Introduction to Circuit of Each Functional Module
1.The function of the rectifier circuit in APC UPS power supply is to convert the low voltage AC power output by the AC voltage reduction circuit into unidirectional pulsating DC power. This is the rectification process of AC power. The rectifier circuit is mainly composed of rectifier diodes. After passing through the rectifier circuit, the voltage is no longer AC voltage, but a mixed voltage containing DC voltage and AC voltage. It is commonly referred to as unidirectional pulsating DC voltage. The figure shows the input curve and output curve, which convert AC power into unidirectional pulsating DC power. By utilizing the single-phase conduction characteristic of diodes, the output curve is entirely on the positive half axis, resulting in pulsating DC current output.
The rectifier transformer has three roles in design:
(1) It can expand the adjustment range of the thyristor control angle in the rectifier circuit and improve the adjustment performance.
(2) Perform isolation function. It isolates the rectifier circuit from the power supply of the grid, preventing direct electrical contact between them. This can reduce the interference and impact of the grid on the rectifier/charging circuit, and also reduce the interference of the rectifier/charging circuit on other electrical equipment on the grid.
(3) Hypotensive effect. The rectifier transformer converts the grid voltage into a voltage that matches the load, which helps improve the performance of the thyristor rectifier. In general, the secondary voltage of the rectifier is lower than the primary voltage of the primary side, so the rectifier transformer here is a step-down transformer. Its wiring method should be coordinated with the synchronous transformer wiring to meet the phase relationship between the main circuit and the synchronous voltage.
2. Other circuits
(1)APC UPS power filtering circuit: The filtering method generally uses passive components such as capacitors or inductors to achieve the purpose of filtering by utilizing their energy storage characteristics for voltage and current. Due to the energy storage function of reactive components in the circuit, the parallel capacitor C can store some energy when the voltage supplied by the power supply increases, and release the energy when the power supply voltage decreases, making the load voltage relatively smooth, that is, the capacitor C has a smoothing effect; The inductor L connected in series with the load stores energy when the current supplied by the power supply increases (caused by an increase in power supply voltage), and releases energy when the current decreases, making the load current relatively smooth, that is, the inductor L also has a smoothing effect. There are many forms of filtering circuits, and in order to understand their analysis rules, they are divided into capacitive input type (capacitor C is connected at the front) and inductive input type (inductor is connected at the front). The former type of filtering circuit is mostly used in low-power power supplies, while the latter type of filtering circuit is mostly used in high-power power supplies (and when the current is high, an inductor is connected in series with the load)
(2) Power on/off control: The power on/off control circuit is executed by a relay. When the relay is closed, the signal output by the limiting amplifier is short circuited to ground, and the subsequent circuit stops working to achieve the purpose of shutdown.
(3) Pre driver: The pre driver circuit is a voltage follower that does not amplify, but only drives the power amplifier circuit to provide sufficient driving current for the power transistor.