Teardown Tuesday: Dewalt USB Power Supply - LEKULE BLOG


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Friday, 11 March 2016

Teardown Tuesday: Dewalt USB Power Supply

This week we're going to take a look at what makes the Dewalt DCB090 USB power source work.

The Dewalt DCB090 Power Source

This is a relatively small device, made by Dewalt, that attaches to the top of their 12v Max  and 20v Max batteries. The Dewalt power supply has 2 USB ports and a 12V output that is used in applications such as in Dewalt's Heated Jackets. Opening the power supply reveals a single circuit board and a proprietary connector. For being a power supply there are a lot of components packed inside. Let's take a look at what they all do!

The power source opened to display the electronics


Power Connector

This connector connects to a Dewalt Battery

The large 8 pin connector is the primary power connection for between the battery pack to the power supply. Out of all the pins, only three are connected. The wires are directly soldered to the connector. Connecting the wires to the circuit board are stress relieving crimped on connectors.

Crimped on wire stress relievers


Potting Compound

The white potting compound surrounding the inductors  

Looking at the circuit board one of the first 'components' that is viable is the large quantity of potting compound around the larger components and at the edge of the circuit board. This adhesive is used to reduce the effects of shock and vibration on the components. For the rest of this teardown, the potting compound was removed.


The 'brains', a PIC microcontroller! 

At the heart of this device is a Microchip PIC microcontroller! The particular IC is the PIC16F506, this is an 8-bit microcontroller that can run up to 20MHz and contains 1.5k of program storage. A large benefit of this particular processor is the price, in quantity, it can be below $0.60 each. In comparison, an Atmel Attiny85 is $1.17 in the same quantity.


Voltage Regulation

The Dewalt USB power supply uses has two separate switching DC-DC converters and a linear one. The first DC-DC converter used is the TI TPS40200. The TPS40200 is a buck controller rather than a buck regulator meaning that it does not contain a switching fet internally. The TPS40200 is part of the 5v power supply.

The boost controller for the 5v output 

For the 12v power supply, the Dewalt Power Supply uses a Noveltek NT3875A. This is a step-down regulator that provides current limiting. On the PCB there is also a 0.2 ohm current sensing resistor.

The Noveltek voltage regulator for the 12v output of the power source 

Also part of the power supply are the two inductors. There is a 47uH inductor attached to the 12v power supply and a 33uH inductor on the 5v power supply.

The two large surface mount inductors can be seen 

Finally, a third small voltage regulator can be found for powering the microcontroller. This is a Ti LP2950, 5v, low dropout (LDO) regulator that can supply 100mA.

The linear 5v regulator to power the microcontroller 



The top of the circuit board 

Also contained in this device are a handful of power MOSFETS, diodes and caps to assist in the DC-DC conversion. For a MSRP of $30 this power supply certainly isn’t cheap, but it is built well. The Dewalt USB power supply is a fairly robust power supply name brand components and potting compound. While this is not waterproof this higher build quality than other USB power supplies. This product contains two switching DC-DC converters that typically aren’t seen with such a high power rating. Dewalt has a reputation of making relatively rugged and quality tools, this USB power source follows suit!

The bottom of the circuit board 

Thanks for looksing at this week's Teardown Tuesday.  Stop by next Tuesday for another teardown! 
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