# Best way to convert 48v DC to 7.2 v DC

#### Kmoreau893

Joined Jan 26, 2007
1
I have been using a Sony Bluetooth Microphone and Receiver system

(http://www.sonystyle.com/is-bin/INT...Name=acc_DIAccessories_DICamcorderMicrophones )

with my Sony Camcorder with a proprietary connector that supplies power and audio inputs from the camcorder (called an Active Interface Shoe-AIS).

I recently purchased a more professional Sony Camcorder with XLR audio (the Sony HVR-v1U) which doesn't have the Active Interface Shoe, but does have XLR inputs with 48v phantom power. I want to try to use the bluetooth receiver with my new Pro camcorder.

The bluetooth receiver is powered by 7.2 volts. I've performed the custom wiring and I can get it to work well stand-alone with a 7.2v battery. I measured the current draw when operating the bluetooth receiver and it is 65 milliamps.

With a simple voltage divider circuit using a 630 ohm and 110 ohm resistor I can get the 48v down to 7.2 volts to power the bluetooth receiver. However, I'm afraid I'm losing a lot of power with 3w of power dissipation and heat, which will drain the camcorder battery quite quickly.

Is there a simple way for me to reduce this voltage without wasting precious camcorder battery power unncessarily?

-Keith

#### mrmeval

Joined Jun 30, 2006
833

#### Papabravo

Joined Feb 24, 2006
15,560
http://www.national.com/ds/LM/LM117HV.pdf

Eh, I won't say it isn't wasteful. If you want hyper efficient try nationals search engine for a buck/switching regulator.
The power dissipated by the linear regulator will be
Rich (BB code):
(48 - 7.2) * Current

For 25 mA of current this is 1 Watt
For 50 mA of current this is 2 Watts
You will need a substantial heatsink

The only rational solution is a switching regulator in the buck configuration. The efficiency should be in the 80% to 90% range. Linear Technology has a simulation program that will give you canned designs from your input and output voltage and current requirements.