Isolation describes the electrical separation between the input and output of a dc-dc converter. An isolated dc-dc converter uses a transformer to eliminate the dc path between its input and output. In contrast, a non-isolated dc-dc converter has a dc path between its input and output. Non-isolated dc-dc converter designs usually employ ICs specifically intended for that purpose.
Figure 1 shows the basic schematic for an isolated converter, and figure 2 the non-isolated.
The benefits of using non-isolated DC-DC converters
In general, non-isolated converters are less flexible in use than their isolated cousins. However, they do bring a number of benefits for designers where isolation is not required.
The primary difference is that a non-isolated converter does not have a transformer and does not require any physical separation between input and output, so this typically makes them smaller and lighter. It also improves the efficiency as there are no transformer losses to take into consideration. The design of non-isolated converters tends to be simpler as no isolation is required in any signals crossing the isolation boundary, removing the need for optoisolators and / or signal transformers. This reduction in BOM means that non-isolated converters tend to be lower in cost.
Following are some applicable models for non-isolated DC-DC
LM27761
Texas Instruments CSD25310Q2 20V P-Channel NexFET Power MOSFET
Features
Product Summary
1• Ultra-Low Qg and Qgd
• Low On Resistance
• Low Thermal Resistance
• Pb-Free Terminal Plating
• RoHS Compliant
Texas Instruments CSD25310Q2 20V P-Channel NexFET Power MOSFET is a 19.9mΩ, –20V P-Channel MOSFET that is designed to deliver the lowest on-resistance and gate charge. This is done in the smallest outline possible with excellent thermal characteristics in an ultra-low profile. The CSD25310Q2's low on-resistance coupled with an extremely small footprint in a SON 2mm×2mm plastic package makes the device ideal for battery-operated space-constrained operations.
CSD13302W 12 V N Channel NexFET™ Power MOSFET
Features
Product Summary
1• Ultra Low On Resistance
• Low Qg and Qgd
• Small Footprint 1 mm × 1 mm
• Low Profile 0.62 mm Height
• Pb Free
• RoHS Compliant
• Halogen Free
CSD13302W- This 14.6 mΩ, 12 V, N-Channel device is designed to deliver the lowest on resistance and gate charge in a
small 1 x 1 mm outline with excellent thermal characteristics and an ultra low profile.
LM27761 Low-Noise, Regulated, Switched-Capacitor Voltage Inverter
Features
1• Inverts and Regulates the Input Supply Voltage
• Low Output Ripple
• Shutdown Lowers Quiescent Current to 7 µA (Typical)
• Up to 250-mA Output Current
• 2.5-Ω Inverter Output Impedance, VIN = 5 V
• ±4% Regulation at Peak Load
• 370-µA Quiescent Current
• 2-MHz (Typical) Low-Noise Fixed-Frequency Operation
• 35-dB (Typical) LDO PSRR at 2 MHz With 80-mA Load Current
• 30-mV LDO Dropout Voltage at 100 mA, VOUT = –5 V
• Current Limit and Thermal Protection
• Create a Custom Design Using the LM27761 With the WEBENCH® Power Designer
The LM27761 low-noise regulated switched-capacitor voltage inverter delivers a very low-noise adjustable output for an input voltage in the range of 2.7 V to 5.5V. Four low-cost capacitors are used in the application solution to provide up to 250 mA of output current. The regulated output for the device is adjustable between −1.5 V and −5 V. The LM27761 operates at 2-MHz (typical) switching frequency to reduce output resistance and voltage ripple. With an operating current of only 370 µA (charge-pump power efficiency greater than 80% with most loads) and 7-µA typical shutdown current, the LM27761 provides ideal performance when driving power amplifiers, DAC bias rails, and other high-current, low-noise voltage applications.
Summary
Isolation is a very useful feature within power solutions as it is able to provide safe operation, reduce noise / ground loops and allow flexibility in how the voltage rails are configured with respect to one another.
However, where non-isolated converters are able to be used, designers are able to take advantage of smaller size, higher power density, better efficiency and lower costs.
The intermediate bus architecture has been popular for several decades and, until recently, the IBC has been an isolated device. However, as this approach is finding new applications such as high-performance computing and datacoms, isolation is not required in the IBC as it is already present in the front-end SMPS. In this scenario, designers are able to take advantage of using non-isolated IBCs such as the BMR350, BMR351 and BMR310 from Flex Power Modules.
Previous： Electric power steering (EPS)
