How to bring down 5vdc to 4vdc without using regulators?

[ME]

Re: 5vdc to 4vdc?

@Tornado:

how can i know the voltage drop of a certain schottky diode? like MBR0250L for example?

Look in the data sheet for the diode.
You can search for data sheets from all manufactures at this great site: **broken link removed**
If you know the manufacturer you can go directly to their site and download the data sheet.
The voltage drop across different schottky diodes is almost the same, normally around 0.3 - 0.4 V.

I couldn't find MBR0250L, maybe you mean MBR0520L?
Here are some specifications from Fairchilds data sheet for MBR0520L:
Forward voltage @ 100 mA, 25 °C: 300 mV
Forward voltage @ 100 mA, 100 °C: 220 mV
Forward voltage @ 500 mA, 25 °C: 385 mV
Forward voltage @ 500 mA, 100 °C: 330 mV

Specification for 1N4001:
Forward Voltage @ 1.0 A, 25 °C: 1.1 V

 

[iDk]

Re: 5vdc to 4vdc?

@ME:
sorry for the mistake. i do mean MBR0520L. i already downloaded the datasheet before i posted here but somewhat i can't locate in the datasheet the voltage drop for MBR0520L so i decide to ask for help in here...

thanks again and regards.

 

[ME]

If you look in the MBR0520L data sheet from Fairchild you can easily find the forward voltage. Just look under Electrical Characteristics or at Figure 1. Forward Voltage Characteristics:
https://www.fairchildsemi.com/ds/MB/MBR0520L.pdf

 

[iDk]

@ME:

so it mean that in MBR0520L the voltage drop is 300mV in the given data below?

Forward voltage @ 100 mA, 25 °C: 300 mV

is it just ok if i use this diode instead of 1N4001?

 

[jzo777n]

Re: 5vdc to 4vdc?

iDk wrote:
>hi. i have just tried to read some notes on the manual of the mobile
>phone. the maximum battery voltage is 5.4vdc. my decision on dropping
>the 5vdc usb supply voltage to 4vdc is in order for me in safe limit
>because the normal battery rating of mobile phone like nokia is 3.6vdc.
>and also i saw on the schematic of a dongle which is being powered thru
>USB the positive side they put in series a 1A diode (1N4001 i think?)
>then this will serve as a power supply of the mobile phone. is that safe
>enough for a mobile phone just by putting a 1A diode in series?

I think you have missed something.
You must differ between nominal voltage (or max discharge voltage) and charge voltage.
If you want to charge a Lithium Ion, the max charge voltage is 4.2Vdc and
max nominal is 3.7Vdc (older type 3.6Vdc)
If you want to charge a Ni-MH battery, the max charge voltage is about 1.5Vdc
for a cell (with 3 cells, 4.5Vdc) and max nominal is 1.2Vdc (3.6Vdc/3 cells)

And above that you need some headroom (dropout voltage) for the charger if its a linear type.
So for a Lithium Ion charger you probably need min 4.5Vdc supply and slightly more for a Ni-MH.
If its a switching charger, the supply voltage depends of the type.

I presume also that you are going to supply the charger in the mobile and not try to feed the battery directly.
Because then you must built a charger and that’s is something completely different.
If you want to learn more about battery try to look at different manufactures, for ex. Panasonic https://www.panasonic.com/industrial/battery/oem/

 

[iDk]

@jzo777n:

thanks for tha info but i'm asking about on how to bring down the 5vdc usb supply to 4vdc. and i'm not intending this for charging the mobile phone battery. i will be using this to power up the phone without battery...

anyway thanks again for the info.

 

[sisc1525]

LDO is used widely nowadays.you can find it at the company such as AD MICREL NATIONAL ....

 

[eladg]

Re: 5vdc to 4vdc?

hi. whats the best thing should i do to bring down the 5vdc (USB supply) to 4vdc without using any regulators, just by using only discrete components?

thanks.

what current is at the line ?

 

[MRV]

Re: 5vdc to 4vdc?

Just use resistors I have used it to convert from 5V to 3.3V