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Why doesn't my computer USB port break when I plug in a 2A device?
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For typical AC to DC power adapters, I understand that the device draws the current it needs from the adapter. If it pulls more than the adapter can supply, this can cause overheating and lead to breaking the adapter.
Following this... I am always charging my phone or tablet on 1A USB chargers or in normal PC USB ports, yet I have never experienced a broken USB port resulting from this.
My question is:
Do USB ports or devices typically have a mechanism to regulate current to avoid overloading ports?
I'm mostly thinking in the context of devices which charge via USB.
power-supply usb charger charging
edited 57 mins ago
Michel Keijzers
4,75062149
asked 2 hours ago
RTbecard
1205
add a comment |Â
up vote
1
down vote
favorite
For typical AC to DC power adapters, I understand that the device draws the current it needs from the adapter. If it pulls more than the adapter can supply, this can cause overheating and lead to breaking the adapter.
Following this... I am always charging my phone or tablet on 1A USB chargers or in normal PC USB ports, yet I have never experienced a broken USB port resulting from this.
My question is:
Do USB ports or devices typically have a mechanism to regulate current to avoid overloading ports?
I'm mostly thinking in the context of devices which charge via USB.
power-supply usb charger charging
edited 57 mins ago
Michel Keijzers
4,75062149
asked 2 hours ago
RTbecard
1205
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
For typical AC to DC power adapters, I understand that the device draws the current it needs from the adapter. If it pulls more than the adapter can supply, this can cause overheating and lead to breaking the adapter.
Following this... I am always charging my phone or tablet on 1A USB chargers or in normal PC USB ports, yet I have never experienced a broken USB port resulting from this.
My question is:
Do USB ports or devices typically have a mechanism to regulate current to avoid overloading ports?
I'm mostly thinking in the context of devices which charge via USB.
power-supply usb charger charging
edited 57 mins ago
Michel Keijzers
4,75062149
asked 2 hours ago
RTbecard
1205
For typical AC to DC power adapters, I understand that the device draws the current it needs from the adapter. If it pulls more than the adapter can supply, this can cause overheating and lead to breaking the adapter.
Following this... I am always charging my phone or tablet on 1A USB chargers or in normal PC USB ports, yet I have never experienced a broken USB port resulting from this.
My question is:
Do USB ports or devices typically have a mechanism to regulate current to avoid overloading ports?
I'm mostly thinking in the context of devices which charge via USB.
power-supply usb charger charging
power-supply usb charger charging
edited 57 mins ago
Michel Keijzers
4,75062149
asked 2 hours ago
RTbecard
1205
edited 57 mins ago
Michel Keijzers
4,75062149
asked 2 hours ago
RTbecard
1205
edited 57 mins ago
Michel Keijzers
4,75062149
edited 57 mins ago
Michel Keijzers
4,75062149
edited 57 mins ago
Michel Keijzers
4,75062149
4,75062149
asked 2 hours ago
RTbecard
1205
asked 2 hours ago
RTbecard
1205
asked 2 hours ago
RTbecard
1205
1205
add a comment |Â
add a comment |Â
3 Answers
3
active
oldest
votes
up vote
4
down vote
accepted
To be compatible with the original standard, USB devices should not draw more than 100mA, until they have negotiated with the host, to find out what it can supply. After that, they can draw up to 500mA.
Later revisions allow power supplies to hold their data lines in particular states, to signal to the device being charged that they are a power supply, with a certain capability.
Not all USB devices are compliant to the standard, but just draw full current anyway, USB toys commonly do this.
answered 2 hours ago
Neil_UK
69.7k272153
add a comment |Â
up vote
2
down vote
The answer is yes, they do.
USB includes a fairly elaborate protocol that allows devices and hosts to negotiate the amount of power that the device can use.
answered 2 hours ago
Dave Tweed♦
108k9130233
add a comment |Â
up vote
1
down vote
Historically:
- really old mainboards connect USB power pins to the 5V power rail, with no protection
- power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards.
- USB port power control was added to root hubs, allowing the host to turn off power to ports programmatically (with the hub controller switching an external "power" FET). These supply a lot of power to the ports, and have no meaningful protection besides using the FET as a current limiter, which is generally a bad idea for prolonged time as these are not usually cooled.
- the control FET was later integrated into the root hub as manufacturing processes improved to a point where you could run a few hundred mA through what is otherwise a logic IC. This setup has lower current carrying capability, and shorting USB ports will usually destroy the southbridge IC and/or cause a reboot.
- current monitoring and emergency shutdown were added to the controllers as well as processes permitted.
There are also some older mainboards that implement current monitoring as discrete components (increasing board cost, but giving robustness), but on consumer boards, expect the cheapest possible approach.
