wall warts: constant specified current though universal input voltage?

How come the input drawing current be constant (1.5A) even though it shows that the adapter is universal input (100-240V)? I mean that the power supply voltage varies in different locations still how come the current be same.

• The input current will vary with the input voltage and with the load current. The rating printed on the supply is a maximum. – The Photon Jul 15 '18 at 4:37
• And probably a fairly conservative one. Even at maximum load and minimum input voltage, if it draws 1.5 A it's only about 66% efficient. (Maybe 1.5 A is the limit for some fuse inside the device). – The Photon Jul 15 '18 at 4:39
• @SolarMike Err, I would say the tilde is after the voltage rating to indicate AC. – winny Jul 15 '18 at 8:17
• @winny the statement of frequency also does that, but given no spacing or punctuation then you could be right. – Solar Mike Jul 15 '18 at 8:25
• @SolarMike It’s strange. – winny Jul 15 '18 at 9:19

The input current is not constant. The 1.5 A figure refers to the worst case, meaning the value that is guaranteed not to be exceeded under all combinations of valid conditions.

In this case, the combination of conditions is probably with 100 V in and 4.62 A out, although that is not explicitly stated, so you shouldn't rely on that.

• Could you please elucidate the conditions of minimum input voltage and maximum output current for drawing input current. – aditya Jul 15 '18 at 13:45
• @adi: For switching power supplies, which this clearly is, the input power is the output power, plus a little extra to make up for losses. The maximum output power is 19.5 V at 4.62 A, which is 90 W. The input power is the input voltage times the input current. With the power fixed, the current goes up as the voltage goes down. – Olin Lathrop Jul 15 '18 at 21:41

The marking gives you the maximum current, not the typical current. As others have said that will generally occur at minimum input voltage and maximum output current (and maximum ambient temperature, where losses are greatest). Typically input current will be minimum under the opposite conditions, and some adapters may have an extra-low-power mode for when the load side is unplugged.

If you are interested in the power consumed rather than current (the input will likely not have power factor correction (PFC)) then refer to the efficiency rating V which indicates a minimum efficiency of 87%, so at full output current it should draw less than 103W.

• could you please elucidate the math you have done. – aditya Jul 15 '18 at 14:35
• 90W/0.87 =103W. – Spehro Pefhany Jul 15 '18 at 14:57
• from where did you get 87% efficiency?also explain briefly that PFC – aditya Jul 15 '18 at 15:02
• From the specifications for "V" efficiency, as stated in my answer. Power factor correction uses active circuitry to attempt to make V*A approach Watts (rather than being much higher), too much to explain in one comment here. – Spehro Pefhany Jul 15 '18 at 15:25