How to increase DC voltage drop?

[John_Nash]

Hello everyone,

I met a problem that is about current load of a charging device,
the charger is able to supply 1.5A charging current, but the drop of DC is too much when the loading is equal to 1.5A ,
please see the table below:
_________________________
VDC Load
5.05V 0mA
4.95V 500mA
4.69V 1500mA
_________________________

If I need to increase the VDC to 4.8V at 1500mA load, how can I do?
(Note: this is a USB charger)

Thanks a lot,
John Nash

 

[barry]

You say your charger is able to supply 1.5A. BUT is your charger capable of supply 1.5A at 4.8V? It looks like can't. You can't create power out of thin air. Get a different charger, or redesign the one you have.

 

[John_Nash]

Sorry I say clearly , my charger is able to supply 1.5A, but the drop of VDC is too much (4.69V at 1.5A), I hope that my VDC is above 4.8V when the load is 1.5A.
How can I do for reducing VDC drop?

Thanks,

 

[barry]

As I said, your charger is inadequate. You can't magically make it put out more than it's capable of unless you redesign it.

 

[John_Nash]

I know, but I am just design for USB protocol part, and don't know how to design Power part,
so I need more opinions to study technique of power design.
Thanks,

 

[BradtheRad]

Your 5V power supply has an effective internal resistance of 0.2 ohms. (I figured this out using a bit of math, and with the help of a simulator.)

Some of it may be ohmic resistance, and some of it may be in the form of switching reactances.

This internal resistance accounts for the voltage drop when you attach various loads.

To get 1.5A at 4.8V, you would need to open up the supply and fiddle with it.

It would not be easy to reduce the internal resistance directly. However it's possible you could raise the output voltage, if you find the right component to fiddle with.

 

[BabaYaga]

@John_Nash,
I don't know what your charger internally looks like, but lets say its an AC to DC Charger then it will be something like this,
Step-down Transformer --> Rectifier --> Filter --> Voltage Regulator
Now if your charger is rated for 5V@1.5A reading then at peak current your output voltage will drop due to resistance as @BradtheRad has above stated, this is basically called as Drop Out, supposing that you can't fiddle with your charger internals only way to get 5V would be using 2 chargers and connecting them in parallel, this would increase the current rating by 3A, and since your current requirements is just 1.5A, the voltage will not drop and you will get required output of 5V.

Only problem is you require now 2 chargers.
I Hope this helps.

 

[electronic_satya]

only way to get 5V would be using 2 chargers and connecting them in parallel, this would increase the current rating by 3A, and since your current requirements is just 1.5A, the voltage will not drop and you will get required output of 5V.

I am really not sure if we can connect two power sources in parallel, i heard of connecting power sources in series. could someone please clarify my doubt?

thanks and regards

 

[barry]

Connecting two power supplies in parallel will increase the available current. This means each supply would only have to supply half the load current, and those would gave half as much IR drop. But this is not an ideal solution.

 

[BabaYaga]

Connecting 2 power sources just like that, would not be recommended, but you can do so by providing some protection circuits like a short circuit protection, or use zener diodes etc., given the conditions that you have provided i suggested this might be the solution, further i would suggest you to open up your charger and look into it to find what regulator he is using as a lot of manufacturers suggest circuits to increase the current capacity of the regulator, then in that case you can easily connect your charger outputs by the suggested circuitry and meet your requirements.

Bottom Line - open up your charger, look what regulator he is using, look into the datasheet of the regulator and you might get answers to your question.
and if you do find what regulator is inside please post here.