Some modern boards also use the same kind of integrated voltage/current controller that usually provides CPU and chipset power to control other circuits, as these ICs are sufficiently cheap that duplicating the logic around them saves enough engineering effort to make them a good contender to "dumb" FETs. On such boards you'd probably be able to draw exactly 2.000A, but current monitoring and reporting may be limited as communication between the USB root hub and the power controller is just "enable" and "error" signals.
answered 48 mins ago
Simon Richter
5,99811025
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
To be compatible with the original standard, USB devices should not draw more than 100mA, until they have negotiated with the host, to find out what it can supply. After that, they can draw up to 500mA.
Later revisions allow power supplies to hold their data lines in particular states, to signal to the device being charged that they are a power supply, with a certain capability.
Not all USB devices are compliant to the standard, but just draw full current anyway, USB toys commonly do this.
answered 2 hours ago
Neil_UK
69.7k272153
add a comment |Â
up vote
4
down vote
accepted
To be compatible with the original standard, USB devices should not draw more than 100mA, until they have negotiated with the host, to find out what it can supply. After that, they can draw up to 500mA.
Later revisions allow power supplies to hold their data lines in particular states, to signal to the device being charged that they are a power supply, with a certain capability.
Not all USB devices are compliant to the standard, but just draw full current anyway, USB toys commonly do this.
answered 2 hours ago
Neil_UK
69.7k272153
add a comment |Â
up vote
4
down vote
accepted
up vote
4
down vote
accepted
To be compatible with the original standard, USB devices should not draw more than 100mA, until they have negotiated with the host, to find out what it can supply. After that, they can draw up to 500mA.
Later revisions allow power supplies to hold their data lines in particular states, to signal to the device being charged that they are a power supply, with a certain capability.
Not all USB devices are compliant to the standard, but just draw full current anyway, USB toys commonly do this.
answered 2 hours ago
Neil_UK
69.7k272153
To be compatible with the original standard, USB devices should not draw more than 100mA, until they have negotiated with the host, to find out what it can supply. After that, they can draw up to 500mA.
Later revisions allow power supplies to hold their data lines in particular states, to signal to the device being charged that they are a power supply, with a certain capability.
Not all USB devices are compliant to the standard, but just draw full current anyway, USB toys commonly do this.
answered 2 hours ago
Neil_UK
69.7k272153
answered 2 hours ago
Neil_UK
69.7k272153
answered 2 hours ago
Neil_UK
69.7k272153
answered 2 hours ago
Neil_UK
69.7k272153
69.7k272153
add a comment |Â
add a comment |Â
up vote
2
down vote
The answer is yes, they do.
USB includes a fairly elaborate protocol that allows devices and hosts to negotiate the amount of power that the device can use.
answered 2 hours ago
Dave Tweed♦
108k9130233
add a comment |Â
up vote
2
down vote
The answer is yes, they do.
USB includes a fairly elaborate protocol that allows devices and hosts to negotiate the amount of power that the device can use.
answered 2 hours ago
Dave Tweed♦
108k9130233
add a comment |Â
up vote
2
down vote
up vote
2
down vote
The answer is yes, they do.
USB includes a fairly elaborate protocol that allows devices and hosts to negotiate the amount of power that the device can use.
answered 2 hours ago
Dave Tweed♦
108k9130233
The answer is yes, they do.
USB includes a fairly elaborate protocol that allows devices and hosts to negotiate the amount of power that the device can use.
answered 2 hours ago
Dave Tweed♦
108k9130233
answered 2 hours ago
Dave Tweed♦
108k9130233
answered 2 hours ago
Dave Tweed♦
108k9130233
answered 2 hours ago
Dave Tweed♦
108k9130233
108k9130233
add a comment |Â
add a comment |Â
up vote
1
down vote
Historically:
- really old mainboards connect USB power pins to the 5V power rail, with no protection
- power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards.
- USB port power control was added to root hubs, allowing the host to turn off power to ports programmatically (with the hub controller switching an external "power" FET). These supply a lot of power to the ports, and have no meaningful protection besides using the FET as a current limiter, which is generally a bad idea for prolonged time as these are not usually cooled.
- the control FET was later integrated into the root hub as manufacturing processes improved to a point where you could run a few hundred mA through what is otherwise a logic IC. This setup has lower current carrying capability, and shorting USB ports will usually destroy the southbridge IC and/or cause a reboot.
- current monitoring and emergency shutdown were added to the controllers as well as processes permitted.
There are also some older mainboards that implement current monitoring as discrete components (increasing board cost, but giving robustness), but on consumer boards, expect the cheapest possible approach.
