t_maggot
Member level 3
ne555 monostable circuit
I have a strange problem with the (classic and very simple) design of a timer with ne555.
The circuit is the standard monostable configuration, with DISCHARGE(7) and THRESHOLD(6) connected, RESET(4) tied to V+(12V), TRIGGER(2) connected to V+ through 10k resistor, 22uF capacitor between DISCHARGE and ground, 100n on CONTROL VOLTAGE(5) and ground, and 0->4M7 variable resistor between DISCHARGE(6-7) and V+.
The behavior is: as the trigger pulse applied,the output goes high and the Voltage on 6-7pins goes to 0 and then begins to rise because the capacitor charge through the var. resistor (ok so far). According to theory as the voltage reaches a threshold level (about 2/3 V+) the output must goes off, and the capacitors will discharge trough an internal transistor over the DISCHARGE pin. But no! In my circuit the voltage of the 6-7pin remains just below the threshold level (~8V) and stuck in this whit output high! (That it is true for var.resistor values>0M5). IF in this situation i give a trigger pulse, with the release of trigger from ground the output goes low! Again IF in this situation i touch the CONTROL VOLTAGE pin again the output comes back low!
It seems that there is the currents: [capacitor---->DISCHARGE(6-7)] == [V+ ---->var.resistor---->capacitor]. While the V on 6-7pins stays just below the threshold level. BUT WHY ? Any help appreciated.
I have a strange problem with the (classic and very simple) design of a timer with ne555.
The circuit is the standard monostable configuration, with DISCHARGE(7) and THRESHOLD(6) connected, RESET(4) tied to V+(12V), TRIGGER(2) connected to V+ through 10k resistor, 22uF capacitor between DISCHARGE and ground, 100n on CONTROL VOLTAGE(5) and ground, and 0->4M7 variable resistor between DISCHARGE(6-7) and V+.
The behavior is: as the trigger pulse applied,the output goes high and the Voltage on 6-7pins goes to 0 and then begins to rise because the capacitor charge through the var. resistor (ok so far). According to theory as the voltage reaches a threshold level (about 2/3 V+) the output must goes off, and the capacitors will discharge trough an internal transistor over the DISCHARGE pin. But no! In my circuit the voltage of the 6-7pin remains just below the threshold level (~8V) and stuck in this whit output high! (That it is true for var.resistor values>0M5). IF in this situation i give a trigger pulse, with the release of trigger from ground the output goes low! Again IF in this situation i touch the CONTROL VOLTAGE pin again the output comes back low!
It seems that there is the currents: [capacitor---->DISCHARGE(6-7)] == [V+ ---->var.resistor---->capacitor]. While the V on 6-7pins stays just below the threshold level. BUT WHY ? Any help appreciated.