Large AC voltage between switching power supply output ground and AC ground

[Steve]

I have noticed a large voltage difference between the low (ground)
side output of wall-wart style switching power supplies and the AC
power ground. It is enough to provide a slight tngle shock when
touching the DC ground and something connected to AC power ground. Is
this a characteristic of switching supplies ? The one linear supply I
check did not have this issue. Having a 3-prong ground AC input does
not avoid this as some supplies apparently have no connection between
their AC input ground and their output ground.

I sometimes use two supplies to generate a +/- supply by connecting
the output of one to ground of the other theerby having the second
supply's ground be the negative supply. This requires the DC output
ground be isolated from AC input ground. Are there any such isolated
supplies that are switching style but do not have such large AC
voltages between their output and AC ground ?

CUI model EPS050100 5 Volt 1 Amp switching 2-prong AC input has 50 V

CUI DPR050030-P6 5 Volt 300 mA linear style 2-prong AC input has 5 V

CINCON TR36A-05 5 Volt 4 Amp switching style 2-prong AC input has 50 V

CUI EPA-301DN-24 24 Volt 1.25 Amp switching style 3-prong grounded AC
input has 60 V. There is not ohmic continuity between its AC input
ground and output DC ground.

CUI 3A-621DN24 24 Volt 2.5 Amp switching style 3-prong grounded AC
input has 0 V. There is ohmic continuity between its AC input ground
and output DC ground.

ITE PW149RA4803F01 48 Volt 0.4 Amp switching style 3-prong grounded AC
input has 23 V. There is not ohmic continuity between its AC input
ground and output DC ground.

 

[Eeyore]

I have noticed a large voltage difference between the low (ground)
side output of wall-wart style switching power supplies and the AC
power ground. It is enough to provide a slight tngle shock when
touching the DC ground and something connected to AC power ground. Is
this a characteristic of switching supplies ?

In a word. YES.

Graham

 

[Nobody]

I have noticed a large voltage difference between the low (ground)
side output of wall-wart style switching power supplies and the AC
power ground. It is enough to provide a slight tngle shock when
touching the DC ground and something connected to AC power ground. Is
this a characteristic of switching supplies ?

Yes. They normally connect the DC ground to both live and neutral via
small (1nF-10nF) class Y capacitors.

The one linear supply I
check did not have this issue. Having a 3-prong ground AC input does
not avoid this as some supplies apparently have no connection between
their AC input ground and their output ground.

I sometimes use two supplies to generate a +/- supply by connecting
the output of one to ground of the other theerby having the second
supply's ground be the negative supply. This requires the DC output
ground be isolated from AC input ground.

You can still do this. The connection between the two grounds is
via capacitors, so it won't pass DC.

Are there any such isolated
supplies that are switching style but do not have such large AC
voltages between their output and AC ground ?

"Wall-wart" style switching PSUs invariably have these capacitors to
filter out EMI. There are problably some without them (medical?), but
expect them to be significantly more expensive.