Some modern boards also use the same kind of integrated voltage/current controller that usually provides CPU and chipset power to control other circuits, as these ICs are sufficiently cheap that duplicating the logic around them saves enough engineering effort to make them a good contender to "dumb" FETs. On such boards you'd probably be able to draw exactly 2.000A, but current monitoring and reporting may be limited as communication between the USB root hub and the power controller is just "enable" and "error" signals.
answered 48 mins ago
Simon Richter
5,99811025
add a comment |Â
up vote
1
down vote
Historically:
- really old mainboards connect USB power pins to the 5V power rail, with no protection
- power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards.
- USB port power control was added to root hubs, allowing the host to turn off power to ports programmatically (with the hub controller switching an external "power" FET). These supply a lot of power to the ports, and have no meaningful protection besides using the FET as a current limiter, which is generally a bad idea for prolonged time as these are not usually cooled.
- the control FET was later integrated into the root hub as manufacturing processes improved to a point where you could run a few hundred mA through what is otherwise a logic IC. This setup has lower current carrying capability, and shorting USB ports will usually destroy the southbridge IC and/or cause a reboot.
- current monitoring and emergency shutdown were added to the controllers as well as processes permitted.
There are also some older mainboards that implement current monitoring as discrete components (increasing board cost, but giving robustness), but on consumer boards, expect the cheapest possible approach.
Some modern boards also use the same kind of integrated voltage/current controller that usually provides CPU and chipset power to control other circuits, as these ICs are sufficiently cheap that duplicating the logic around them saves enough engineering effort to make them a good contender to "dumb" FETs. On such boards you'd probably be able to draw exactly 2.000A, but current monitoring and reporting may be limited as communication between the USB root hub and the power controller is just "enable" and "error" signals.
answered 48 mins ago
Simon Richter
5,99811025
add a comment |Â
up vote
1
down vote
up vote
1
down vote
Historically:
- really old mainboards connect USB power pins to the 5V power rail, with no protection
- power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards.
- USB port power control was added to root hubs, allowing the host to turn off power to ports programmatically (with the hub controller switching an external "power" FET). These supply a lot of power to the ports, and have no meaningful protection besides using the FET as a current limiter, which is generally a bad idea for prolonged time as these are not usually cooled.
- the control FET was later integrated into the root hub as manufacturing processes improved to a point where you could run a few hundred mA through what is otherwise a logic IC. This setup has lower current carrying capability, and shorting USB ports will usually destroy the southbridge IC and/or cause a reboot.
- current monitoring and emergency shutdown were added to the controllers as well as processes permitted.
There are also some older mainboards that implement current monitoring as discrete components (increasing board cost, but giving robustness), but on consumer boards, expect the cheapest possible approach.
Some modern boards also use the same kind of integrated voltage/current controller that usually provides CPU and chipset power to control other circuits, as these ICs are sufficiently cheap that duplicating the logic around them saves enough engineering effort to make them a good contender to "dumb" FETs. On such boards you'd probably be able to draw exactly 2.000A, but current monitoring and reporting may be limited as communication between the USB root hub and the power controller is just "enable" and "error" signals.
answered 48 mins ago
Simon Richter
5,99811025
Historically:
- really old mainboards connect USB power pins to the 5V power rail, with no protection
- power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards.
- USB port power control was added to root hubs, allowing the host to turn off power to ports programmatically (with the hub controller switching an external "power" FET). These supply a lot of power to the ports, and have no meaningful protection besides using the FET as a current limiter, which is generally a bad idea for prolonged time as these are not usually cooled.
- the control FET was later integrated into the root hub as manufacturing processes improved to a point where you could run a few hundred mA through what is otherwise a logic IC. This setup has lower current carrying capability, and shorting USB ports will usually destroy the southbridge IC and/or cause a reboot.
- current monitoring and emergency shutdown were added to the controllers as well as processes permitted.
There are also some older mainboards that implement current monitoring as discrete components (increasing board cost, but giving robustness), but on consumer boards, expect the cheapest possible approach.
Some modern boards also use the same kind of integrated voltage/current controller that usually provides CPU and chipset power to control other circuits, as these ICs are sufficiently cheap that duplicating the logic around them saves enough engineering effort to make them a good contender to "dumb" FETs. On such boards you'd probably be able to draw exactly 2.000A, but current monitoring and reporting may be limited as communication between the USB root hub and the power controller is just "enable" and "error" signals.
answered 48 mins ago
Simon Richter
5,99811025
edited 36 mins ago
answered 48 mins ago
Simon Richter
5,99811025
answered 48 mins ago
Simon Richter
5,99811025
answered 48 mins ago
Simon Richter
5,99811025
5,99811025
add a comment |Â
add a comment |Â
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