The basic schematic design of the switching power supply is as simple as this

Basic schematic diagram of switching power supply

1. Primary circuit: Directly connected to the external grid power supply.

2, secondary circuit (Secondary Circuit):

The part of the circuit that is isolated from the primary side of the device.

3. Y-capacitor: A high-voltage capacitor that is connected between a circuit and ground or a secondary circuit.

Switching power supply grounding, leakage current, withstand voltage test (safety)

1. Ground Continuity Test:

A. Definition: From the Inlet PG end through the current to the user can touch the ground, to ensure that its resistance is less than the specification value, to achieve the function of grounding protection.

B. Standard: B.1 Input current is not more than 25A, (DC or AC) voltage does not exceed 12V, time is at least 3 seconds (TUV requirement). B.2 Test result: Resistance value should not exceed 100 mΩ.

2. Earth Leakage Current Test:

A. Definition:

Through a "body impedance analog circuit" approved by the safety unit (UL, TUV, CSA...), measuring the flow of the object to be tested (SPS) between the accessible metal parts and the ground when the device (SPS) is powered on Electricity flow.

B. Standard Huai:

B.1 The input voltage is 106% of the upper rated voltage. B.2 Test result: Class I≦3.5mA; Class II≦0.25mA.

3. Dielectric Withstand Voltage Test:

A. Definition: Also known as high-voltage dielectric test, Hi-pot (High Potential) Test, high voltage is applied from the primary side to the secondary side (or primary side to ground) to determine the isolation voltage of the internal insulation layer. The function.

B. Standard: B.1 The input voltage is as follows:

B.2 Test results: There is no insulation breakdown (Breakdown).

The difference between the withstand voltage test AC and DC

Calculation method of leakage current in withstand voltage test

1. DC test leakage current setting: DC test current is very small (μA), generally DC high voltage is applied between the primary side and the secondary side, and the leakage current is set: 0μA~100μA.

2. Theoretical calculation of leakage current in AC test:

Calculation formula: I = 2Ï€ * f * V * Cy

Where f - test voltage frequency (50Hz or 60Hz) V - test voltage (unit: volt)Cy - the sum of the Y capacitances between the primary side and the ground or between the primary and secondary sides.

Therefore: Imin = 2Ï€ * f * V * CyminImax = 2Ï€ * f * V * CymaxCy Capacitance calculation: Cy = Cy1 + Cy2+Cy3 +...

If a Y capacitor (Cy0) is connected between the primary side ground and the secondary side ground, then

Y capacitor tolerance is generally: +/-20% OR +/-10%

3. The following factors should be considered when actually setting the AC test leakage current:

(1). Consider the initial leakage current: the initial leakage current is the measured leakage current in the state without the object to be tested.

(2). Consider Y capacitance tolerance: When the power supply engineer selects the Y capacitor of the same capacity, there are often several models, but the tolerances are different (some are +/-10%; some are +/-20%), give The actual leakage current setting is troublesome, so we should set it by +/-20% tolerance. Otherwise it must be set according to +/-10% tolerance.

(3). Consider the distributed capacitance existing in the actual line, so the leakage current range is set: (lower limit is rounded: upper limit is rounded)

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