In the picture, 1 input PWM signal (10hz), 2 input constant current source or constant voltage source, 3 output connected to LED. The problem is as follows:
(1) When two constant voltage sources are connected, the LED on the output end can flash according to the frequency of pwm;
(2) When two constant current sources are connected, the LED on the output end is always on.
Do not understand the second case, and how to solve it? Please guide, thank you!
Benjamin 發表於 August 7, 2020
This kind of analog switch is generally integrated with a MOS tube. According to your logic level and datasheet, it should be PMOS type, that is, VGS is turned on with a negative value. When you add a current source, your PMOS has a large input impedance. , Resulting in a very high voltage at the VS terminal, then no matter if your PWM is high or low, you can see that VGS always meets the threshold conduction condition and it will always be turned on. Adding a resistance to ground should be fine. .
Hannah 發表於 August 7, 2020
Oh, the single SPST specification of TS523166 I read before, there is an inverter, this is different, but the principle of NMOS is still similar, because the input impedance of the current source is very high, no matter what the state of NO1 is, All satisfy the condition of VGS>Vth.
