What is the principle of the pull-up resistor in the electric welding machine? Qingdao Aitel welding machine is the most reliable welding machine in the domestic IGBT welding machine. Let's talk about the principle of the pull-up resistance in the welding machine.
1. When the TTL circuit drives the CMOS circuit, if the high level output by the TTL circuit is lower than the highest level of the CMOS circuit (usually 3.5V), then it is necessary to connect a pull-up resistor to the output terminal of the TTL to Increase the value of the output high level.
2, OC gate circuit must add pull-up resistor before it can be used.
3. In order to increase the drive capability of output pins, pull-up resistors are often used on some single-chip microcomputer pins.
4. On the CMOS chip, in order to prevent damage caused by static electricity, the unused pins cannot be left floating. Generally, a pull-up resistor is connected to reduce the input impedance and provide a leakage path.
5. Add pull-up resistors to the pins of the chip to increase the output level, thereby improving the noise tolerance of the chip's input signal and enhancing the anti-interference ability.
6. Improve the anti-electromagnetic interference ability of the bus. If the pin is left floating, it is easier to accept external electromagnetic interference.
7. In the long-line transmission, the resistance mismatch can easily cause the reflected wave interference, and the pull-down resistance is the resistance matching, which effectively suppresses the reflected wave interference.
Pull-up resistor selection principles include:
1. It should be large enough to save power consumption and the current sink capability of the chip; the resistance is large and the current is small.
2, it should be small enough to ensure enough drive current; the resistance is small, the current is large.
3. For high-speed circuits, excessive pull-up resistors may have smooth edges. Considering
The above three points are usually selected between 1k and 10k.
