This project was started along with the HF Amplifier. The Circuit breaker is necessary to protect the HF Amplifier from overcurrent condition.
The schematic as below :
Initially, ON/OFF function is done by using LM555 IC. We use RS-Flipflop in 555 to control the High-side Switch. After power-on, the flipflop is reset. So, the switch is always in OFF condition after power-on.
To turn on the switch, trigger the 555 by grounding the TRIG input (pin 2) momentarily. A small capacitor will make sure that the trigger is just enough. The flipflop will be set.
On turning OFF, a high voltage to THRES input (pin 7) will reset the flipflop. Also momentarily. We use a PNP transistor that will conduct if the base is grounded.
LM311 is used as comparator to detect whether current has go beyond the limit set. Then output of this comparator will trigger LM555 RS-Flipflop to reset.
Using the NE555 and LM311 give several improvements :
The finished (still prototype) picture :
Front View
Rear View
The schematic as below :
Initially, ON/OFF function is done by using LM555 IC. We use RS-Flipflop in 555 to control the High-side Switch. After power-on, the flipflop is reset. So, the switch is always in OFF condition after power-on.
To turn on the switch, trigger the 555 by grounding the TRIG input (pin 2) momentarily. A small capacitor will make sure that the trigger is just enough. The flipflop will be set.
On turning OFF, a high voltage to THRES input (pin 7) will reset the flipflop. Also momentarily. We use a PNP transistor that will conduct if the base is grounded.
LM311 is used as comparator to detect whether current has go beyond the limit set. Then output of this comparator will trigger LM555 RS-Flipflop to reset.
Using the NE555 and LM311 give several improvements :
1. Guaranteed ON/OFF condition. 2. No flickering output. 3. Avoid forcing Switch to ON state when overcurrent is detected. 4. When overcurrent is detected, the switch will stay OFF. 5. Indicator ON and FAULT condition
The finished (still prototype) picture :
Front View
Rear View
Comments