| Electronics > Beginners |
| Simplest circuit possible that should trigger above 4.5V |
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| mitrynicolae:
Hi everyone, Does any of you have any suggestion about a circuit that should trigger on a voltage above 4.5V but bellow or equal to 5V? The specs are as follows: - the if the input voltage is bellow 4.5V the output should be disconnected - if the input voltage is >4.5 but <= 5V then the output should be connected to ground - the circuit should be as simple and as cheap as possible. For example using a simple transistor is does not do the job because if the voltage will be above 0.7V the transistor will conduct which broke the requirements. If we will use a comparator for this job then we will also need a 4.5V refference and also an output transistor since the comparator cannot source sufficient current which complicates the circuit. P.s. Please note that 4.5V is just a wish not a solid requirement. If the suggested design work at 4.4V or 4.6V that is good enough. In fact any voltage that is above 4V is good enough. As a little background, I have a pin of the MCU that is connected to an optocoupler. If the optocoupler is on then the output will be around 3.5V If it is off then the output will be 0V. In the same time the pin of the MCU can be set to output instead of input. In this case it will output 5V. The idea is that ONLY the MCU should trigger the above schematic and not the optocoupler. The optocoupler should only inform the MCU that something is changed. Thank you |
| mariush:
honestly, a couple resistors and a 6-8pin micro would do the job. ex a pic10f320 .. set internal vref to 2.048v or 4.096v and use 2 resistors to divide input by 2-5x to be below max vref. |
| AndersJ:
Use a voltage supervisor normally used to reset microprocessors. |
| strawberry:
window comparator |
| soldar:
mitrynicolae, I want to thank you for a question well presented and detailed. You can try this simple circuit and it should be easy to adjust the voltage. Let us know if you have any questions. Edit: Should be 1K5 instead of 1K2 Ohm. You can adjust it. This will have a gradual switch as the voltage increases. If you need a sudden switch then you need a Schmit trigger. |
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