DC/DC Modules

The power-budget is often known at the very end of a design project. Therefor the use of a DC/DC module increases the chances to Time-To-Market for the product. The right DC/DC module manufacturer does not only offer a solution to the conversion demand, but is also helping with requirements on filter, transient protection and other environmental demands.

Today, efficiency of most DC/DC modules is between 75 and 97.5%. Modules that has galvanic isolation are less efficient due to losses in the isolation. Efficiency is often given at a constant full load condition at 25 °C ambient temperature. By choosing DC/DC module from real, varying load conditions over time, both board space and money can be saved. A DC/DC with higher efficiency at lower load may be the right choice for the application instead of the module that shows the highest efficacy figure at the top of the datasheet.

A common requirement in different standard is galvanic isolation. An isolated module can be used to increase noise immunity or for offering another ground potential. Within telecommunication 48 V DC and positive ground is used on the input side, when negative ground is used on the outputs. Medical applications have high requirements on isolation and leakage currents, typically specified in IEC60601. Isolated DC/DC modules have lower efficiency than non-isolated modules, since isolation materials increase the losses.

The graph of efficiency overload at different input voltages is a helpful tool when calculating how much dissipated heat that must be handled. If the dissipated heat is handled in a good way it will increase the lifetime of the application. A common way of cooling DC/DC modules when there is low natural air flow, is cooling through a base plate. The base plate can be mounted on to the chassis or to a heat sink.

The railway industry lacks a standard for the DC-bus, corresponding to the 28 V within avionics or 48 V within telecommunications. Each country defines their own input bus voltage, anything from 24 V DC to 110 V DC. EN50155 defines different voltage limits, the lowest 0.6 times nominal Voltage to the highest 1.4 times nominal voltage. An input voltage range from 14.4 V to 154 V is needed to ensure that a railway equipment can be used in different countries.

The most common input voltages in avionics is 28 V DC, 270 V DC and 115 V AC. An input voltage range of 16 to 40 V DC or 70 to 180 V AC is needed to cover standards used worldwide. Transients and voltage drop down to 0 V must also be managed. Gaïa Converter has filter modules, pre-regulator modules, hold-up modules, DC/DC modules and AC/DC modules to meet applicable standards such as MIL-STD-461 and DO-160.

For military vehicles the requirements are specified in MIL-STD-1275, that was released in its first version MIL-STD-1275A the 17th of September 1976 and in it’s latest version MIL-STD-1275E the 22nd of March 2013. The older version is still applicable when older vehicles are updated with new equipment. The latest standard MIL-STD-1275E address vehicles with several batteries. A though requirement in MIL-STD-1275E is the capability to handle transients with high energy content of up to 2J. Gaïa Converter offers solutions up to 300 W, either DC/DC modules that with a minimum of external components meets the spec, or with DC/DC modules in combination with filter modules and pre-regulators to meet the highest demands.
 
Thanks to new semiconductors in combination with new topologies, the new MGDD family from Gaïa Converter offers wide input voltage range in combination with different output voltages. The MGDDI-series has 12 to 160 V input voltage and therefor address many different batteries. The challenge has been to offer high efficiency over the complete input voltage range to keep the operating temperature within reasonable limits for the lifetime of the module. The new MGDD modules has two separate output voltages that can be used independently, in parallel, in series or symmetrically.  Two 24 V outputs can be used in series to achieve 48 V for a 60 W DC/DC module with 12 to 160 V input voltage. With a trim function outputs such as 7.2 V, 9.6 V or why not 19 V for laptops can be offered. The flexible output in combination with the input voltage range makes it possible to solve different conversion demands with one module.

Comptronic AB       Phone: 08-564 706 70       E-mail: mailbox@comptronic.se       Address: Stormbyvägen 2-4, 163 55 Spånga       Mon-Fri: 08.30–17.00