Do You Need a Power Supply or a Battery Charger?

Custom Battery Charger

The terms “Power Supply” and “Battery Charger” are often used interchangeably, but they perform distinct functions.

A power supply is designed to supply a constant voltage to a load. As the load requirements change, it continues to supply a fixed DC level.

A true battery charger generally supplies a regulated current, first to charge the battery, and then switches to a regulated voltage mode. This is specifically required for Li-Ion chemistry where overcharging is not only damaging to the battery cells, but can also pose a possible fire hazard. A smart battery charger will not only never overcharge cells, but can also monitor battery temperature, switching off a fast charge when certain parameters are exceeded.

A power supply used as a charger cannot do this, and will continue to pump energy into a battery regardless of its condition; fully charged, battery fault, or shorted cells.

In order to achieve maximum battery service life, a properly designed charger should always be used to charge cells.

How Is My Power Supply Grounded?

Grounding Pic (Reduced size)

There are generally two standard configurations when it comes to grounding in a switching power supply.
One method for a normal three wire line input is having the AC ground connected only to the inlet ground terminal.  In this method, there is no connection to the output ground, or DC return, and is considered a “floating” AC ground.

The second method is to have the AC ground wired to the DC return.  This connection has the added benefit of ensuring that the output ground is at the same potential as the input ground, so there is no possibility of any shock hazard.

For a linear supply using a laminated transformer, there are three common grounding methods:

  1. The AC ground can be connected both to the transformer core and output ground terminal, or the DC return.
  1. The AC ground can connect only to the transformer core.
  1. The AC ground can be carried through directly to a separate output ground lead.

The choice of grounding methods is often dictated by customer system requirements, and in some cases supply design topologies.

LED Drivers: Constant Current or Constant Voltage Requirements

LED Dark (reduced)

In order for typical LEDs to work, they require a DC voltage source.  Depending upon how many LEDs are being powered and how they are wired, they will best employ either a constant voltage or constant current supply.

LED arrays with a built-in driver module will only need a constant voltage supply, which delivers a fixed output voltage at any current load up to its maximum rating.  Other than application-specific packaging, such as moisture resistance or water proofing, these are ordinary switching power supplies.

LED arrays consisting of multiple strings may require a constant current driver which talks directly to the LED strings.  In these, the output current is fixed, instead of the voltage.  As the current drawn by the LEDs change, the output voltage will vary, within a preselected min-max voltage range.

Specifying Reliable Output Connectors

Connector HDR (Reduced)

There are many styles of output connectors used in today’s power supplies.
Two of the most commonly used output connectors are the female barrel and male DIN. They are economical, widely available, and a good choice for many power supplies.  However, there is a tendency to use them in applications which exceed the contact ratings.

For example, the female barrel has a generally accepted maximum rating of 5 Amps, yet they seem to appear on supplies rated up to 10 Amps.  Running the connector at this current will eventually cause damage to the contact area, or to the overmold, due to heat issues. So for maximum reliability, we recommend no more than 5 Amps.

The male DIN connector is another popular style, and is available with 3 – 8 contacts which are rated for 3 Amps maximum per contact.  Typically, on a single output supply, two or three of the contacts are wired to the positive output, and the remaining contacts are wired to the AC ground, DC Return and shell.  This distributes the current between all the contacts so the 3 Amps maximum is not exceeded.

When higher output power is required, we recommend the power Mini-DIN connector, which is available in three and four contact versions, and have a 7.5 Amps maximum rating.

Another widely used connector is the locking Molex, which can be supplied with contact ratings up to 12 Amps.

In summary, a conservative approach when choosing an output connector will pay dividends in providing long and reliable power supply operation.


Rohs to Rohs 2

RoHS, a directive by the European Union which restricts the hazardous materials found in electrical and electronic equipment, has undergone a few changes and updates.

Now designated RoHS 2, the new revisions include 3 new product categories:

  1. Medical devices.
  2. In vitro diagnostics medical devices.
  3. Control and monitoring instruments.

Also, products will be required to meet the new RoHS 2 directive in order to receive the CE marking.  No changes have been made to the restricted chemical list to date.

The RoHS 2 directive went into effect on January 2nd, 2013, however there are different effective dates for each new product category:

1. Medical Devices and Non-Industrial Control and Monitoring Instruments
Effective date:  July 22nd, 2014

2. In Vitro Diagnostic Medical Devices
Effective date:  July 22nd, 2016

3. Industrial Control and Monitoring Devices
Effective date:  July 22nd, 2017

To download the RoHS 2011/65/EU Directive, Click here: RoHS 2011/65/EU (PDF)
For a list of Frequently Asked Questions about RoHS 2, Click here: RoHS 2 FAQ (PDF)

APX is pleased to inform you that all of our products conform to the RoHS 2011/65/EU Directive (RoHS 2).