EMRFD Message Archive 3110
Message Date From Subject 3110 2009-05-24 08:44:15 WA0ITP Quiet Regulators
bench for powering small projects, especially receivers. I would like to use a
regulator (more than one for different voltages maybe) fed by my shack's linear
20A station power supply.
Does anyone know of comparison measurements between different regulators, or
have a favorite circuit?
Thanx for any info
-----------------------------
I love this radio stuff !
72, 73 Terry, WAØITP
www.wa0itp.com
www.4sqrp.com
www.qrpspots.com3113 2009-05-24 09:08:11 ehydra Re: Quiet Regulators
> Glad to see the discussion about noisy regulators. I'm using batteries on theA battery is low-noise but beware of small random steps at the output.
> bench for powering small projects, especially receivers. I would like to use a
> regulator (more than one for different voltages maybe) fed by my shack's linear
> 20A station power supply.
>
> Does anyone know of comparison measurements between different regulators, or
> have a favorite circuit?
>
In fact, to find noise-problems in a prototype I replace the
wall-supplied supply with a small battery and look if the noise goes
lower. Especially important if the ciruit is connected to a PC - for
example because the digital part of the circuit will be programmed
several times by a USB programming adapter.
This will also isolate the circuit to avoid a noisy ground.
-
Another very complicated device is the MAX3232 and his friends! I got
really problems making the charge-pump quiet. The pulses are very fast
and randomly depend on actual load on the RS232 transmit pin.
- Henry
--
www.ehydra.dyndns.info3125 2009-05-25 13:22:51 Glen Leinweber Re: Quiet Regulators
to clean up power supply noise from a noisy
regulator - referred to in the article:
"Helical Resonator Oscillator" by Harold Johnson W4ZCB
It is also contained in this web reference:
<http://www.wenzel.com/documents/finesse.html>
Such a circuit can help the low-frequency (+ popcorn)
noise that is very hard to expunge from noisy regulators.
Good for driving oscillator, VCO's in PLLs. Can help
reduce noise on the power supply 40dB if trimmed
carefully.
For unregulated noise suppression:
A transistor emitter follower is sometimes used as a
"capacitor multiplier", where a capacitor is tied from
base to ground, and a large value resistor is connected
from collector to base (output at emitter). This is a low-
pass filter meant to clean up noise and low-frequency
hum - not so good where DC stability is required.
These things very often oscillate at VHF or UHF at
low amplitude. A ferrite bead on the base, or a UHF
bypass at emitter can tame it.
You can get a hint that it is oscillating by probing
with a DVM - the first measurements after probing are
high, settling to a lower value after a second or two.
A non-oscillating circuit shows more stable DC voltages.
Keep in mind that many regulators start with a low-voltage
buried-zener reference (perhaps 1.2v) and scale up
to higher voltages with on-board op-amp - noise scales
up too.3126 2009-05-25 14:07:43 michael taylor Re: Quiet Regulators 3127 2009-05-25 14:38:49 WA0ITP Quiet Regulators
-----------------------------
I love this radio stuff !
72, 73 Terry, WAØITP
www.wa0itp.com
www.4sqrp.com
www.qrpspots.com