-DC >> converter and convert them to +14.85V and -14.85V respectively. >> >> I use these +14.85V and -14.85V to power 5 LTC2704 (DAC's ), 5 OP400 >> op-amps, and 5 LT1885 op-amps. >> >> When I turn the power On, the DC-DC converter starts taking in about >> 0.375A of current, but it rises to 1.0142A, at which point the +14.85V goes >> down to 1.62V and the input current drops to 0.250A. >> >> Why is this happening ? Any explanations. >> > > How old is this converter ? We had a bad batch from DATEL about 3 > years ago. They had manufacturing problems where their converters > derated extremely quickly even at fairly moderate temperatures. > They replaced the batch, but by that time we had switched to > converters from Traco. > See what happens if you cool the converter down a bit. Leave it in the > fridge for half an hour.
Sometimes DC/DC converters can be twitchy about big capacitors on their outputs. Read the data sheet carefully to make sure you haven't broken any rules.