About WallWarts and Bricks...
Posted: Sat Dec 29, 2018 12:29 am
INTRO
There was a recent post about problems with a 9V adapter ("Let the smoke out", Dec24/18) for the DSO Shell. I was going to reply there but thought this might serve better as a generalized post about using plug-in power supplies (as opposed to batteries).
TEST
First: *always* measure the output voltage of a new/unknown power supply before you connect it to the DSO Shell. As noted below, some actual supply voltages are not what they're rated to be.
DEFINITIONS
I'm in Canada, so am speaking from North American experience. For other countries, there may be differences.
a. WallWart
Think of a wallwart like a wart on the hand -- the wart is a "bump" that sticks out above the skin's surface. The wallwart is a bump that sticks out from the wall's surface. The shape may be close to a cube, or somewhat oblong. It plugs directly into the wall and has a low-voltage DC lead coming out of it, usually terminating in a plug of some kind.
b. Brick
Named for it's shape -- an oblong flat rectangle, like a building brick. A brick has 2 power cords -- one for AC-in, the other for DC-out, each ending in a plug of some kind.
DETAILS
a. WallWarts...
a.1 Unregulated
The original wallwart (it's been around for many years) has a transformer, along with rectifier and filter capacitor built in. It's generally cube-shaped and, because of the transformer, feels heavy for its size.
The rectifier is a single diode, and there is no regulator. So, the output is half-wave, with lots of ripple. The actual output voltage will be considerably higher than the nominal rating. Some examples (based on 120VAC source, and no load on the output)...
- 9V measures 15.9V actual
- 12V measures 19.3 actual
- 15V measures 21.6 actual
Google will find you websites that explain half-wave and full-wave rectification, and the math behind the actual output values.
This is an unregulated unit: a.2 Regulated
This is a "newer" variety. It may be somewhat oblong in shape, and will be relatively light-weight. These have a switching supply built in (no transformer, thus the light weight), so put out a full-wave, regulated voltage. Because the output is regulated, what you see is what you get, ie: A nominal 9V rated wallwart will actually measure 9V out.
This is a regulated unit:
b. Bricks...
I haven't opened any of these, but I have seen "heavy" and "light" units, which leads me to think the heavier ones have a transformer (not sure what else), and the lighter ones use a switching supply. The few brick outputs I've measured have been 12V units, and they've all measured just over 12V (12.3 - 12.6) out. This suggests they're all regulated.
This is a Brick:
WRAPPING UP
Be aware that some power supplies can have an output voltage that's different from the rated/nominal value. If in doubt about a power supply, *test* the unit before using.
Hopefully this info will help save someone grief from unnecessary burnout.
.
.
There was a recent post about problems with a 9V adapter ("Let the smoke out", Dec24/18) for the DSO Shell. I was going to reply there but thought this might serve better as a generalized post about using plug-in power supplies (as opposed to batteries).
TEST
First: *always* measure the output voltage of a new/unknown power supply before you connect it to the DSO Shell. As noted below, some actual supply voltages are not what they're rated to be.
DEFINITIONS
I'm in Canada, so am speaking from North American experience. For other countries, there may be differences.
a. WallWart
Think of a wallwart like a wart on the hand -- the wart is a "bump" that sticks out above the skin's surface. The wallwart is a bump that sticks out from the wall's surface. The shape may be close to a cube, or somewhat oblong. It plugs directly into the wall and has a low-voltage DC lead coming out of it, usually terminating in a plug of some kind.
b. Brick
Named for it's shape -- an oblong flat rectangle, like a building brick. A brick has 2 power cords -- one for AC-in, the other for DC-out, each ending in a plug of some kind.
DETAILS
a. WallWarts...
a.1 Unregulated
The original wallwart (it's been around for many years) has a transformer, along with rectifier and filter capacitor built in. It's generally cube-shaped and, because of the transformer, feels heavy for its size.
The rectifier is a single diode, and there is no regulator. So, the output is half-wave, with lots of ripple. The actual output voltage will be considerably higher than the nominal rating. Some examples (based on 120VAC source, and no load on the output)...
- 9V measures 15.9V actual
- 12V measures 19.3 actual
- 15V measures 21.6 actual
Google will find you websites that explain half-wave and full-wave rectification, and the math behind the actual output values.
This is an unregulated unit: a.2 Regulated
This is a "newer" variety. It may be somewhat oblong in shape, and will be relatively light-weight. These have a switching supply built in (no transformer, thus the light weight), so put out a full-wave, regulated voltage. Because the output is regulated, what you see is what you get, ie: A nominal 9V rated wallwart will actually measure 9V out.
This is a regulated unit:
b. Bricks...
I haven't opened any of these, but I have seen "heavy" and "light" units, which leads me to think the heavier ones have a transformer (not sure what else), and the lighter ones use a switching supply. The few brick outputs I've measured have been 12V units, and they've all measured just over 12V (12.3 - 12.6) out. This suggests they're all regulated.
This is a Brick:
WRAPPING UP
Be aware that some power supplies can have an output voltage that's different from the rated/nominal value. If in doubt about a power supply, *test* the unit before using.
Hopefully this info will help save someone grief from unnecessary burnout.
.
.