"강한"풀 (위 / 아래) 저항은 비교적 낮은 값 중 하나이고 "약한"저항은 상대적으로 높은 값입니다.
예를 들어, 풀다운 저항은 I / O 핀을 낮게 유지하는 데 사용되지만, 해당 핀에서 V CC로 연결된 버튼 은 눌렀을 때 높은 전류를 가져옵니다. V CC 에서 핀으로보다 많은 전류가 흐르기 때문입니다 GND에 핀.
이러한 상황에서는 저항 값을 사용하여 핀을 낮게 유지할 수 있으며 버튼을 누르면 항상 "재정의"할 수 있습니다. 그러면 풀다운 저항이 강하거나 약한 지 어떻게 알 수 있습니까?
"강한"대 "약한"은 내부 풀다운 저항과 같이 이러한 저항 중 하나를 회로의 다른 저항과 비교할 때만 적용됩니까?
답변:
강함 은 낮은 저항을 의미 합니다. 약함 은 높은 저항을 의미 합니다. 코스 중 낮은 및 높은 상대 용어는 등이다 강력한 및weak. The reference for this relationship must be inferred from context.
강력한 또는 낮은 저항 부하 용량 (종종 입력 게이트 용량, 및 PCB 트레이스 커패시턴스)을 형성 시상수가 작으므로 풀업 / 저항 다운이 양호하므로 시간이 짧은 것 하강 / 상승.
강력한 의도 결합 및 EMI 노이즈 전류가 작은 잡음 전압을 발생하기 때문에 풀 - 업 / 다운 저항 좋다. (옴의 법칙에 대해 생각하십시오)
약한 또는 고 저항 은 저항에 대한 작업에 구동 회로에서 많은 전류를 필요로하지 않기 때문에 풀업은 / 저항 아래로 좋다. 따라서 배터리 수명이 길어지고 부품이 작아지고 뜨거워지지 않습니다.
Of course, you usually want all of these things, but a resistor can't be both. A discussion about strong vs. weak is usually clarifying which of these concerns (or perhaps others) are more important for a particular application.
A "weak" pull resistor is usually a high value resistor that only allows a small amount of current through, and can quickly be overwritten, but takes longer to reassert itself.
A "strong" pull resistor is usually a low value resistor, allows more current through, takes longer to be overwritten, but can quickly reassert a line.
They are completely relative to your needs, not just other pull resistors like internal ones.
In your button scenario, the time it takes to switch from one state to the other isn't important, so weak vs strong doesn't apply there. But weak vs strong does apply in the practical matter of Current Consumption. A strong pull resistor would, when the button is pressed, cause a large drain of current from vcc through the resistor to ground. A weak pull resistor would cause a small drain of current. Theoretically any resistor would work, but for practical purposes, a weak resistor is used because unnecessary high current drains can cause issues and can easily be avoided by sizing the resistor correctly.
Does "strong" vs "weak" only apply when one such resistor is being compared to other resistances in the circuit, such as an internal pull-down resistor?
Yes, this is exactly it. Strong and weak simply refer to the relative drive strength of the component. A pull up/down resistor's value has no association to whether it is strong or weak. Only in knowing the context of the other connections to the net can you determine if a pull-up is strong or weak.
There are other things to consider when selecting the value of a pull-up or pull-down. For example, depending on the capacitance of the circuit, too week of a pull-up/down will limit how quickly the voltage change occurs. On the other hand, too strong of a pull-up/down will draw excessive current through whatever is trying to pull the other way. These are often considerations in selecting the pull-ups for an I2C (open drain) bus, for example.
However, the place I see "weak pull-ups" typically used is inside microcontroller chips, typically on I/O pins. These are mainly used to guarantee that an input won't float if not connected. The pull-ups are weak both to limit their effect on the external circuitry and to limit the power dissipated inside the chip.
When you put a large resistance for ground coupling, the voltage developed across it would prevent the node from getting to ground potential. On the other hand, if you put small resistance to the ground, the node potential would be more close to V(gnd). If R(gnd) is high, it would not be able to pull down your node to zero potential. So, you can consider this as "weak" pull down, and vice-versa. Of course, this is just for comparison purpose only (with other components in your circuit)