I'm looking for a way to switch an USB device's power (a mini waterpump) digitally. I've found some solutions, however I'm not sure what are the advantages/disadvantages of the different approaches, so I'd like to ask your opinions and which is the best to use.

Solution 1: Using transistors similarly to this enter image description here

Solution 2: Using a 5V LDO with shutdown pin

Solution 3: Using a dedicated USB power switch (e.g. TPS203x)


Looks like the device has the USB plug just for power input.

The circuit in option-1 looks okay. I don't know if the schematic generator automatically puts a name of "AOP605" on MOSFETs but make sure you select an N-Ch MOSFET for M1 and a P-Channel MOSFET for M2. Ones having a Vbrdss of 10V (min) and an Rds of 100-150mOhm (max) would do the job.

Using an LDO /w EN pin may simplify the circuit but the output voltage is the thing to consider. A USB port's voltage can be as low as 4.75VDC or can be as high as 5.25VDC. So the output of the LDO should be around 4.5VDC (The label on the product says that the input voltage can be as low as 3.5VDC so 4.5VDC won't harm it) which means you should use an adjustable type LDO.

Most of the load switch ICs have a current limiter mechanism inside. Some of them also have FAULT output (thermal or overcurrent). The ones with 1A current limit would do the job. They also simplify the circuit.

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  • \$\begingroup\$ Thanks! And is there any meaningful difference in terms of power dissipation/consumption? \$\endgroup\$ – Razero May 12 at 15:40
  • \$\begingroup\$ @Razero sorry, I was on mobile and I mistyped. And I revised my comment: For Option-1 and and -3 the consumption depends on the MOSFETs Rds and load current (from I²R). For Option-2, it depends on the USB port's output voltage as the dissipation is proportional to the difference (i.e. I × (VUSB - 4.5V)). Option-2 is the worst of course, especially when the port voltage is 5.25V, but the levels are not that high to worry about. Personally, I'd go for Option-2 or -3. Especially the TPS203x has a MOSFET with a very low Rds. \$\endgroup\$ – Rohat Kılıç May 13 at 4:17

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