DIY Overcurrent Protection for DIY Power supply Using OLD PC PSU. - Page 1
Forum section: electronics / projects

author: volcano_dragon
author_rank: Newbie
timestamp: June 11, 2025, 10:53:13 am
content: Hey everyone! 👋I've built a modified version of the overcurrent protection circuit from GreatScott’s awesome video:https://youtu.be/7ctPSgaLxbc?si=IU6TsLC7SzzVlQCSI wanted to adapt it specifically for ATX power supply control using the green PS_ON wire, with added features like latching, delayed shutdown, and controlled PSU restart. I'm sharing my Falstad circuit image below and would appreciate any advice or feedback before I build the real thing.My Goals:Detect overcurrent using a shunt resistor + op-amp for differential voltage amplificationUse a comparator to trigger a shutdown if current exceeds a defined thresholdControl PS_ON (green wire) of an ATX PSU via transistor switchAdd Transistor B to disable PS_ON line by grounding it when overcurrent occursAdd Transistor C (PNP) to latch Transistor B ON, preventing restartAdd an RC delay circuit to slow down the turn-off of Transistor B (avoid rapid toggling or relay chatter)Power logic entirely from 5V standby rail of the PSU (always-on line)I don't want to use relay, because they degrade over time.How the Circuit Works (in brief):1. Normal Operation:Shunt resistor voltage is amplified by an op-ampComparator compares this to a reference thresholdAs long as current is safe, Transistor A keeps PS_ON grounded → PSU stays ON2. Overcurrent Detected:Amplified voltage exceeds comparator thresholdComparator output goes HIGH → turns ON Transistor BTransistor B pulls down base of Transistor A → PSU shuts OFFTransistor C (PNP) latches B ON so the fault holds3. RC Delay:Base of Transistor B is charged through a capacitor to delay shutdown release (currently tuned for ~5 sec)4. Manual Reset (optional in next step):Planning to add a push-button to reset the latch and restore powerFeatures Added vs GreatScott Original:ATX PSU compatibility (via green wire PS_ON control)Latch mechanism using PNP transistor to hold shutdown after overcurrentDelay circuit on B’s base using capacitor + resistor for smoother shutdownPowered entirely by 5V standby (no external logic supply needed)Looking for Feedback On:Component tuning (RC delay, latching resistor values)Any edge cases I might’ve missed (like noise, startup behavior)Safer/better alternatives to transistor latching?Would you suggest switching to a logic-level MOSFET or comparator IC like LM393?PFA Falstad Screenshot of Circuit.Thanks in advance 🙏Happy to share the Falstad text file if anyone wants to simulate it too!

author: volcano_dragon
author_rank: Newbie
timestamp: June 11, 2025, 11:07:34 am
content: Falstad Link : (https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWc0EDYAsAmVBmMAOfdA-MAdkxAQiQUioFMBaMMAKABcQcFL05umev3r0Io8AIAmDAGYBDAK4AbDpxDoMVMHxyVqlMVGNhpcparYB3QcLCpbVTPihsA5tyIgyqFzi-4AqLWjrx+Qt6+rjb+6JHh9D4ukCHoek4uaZRJ0RrpObHxrgBOGloGGdqGknBspXr0hQ3ckHFi8Gz2lM2Y-I44rSCUMgoqHEzKDFLgxqKw7ABKGgCcDkxa6KsgTFsSfUgSMAipW+txzWe5F1o9fSmlWRoCjwNtNSk2L4OPlx95lJdNmstCkAB7bexDfAOXoQZzLDRDegABQAygB9ADyADkADoAZwAFABxYoMBgAOwJAHUAJZkgCUBIA9rICWiAKpsJY7GF9XngHyzJ5UYVHEKQ14gG6DFLkFySnBrQLcJXgOLiaDVGCQJCmeBBWCUCI6sAHWCQcRsaaQzBobYqu0wkAjCxqGxMR32z2NWUSmH2yV+j1bXr0AVSv4RwY+lptCVCqWYChx3LJ7peZqFFJLRUOG5qvZibVQFAhGUaxPBh2NCIRk1sHBkcNbC5bYgOHCzOrbduQgUVObsUoDnS9-OQZJDaDoNgABwhQo7i4cFS7En1BqjYHQcQqo8MIRYu40-b7DijW1Qk-HRUvDhyYbvR53cWXLCXkO3J-35FXY-ubZND3a9tiVFw0AkOhag9cCNBVJg4MgkowIiXcXCYJ0NHQKdNx7RC0Jw1D6DCYxoKjLD0JXU8LyPOCqII4QiKjZpSMY7wvBYiIyC8AUePjEMH14rYcm3IV9yw5DAMw+1kMQqIpPeecgPKZxiMqdcTC3GCVLfLQmGAyoo0MtiTNAlJ+AReTMn0wzDPXaALwtTVIEwPBtI8w8PWXH4fKCI8-PDHRMn8j1gqeIK1OaYzISBIDIX43IDIS3jmkSv4nz-IZ9nMkInwKbiomMjZbK0EEArKuIVXKmxWABIjTOSEJSPSFq-XIOIWAcLKtCyiBN1LJAFgYfFaXxDh5ApABjBgJTUrLMqFP50nsWsQF2EJ0i2cKNtqtTtrU5jlJ27r5sTYVNwNF8orrVsGxsFU+rO2iF2qqqxHOjcPJCdsXCveN5HAMciLqoCXAgrStwurcfvzd7pXjcFMLNaUqEtdbEQiABhZkAFs53kYp5A4ZligJWRSYJfErFpDgpoAC1pCk3AJDh6YYAkABUiYpUbxsp-EACEqeZVn6eJglhuUeQAE8CUJeQpo4RR5GUZQ5fxTkmXxKbJoJAAjDn8VZWQ2HBAhtDIDRkycYRwARbnJvxaACWFokOXxKZyYFqbmQpDhimZNWmZZ8b2a5nnnYJABBV35E9hkzaBkKEQGTJgaREBHd5l38VjokKbJzWMRxROkc0CDliC0CEGWLs4giTE5yYaP8YJAAxAWADUg9zgARWlZFkXPW7nZRB9pXWOFpP2k8w1AkGcCAWF1KE33ABwpdlgl453nelZV5R2VRLkbCfZD8qKl9uqFLrthqiFgXOOsH8MnJHlE5q1IMiCbtyNq9yHXSCkLgCAlzpAwMIYBEJob0FdGME4T8EbhgfpA++cQ0E8EPKUTBvBkE0UhikaYjwRD-BWM6eBlgYh4NISQ0KZC4p2V2mUN87YNjANSOw-Q4CvL4NIiZNSfwBE2T3ABNgU1KioF6JUCobQLTwGWIopRyiVEIh1OjdRVobCkSkYAlwn9tFqXfloT++J8FUTQaRCQChlCex7Pw1qalBxozBBoFMPB6DLDHDweu4AXDZyjviLG8tkTYmRNrQkHsvb4kLgSaWdNGbMzFkbfW8cjasgjk7XOgsy4OkruGfQddERgARAAGWZPIKQksRrQDnvgeuCAuwOHQPaDULhUT00UP7apzsk44GWIUpAPhaDLEyH4kAWN5BzlzoSRQnsqkxNFviSpUgQ4EhkNLDWTMCSYnbu3FkbJ8QBOybkugVkyAQFQMsJA6wxkRAQAAN2PhyAkqIJoUikPrDWmIAD0yIk4LyQHFMgCBWEIkrCAYansOCvJpgkns6ZUyIuzDUNgQA)