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I have a monitor that requires 19V 1.2A. Laptop charger outputs 18.5V 3.5A. The polarity is the same.
Will slightly 0.5V lower voltage damage the monitor and is there something else that needs to be taken into consideration?
ssam
Posted 2015-10-27T17:25:06.147
Reputation: 51
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Most likely this will be just fine. The supply will have no difficulty supplying the 1.2A the monitor requires and devices typically have a tolerance for variation of the input voltage of at least 5%.
The input voltage runs a DC-to-DC converter inside the monitor that regulates the output provided to the circuits inside the monitor. The converter will provide the same output voltages and thus the circuits inside the monitor will function the same and draw the same amount of current. Because the input voltage is slightly lower, the constant power output means the input current will have to be slightly higher to supply that same power. Because the converter's switching resistance is effectively constant, the converter will run slightly hotter due to the increased current. This should not be a problem as all the differences involved are small.
David Schwartz
Posted 2015-10-27T17:25:06.147
Reputation: 58 310
@LevenTech The power output will be constant because the circuits inside the monitor (the ones the DC-to-DC converter powers) see the same voltage (the regulated output of the DC-to-DC converter) and do the same work, therefore they draw the same current. Same current and same voltage means same power. The converter's efficiency may drop a bit, so it may draw a tiny bit more power. What components do you think "are not designed for anything more than 1.2A"? And where do you think more than 1.2A will flow and why? – David Schwartz – 2015-10-27T18:07:14.543
Well you're right - if there's a circuit in the monitor that regulates power, then it will be constant. In that case, the power regulation circuit would pull extra current out of a power supply with lower voltage. But really neither of us knows whether that power regulation circuit exists. If it's a cheaper monitor that doesn't have a power regulation circuit, it would act like a plain resistor. In that case, a lower voltage would generate a lower current. – LevenTech – 2015-10-27T18:19:37.960
@LevenTech I know that a power regulation circuit exists. I understand the design of monitors. The cheapest monitors in the world still require a low, regulated voltage to run their electronics. The idea of a passive monitor that acts like a resistor is comical. – David Schwartz – 2015-10-27T18:21:23.097
@DavidSchwartz You're right. It works just fine. At least for now :) I assumed it would work but had some doubts if maybe there's something that's oversensitive and might be damaged. – ssam – 2015-10-27T18:46:30.113