# Create External long term and Efficient Power Supply for Wireless Temperature Sensor

#### ronbo76

Joined Apr 2, 2018
20
I want to make the power supply in which need to send the output of 20mA current which is provided to my wireless temperature sensor, I am using 9v battery cell.

I don't have much good knowledge about current amplification so I was thinking to start with Transistor circuit for current amplification.
I need some advice about how much minimum input current, I have to give to the transistor via 9v DC battery so that I will be able to achieve around 20mA output.

Any circuit suggestion or any theoretical explanation will be a great help to me.

Note: The sensor also has the standard version in which they provide the external power for input, which I am using with my storage containers.

Joined Mar 10, 2018
3,793
Not clear what you are trying to do.

Can you hand draw a simple block diagram of sources and loads,
labeled with voltage and current ?

Regards, Dana.

#### ericgibbs

Joined Jan 29, 2010
9,361
hi robo,
The datasheet for the wireless temperature sensor states
Up to 500,000 Transmissions from 2 AA Batteries

E

#### ScottWang

Joined Aug 23, 2012
6,860

#### ronbo76

Joined Apr 2, 2018
20
Hi,
First of all thanks for the reply, In this Wireless Temperature sensor, 2 AA batteries are used

but-but-but!!

They also give the optional external power adapter option, And I want to design the 9v battery power source to connect it with optional power and send minimum current input which amplified and send the 20mA output to the circuit they are using. I just need some basic suggestion is it possible?
Any useful circuit design and leads to make this kind of power circuit work will be much helpful.

#### ericgibbs

Joined Jan 29, 2010
9,361
Morning ronbo,
The minimum 20mA current value on its own does not give enough information for us to make a helpful suggestion.
Is there a voltage range stated ? ie: 6Vdc thru 9Vdc
E

#### ScottWang

Joined Aug 23, 2012
6,860
The easy way is that you can use a 78L33 (3.3V/100mA) voltage regulator and two schottky diodes to connected 78L33 and the 2 AA batteries together, you can buy an adapter like 9V/100mA, the Vf (forward voltage) of Schottky diode about 0.3~0.4V, I can't make sure the working voltage range of sensor, if the sensor could working lower than 3V then the circuit shown below will be works, normally you don't have to limits the current, the sensor will be draw only what it needed.

#### ronbo76

Joined Apr 2, 2018
20
Hi, Thnks for your circuit suggestion,
Can I also use ULN2803 for current amplification?

I have used it with 7 Segment Display and it was working fine with it. So can I use the same IC, For my circuit to draw more current from the power supply?

#### ScottWang

Joined Aug 23, 2012
6,860
What's the load (V/I) for ULN2803 (500 mA)?
Maybe you can use 2SC1384(1A) to drive the load.