Voltage Controlled Switches?

[Smitty]

Hello,

I'm new this forum. I was wondering if there is such a IC in which if the input voltage is greater than or equal to 5V the switch will close and allow current and voltage to flow through. And on the other side if the switch is less than 5V then the switch is open. This would be ideal if someone can lead me in the right direction.

If there isn't such a switch I was thinking about about using a compartor, but I haven't gotten that far in the design.

Thank you for your time.

 

[ronv]

Sometimes it is easier to explain what you are trying to do. But having said that a zener diode might do what you want.

 

[KeepItSimpleStupid]

Explaining what you want will bring up a bunch of ideas I'm sure. Any switch should have some hysteresis e.g. on at 5 off at 4.9. The expected currents would help too. Right now, I am thinking signal level.

There is a limiter OP amp that does some really neat things. You set a high and low limit and anything above the high limit is output as the high limit and anything below the low limit is set a the low limit. It's a dual supply and high bandwidth OP amp.

 

[ChrisP58]

A voltage comparator driving a p-channel mosfet should work.

Feed the (-) input of the comparator with a 2:1 divider from the +5 input. Feed the (+) input through a resistor with a 2.5V ref from a TL431. Add another resistor from the (+) input to the output to provide a bit of hysteresis like k.i.s.s. suggested.

 

[Smitty]

Ok great. So what I'm actually trying to do to create a solar power charger with a usb output. My inputs are my solar panel and battery. The solar panel is connected to a buck/booster converter then to charge controller and then to the battery. I'm using a 12 Volt battery. What I'm having trouble with is figuring out how to control the flow.

Here is a quick diagram with the conditions I put together.
https://i.imgur.com/IOcl1rb.jpg

Can you now see why I'm in need of a switch? Let me know what you guys think. I'll check this often to check for replies.

 

[Smitty]

I forgot to add that since the spec for usb charge is 5V i will be using a voltage regulator of 5V but the switch will go before the voltage regulator.

 

[KeepItSimpleStupid]

So, then why don't you just use a buck converter to 5V from the battery with a low voltage cut out?

You may not be able to charge more than 100 mA without adding a charge port chip or a special cable with 2 resistors (Motorola, for instance)

 

[tomizett]

I agree with the above. I think the thing to do would be simply to trickle charge the battery from the solar cells (looks like you have all the kit in place the do that already) and then simply drop to 5v to the USB output - no switching at all required, the batteries are simply on-line all the time.
When the available power from the sun exceeds the drain on the USB, the batteries will charge - in the opposite case, they'll discharge. If you've a proper charge controller it will prevent over charge/discharge etc.
If you can stand the additional complexity, a switching step-down regulator would be more efficient and make better use of your free energy, given the large drop from 12v at 5v.
Hope this helps.

 

[Smitty]

Thank you all for your help. I think I didn't explain this enough. What I'm trying to create is a portable charge controller. I have already designed a buck/boost converter in which I will be using a small arduino to power the converters. (Yes, I'm using a small external battery to power the arduino.)

As far as a comparator goes I'm trying to think a essentially a simply way to solve my problem. A comparator would involve an external source to power it. I'm thinking that a voltage regulator (5V regulator) can simply act as a switch. The problem I'm having figuring out if the voltage is under 5V will the voltage regulator still draw current to it or does it not.

Also if you refer to the picture I attached to my last post. I need to figure out a way in which to power the usb. How can I combine the two separate outputs to one? My one friends suggested to use a OR gate but again I can't figure out how to implement it to actually circuitry. Ideally, for each situation I listed I want to be able to control it, not letting the environment in control it.

 

[KeepItSimpleStupid]

Well, diodes would allow the highest voltage to go through. I know, not what you want.

What is the max voltage and max current encountered?

 

[Smitty]

The max from my solar panel I have in 12V, 200mA. To power up a USB I need 5 V, 200mA. Also, I need to run power to the charge controller but I'm not exact sure if what I projecting is right. If you're having trouble understanding me let me know. I can write up my design and upload it. It might be easier to see and understand why I need a good switch and where I might run into a problem.

 

[KeepItSimpleStupid]

The standard practice is charge controller controls battery and prevents overcharge. May include MPPT.

MPPT can mean a lot here. Perturb and measure is one method. This changes the operating voltage of the panel to highest power from array and boosts or converts it to an intermediary voltage or to the charging voltage.

Then if delivery is at 5V step down converter from the battery does this. Low voltage disonnect is enabled here.

Even if you generated 2A at 5V USB cant use it. There is current handshaking that takes place otherwise your limited to 100 mA.