Notes on choosing a switching power supply?

1) To increase the reliability of the switching power supply, we suggest users choose a unit that has a rating of 30% more power than actual need. For example, if the system needs a 100W source, we suggest that users choose a S.P.S. with 130W of output power or more. By doing this, you can effectively boost the reliability of the S.P.S. in your system.

2) We also need to consider about ambient temperature of the S.P.S. and whether there is additional device for dissipating the heat. If the S.P.S. is working in a high temperature environment, we need to make some derating to the output power. The derating curve of "ambient temperature" versus "output power" can be found on our spec sheets.

3) Choosing functions based on your application:

* Protection function: Over Voltage Protection (OVP), Over Temperature Protection (OVP), Over Load Protection (OLP), and etc.

* Application function: Signaling Function (Power Good, Power Fail), Remote Control, Remote Sensing, and etc.

* Special function: Power Factor Correction (PFC), Uninterruptible Power Supply (UPS) function.

What is minimum load requirements from the spec?

There are some minimum-load requirements on multi-output power supplies. Please read the specification first before connecting to the load. In order to allow the power supply to work properly, a minimum load for each output is required, or else, the output voltage level will be unstable or outer tolerance range. Please refer to Current rangein the specification as shown in the table below: Channel 1 requires a 2A minimum-load; channel 2 requires 0.5A; Channel 3 requires 0.1A ; Channel 4 does not need any minimum-load.

Output Number CH1 CH2 CH3 CH4
DC Voltage 5V 12V -5V -12V
Rated Current 11A 4.5A 1A 0.5A
Current Range 2~12A 0.5-4.5A 0.1~1A 0~1A
Why did the power supply shuts down during operation and after turning it off, I can restart the power supply again?

In general there are two circumstances that will cause the power supply to shut down. The first one is the activation of the over-load-protection (OLP). To deal with this situation, we suggest increasing the rating of the output power or modifying the OLP point. The second one is the activation of over-temperature protection (OTP) when the internal temperature reaches the pre-set value. All of these conditions will let the S.P.S. enter protection mode and shut down. After these conditions are removed, the S.P.S. will be back to normal.

What is PFC?

Power Factor Correction(PFC) is to improve the ratio of apparent power to real power. The power factor is around 0.4~0.6 in non-PFC models. In models with PFC circuit, the power factor can reach above 0.95. The calculation formulas are as follows: Apparent Power=Input Voltage x Input Current (VA), Real Power= Input Voltage x Input Current x Power Factor (W).
From the point of view of environment friendly, the power plant needs to generate a power which is higher than apparent power in order to steadily provide electricity. The real usage of electricity is defined by real power. Assuming the power factor is 0.5, the power plant needs to produce more than 2WVA to satisfy 1W real power usage. On the contrary, if the power factor is 0.95, the power plant only needs to generate more than 1.06VA to provide 1W real power, It will be more effective in energy saving with PFC function.
Active PFC topologies can be divided into single-stage active PFC and two-stage active PFC, the difference is show as in the table below.

PFC topology Advantage Disadvantage Limitation



active PFC

Low cost

Simple schematic

High efficiency in


watt application

Huge Ripple

complex feedback


1.Zero hold up time. The output is affected by the AC input directly.

2.Huge ripple current results in lower LED life cycle.(drive the LED directly)

3.Low dynamic responds, easily affected by load.


Two-stage active PFC

High efficiency

Higher PF

Easy feedback control

High adoptive against

load condition


Higher cost

Complex schematic

Suitable for all kinds use

What is the difference between -V and COM which are marked on the output side?

- COM (COMMON) means common ground. Please see below:

Single output: Positive pole (+V), Negative pole (-V)

Multiple output (Common ground): Positive pole (+V1, +V2) , Negative pole (COM)

The output ground (GND) and frame ground (FG) is the same point in my system, can BST power supplies be used in such system?

Yes. Since our products are designed based on isolation concept, it will be no problem that the output ground (GND) and frame ground (FG) is the same point in your system. But, EMI may be affect by this connection.

During the operation of your power supply, there is some leakage current on the case. Is this normal? Will this leakage current hurt human body?

Due to the requirement of EMI, there will be some Y capacitors between line and neutral to the FG (case) to improve EMC. These Y capacitors will cause some leakage current flow from line or neutral to the case (normally case will be connected to earth ground). For example, IEC-60950-1 requires that this current should be less than 3.5mA for IT equipment, so basically the leakage current you find on the case will not hurt human body. Proper connection to Earth ground will solve the leakage current problem.

For certain need, is it possible to reduce the noise of fan?

Noise is directly related to the fan which is build into the power supply. Lowering the airflow of the fan means reducing the heat dissipation ability. It will also influence the reliability of the products. Furthermore, minimum airflow of fans is defined by Safety Organization and a safety appendage will be needed if using a new fan. Generally, when we choose a suitable power supply, fan is not necessary if wattage is under 150W. Between 150~500W, both fan and fanless products are available. Above 500W, a fan is needed.

What is the warranty of BST products?

BST offer 2 yeas warranty

If the product have quality problem during warranty period, we will provide maintenance service;  We will not be responsible for shipping and installation cost which incurred by improper installation, misuse or tampering with the units.

If any problem during using, you can contact us freely, we will do our best to help with you.


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