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The Application of CFM500M and CFM500S Series in Series Connection



#Technical Article#AC-DC Power Supply#Medical#Industrial / ITE#Baseplate-cooling / Fanless

Jun 18, 2021

The Application of CFM500M and CFM500S Series in Series Connection



With the rapid development of power converter technology, the use of high-efficiency power supplies has been a great step forward. There has been growing demand for the compact size but high-power density power supplies. To achieve optimal efficiency and the end-product design, power supplies in series, in turn, are employed to increase the output voltage and the overall output power. This article aims to demonstrate Cincon’s CFM500M240 as an example to achieve power modules in series use to increase the output voltage and power application.


Product Introduction:

Cincon’s CFM500M/S Series are the compact size but high-power density AC-DC switching power modules. They come with input voltage range from 80 to 264Vac and offer output voltages of 12Vdc, 18Vdc, 24Vdc, 36Vdc, and 48 Vdc. The units, with efficiency up to 94.5%, are based on the power module architecture of PFC+LLC. Also, CFM500M/S Series support a 5V standby power and 12V fan power supply and offer the signal of PS On/Off remote control, fan control, power good, and power fail as the control applications that are beneficial to customer’s system. The modules are equipped with fully protected functions, including Continuous Short Circuit Protection, Over Current Protection (OCP), Over Voltage Protection (OVP), and Over Temperature Protection (OTP). The unit sizes are both 3 x 5 inches with baseplate or enclosed cooling solution. They can work under the ambient temperature range from -40°C to 85°C, which is for customers more flexible to install in various types of system. CFM500M Series has IEC/EN/UL 60601-1 approvals suitable for medical applications and CFM500S Series has IEC/EN/UL 62368-1 standard suitable for industrial and ITE applications.


CFM500M240 Connected in Series:

Engineers exploit two sets of CFM500M240 power supplies with 24V output voltage to conduct the experiment to test each power supply connected in series with a view to increasing output voltage and output power. The two power supplies (SP1 and SP2) are connected in series as shown in Figure 1.


The output of each power converter requires a diode connected in parallel that serves as an alternative path of the current to avoid triggering the protection. If either of the power supplies starts the protection mode, the output current flows into another one, which could damage the internal components. The voltage rating of the diode therefore shall exceed Vout to prevent reversed voltage; simultaneously peak forward surge current shall be greater than rated output current.


CFM500M240 Connected in Series

Figure 1. CFM500M240 Connected in Series


The two sets of CFM500M240s share the same input AC source and are connected in series with single output of 24V respectively, which can obtain an overall stable 48V output voltage. The load currents are respectively 50% and 100% of total rated output current in series connection. The steady waveforms of the output voltage and current connected in series are shown in Figure 2.


Figure 2-1 Figure 2-2
CH2: Iout, 50% of rated load
CH4: Vout
CH2: Iout, 100% of rated load
CH4: Vout

Figure 2. The Steady Waveforms of the Output Voltage and Current Connected in Series


The graphs below illustrate the dynamic response of the power supplies connected in series. Figure 3 reveals that the dynamic waveforms of the output current vary from 50% to 100% and 100% to 50%. Figure 4 illustrates that the instantaneous waveforms of the output current vary from 0% to 100% and 100% to 0%. The findings demonstrate that when the load current is changing, the system of output voltage and current remains stable.


Figure 3-1 Figure 3-2
CH2: Iout, 50%→100% rated load
CH4: Vout
CH2: Iout, 100%→50% rated load
CH4: Vout

Figure 3. The Dynamic Waveforms of the Output Current Vary from 50% to 100%.


Figure 4-1 Figure 4-2
CH2: Iout, 0%→100% rated load
CH4: Vout
CH2: Iout, 100%→0% rated load
CH4: Vout

Figure 4. The Instantaneous Waveforms of Output Current Vary from 0% to 100%.


The graphs below show the waveforms of output voltage and output current during starting up and the load currents are respectively 50% and 100% of the rated output current. As Figure 5 reveals, the SP1 is first activated, and subsequently the SP2 starts up. Even though the power modules start up at different moments, the overall output voltage and current in series will reach a state of stability after the completion of starting up.


Figure 5-1 Figure 5-2
CH2: Iout, 50% of rated load
CH4: Vout
CH2: Iout, 100% of rated load
CH4: Vout

Figure 5. CFM500M240 Starting Waveforms of the Output Voltage and Current in Series


As for the efficiency curve, the input voltages, when CFM500M240 connected in series, are 115Vac and 230 Vac, and the results are illustrated in Figure 6. While the maximum output power is 1000W, the efficiency could reach up to 94.5%. The evidence presented thus far supports the findings that the efficiency of the two power modules is not influenced by being connected in series.


The Efficiency Curve of CFM500M240 in Series

Figure 6. The Efficiency Curve of CFM500M240 in Series


Output Remote Sensing:

If the load is farther away from the power modules, this might increase the power consumption. However, Cincon’s CFM500M/S Series are capable of offering remote sensing function for adjusting the output voltage to compensate for the voltage drop caused by the distance. CFM500M/S Series, when connected in series, can automatically adjust the output voltage to fulfill the requirement of the regulated voltage at the point of load. This is the ideal method of distributing and stabilizing the output voltage to the device. The diagram is shown below.




The purpose of this article demonstrates how to carry out the application of power modules connected in series by two sets of Cincon’s CFM500M240s as an example to increase overall output power and voltage. This case study confirms that the two sets of CFM500M240 power supplies connected in series can maintain a stable 48Vdc output voltage and the output current. Another significant aspect is that the load of two power modules in series varies, while the output voltage and current of the system can remain stable. On the other hand, when the power module operates with the maximum output power, its efficiency can reach up to 94.5%. These findings reported above indicate that CFM500M/S Series, based on the proper operation, are suitable for being connected in series with high performance and efficiency to elevate the overall output power and raise the output voltage. These series, in effect, are perfect for use in medical equipment (CFM500M Series), and information and other industrial applications (CFM500S Series).


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