- #1
How can I add overload protection to my current limit circuit?
- Thread starter mariuszoll
- Start date
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- Protection
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Discussion Overview
The discussion centers around enhancing a current limit protection circuit to include overload protection, specifically focusing on how to switch off a MOSFET when the load current exceeds 1A. Participants explore various approaches and clarify the workings of the existing circuit.
Discussion Character
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- One participant describes their current limit protection circuit, explaining how it operates with a transistor and resistors to maintain a current limit of 1A.
- Another participant questions the definition of overload protection and its distinction from the existing current limit feature.
- Some participants suggest that the current circuit already provides effective overload protection, while others seek clarification on whether a complete shutdown is desired.
- A later reply proposes using a "latched overcurrent fault detector" with a latching comparator to turn off the FET when the current exceeds the limit, referencing external articles for further information.
- One participant expresses interest in achieving similar functionality with discrete components and shares an attachment of their circuit attempt, indicating challenges in implementation.
Areas of Agreement / Disagreement
Participants express differing views on whether the existing circuit already provides sufficient overload protection, and there is no consensus on the best approach to implement additional shutdown features.
Contextual Notes
Some participants mention the need for clearer definitions of overload protection and the specific conditions that should trigger a shutdown, indicating that assumptions may vary among contributors.
- #2
gnurf
- 370
- 8
Can you explain how the current limit protection circuit works?mariuszoll said:
- #3
mariuszoll
- 5
- 0
Hi,
under normal conditions transistor Q1 is blocked. R2 is used to sense the current through it. When current is 1A, the voltage drop over R2 is 0.7V and Q1 is turned on, which in turns increase the voltage on the gate of M1, and keep it at the limit of conduction.
R4 is used to limit the Q1 base current in case of a load short circuit.
R1 allows M1 to turn on and pass the voltage and current to the load.
And thus, the current limitation is made.
under normal conditions transistor Q1 is blocked. R2 is used to sense the current through it. When current is 1A, the voltage drop over R2 is 0.7V and Q1 is turned on, which in turns increase the voltage on the gate of M1, and keep it at the limit of conduction.
R4 is used to limit the Q1 base current in case of a load short circuit.
R1 allows M1 to turn on and pass the voltage and current to the load.
And thus, the current limitation is made.
- #4
gnurf
- 370
- 8
What do you mean by overload protection and how is it different from what you already have?
- #5
skeptic2
- 1,776
- 60
I agree with gnurf. It looks like you already have a pretty effective overload protection circuit. What more do you want? Do you want it to shut down completely at some point? If so you have to define what it is that should cause the circuit to shut down.
- #6
mariuszoll
- 5
- 0
Hi,
Beside this current limitation, I would like also, to shut down the circuit when current becomes equal or higher than 1A.
If you could give me some ideas how to do it, I would appreciate it.
Thank you
Beside this current limitation, I would like also, to shut down the circuit when current becomes equal or higher than 1A.
If you could give me some ideas how to do it, I would appreciate it.
Thank you
- #7
gnurf
- 370
- 8
I think you're looking for a "latched overcurrent fault detector". In the article linked to below they use a latching comparator that turns off the FET when the current exceeds the limit. Hopefully that might give you some ideas!mariuszoll said:
http://powerelectronics.com/mag/510PET07.pdf
http://www.maximintegrated.com/datasheet/index.mvp/id/2204
Last edited by a moderator:
- #8
mariuszoll
- 5
- 0
Hi gnurf,
Thank you for the articles, they are very good. Do you know how I can do the same thing but with discrete components?
I tried to improve the previous circuit, in order to switch off the mosfet, but without good results. You can find attached the circuit.
Thank you
Thank you for the articles, they are very good. Do you know how I can do the same thing but with discrete components?
I tried to improve the previous circuit, in order to switch off the mosfet, but without good results. You can find attached the circuit.
Thank you
- #9
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