Hi all,
I am a mechatronics engineer trying to learn and get into electrical stuff. I have attached the circuit that i currently have. Need someone to point out changes/mistakes that i have made as it does not work.
What I am trying to achieve:
Once i connect my android phone to charger, I want it to have a 1-2sec delay before it sees the power and starts charging.
General info:
Phone needs 5v and 500ma to charge. Phone has its own charging circuit which pulls current as it requires as long as it is connected to a 5v source and the source can provide the required current.

Please assume T1 is a darlington transistor - NTE64.

The RC circuit by itself works fine. It gets to 1.2V in about a 1sec, which is what is required at the base of darlington transistor to activate.


Appreciate all the help here.

 

What is the issue? You seem to be saying something doesn't work but you don't say what.

 

What is the issue? You seem to be saying something doesn't work but you don't say what.

The phone does not get 5v or 500mA. Current is either 0 or very small that my multimeter does not measure.

 

A darlington will have about 0.7 volts collector to emitter when it is on. It may be that the phone interprets this as being an overloaded or out of tolerance supply and won't charge.

You could use a "logic level" FET instead of a darlington. The delay will be somewhat less predictable because the threshold voltage of the FET is not tightly controlled, but the ON voltage of the FET can be very low depending on the FET used - under 20 mV would be no problem with an inexpensive FET.

 

I need to look into FET. Can you suggest part number or something as i am not too electrically inclined.
I ran few more simulation and results are just not making sense to me at all.


Should the voltage across resistor always be approx. 5V and current should be 5v/R? I do not know what why the results are the way they are. There is something going on that i do not understand.

 

Clarification: This is what i want ideally, but want a cheaper/ physically smaller solution than a relay.

SW1 0 is a relay that gets turned on when the voltage reaches 5v. Capacitor takes 1 second to reach 5v and resulting in me getting a 1 second delay. How can i achieve this using cheaper and smaller component?

 

Anyone has inputs on if this circuit would work or not? and if any changes/improvements i should make. Keep in mind i need 5v and 500mA at phone.

 

Anyone has inputs on if this circuit would work or not? and if any changes/improvements i should make. Keep in mind i need 5v and 500mA at phone.
View attachment 148486

That circuit won't work with that transistor. Its threshold voltage is too high as shown here:


It will not have its minimum on-voltage when switching 1/2A with 5V Vgs, as can be seen below.
You need a logic-level MOSFET with a Vgs(th) of no more than about 2V max. as ebp stated.

Then the circuit should work, although you may have to adjust the RC values to get the desired delay.

 

That circuit won't work with that transistor. Its threshold voltage is too high as shown here:
View attachment 148490

It will not have its minimum on-voltage when switching 1/2A with 5V Vgs, as can be seen below.
You need a logic-level MOSFET with a Vgs(th) of no more than about 2V max. as ebp stated.

Then the circuit should work, although you may have to adjust the RC values to get the desired delay.

View attachment 148489

@crutschow - Do you think this would work? https://www.digikey.ca/product-detail/en/rohm-semiconductor/US6J2TR/US6J2TR-ND/721537

 

@crutschow - Do you think this would work? https://www.digikey.ca/product-detail/en/rohm-semiconductor/US6J2TR/US6J2TR-ND/721537

That's a dual MOSFET, which you don't need.
One like this should work.

 

Returning to your circuits at #5: What do your results tell you about the current gain of the transistor in the model?

 

@crutschow - Thank you for the help. I am new to electronics so forgive me noobness.
@ebp - I do not understand your question. Would you kindly rephrase it?