This paper introduces the internal structure, circuit characteristics, working principle and application circuit of the L4970A high-power monolithic integrated switching power supply chip. The L4970A series of high-power monolithic integrated switching power supplies is the second generation of ST's products following the L4960 series. The circuit is characterized by: DMOS switching power tube, hybrid CMOS / bipolar transistor and other integrated circuit manufacturing new technology; output voltage continuously adjustable in the range of 5. 1V ~ 40V; can be obtained by bootstrap capacitor Current output; the power-down reset circuit can send a signal to the microcomputer in real time to monitor the working state of the system power supply. 1 Working principle The block diagram of the L4970A is shown in Figure 1. (Note: The pin numbers apply to the L4970A/ 4975A/ 4977A). Its internal functional circuits mainly include reference voltage source, sawtooth generator, built-in 40kHz oscillator, undervoltage detection and overheat protection circuit, error amplifier, comparator, PWM latch, NOR gate, flip-flop (by two levels or Gate configuration), driver stage, DMOS switching power tube, current limit comparator, soft start circuit, power down reset circuit. The internal reference voltage source can output two reference voltages, one is V REF = 5. 1V for setting the output voltage V0 value; the other is V START = 12V, which cooperates with the bootstrap circuit to drive the driver stage The power supply voltage is increased by 12V. The open-loop voltage gain of the error amplifier is A VO > 60dB , the supply voltage rejection ratio is PMRR = 80dB, and the input offset voltage is 2mV. Figure 1 L4970A block diagram 1. 1 L4970A Series Turn-on Threshold Voltage The turn-on threshold voltage is V ON = 11V and has a hysteresis voltage of 1V. In order to ensure reliable operation of the chip, the minimum input voltage V L >11V is required, generally taking VImin15V. In order to provide a sufficiently large driving voltage for the DMOS switching power transistor, a bootstrap boosting method is employed. The bootstrap capacitor Cb is charged to 12V with an internal 12V reference and superimposed on the driver stage supply to boost it to (VI + 12V). 5A。 The DMOS power tube with a switching time of 50 ns, can work normally at a high frequency of 200 kHz, the peak drive current is about 0. 5A. 1. 2 PWM control loop The working principle of the PWM control loop is: firstly compare the feedback input voltage with the 5.1V reference voltage to generate the error voltage Vr; then compare Vr with the sawtooth voltage VJ to obtain a fixed frequency pulse modulated signal, driven by the driver stage. The DMOS power transistor is driven, and finally a buck output circuit composed of L, VD, and C is used to obtain a stable output voltage. In Figure 1, the synchronous input signal is applied to the sawtooth generator to provide a feedforward signal that provides good regulation over a wide input voltage range. The following focuses on the working principle of the current limiting circuit and the reset and power-down circuits. The principle of the soft-start circuit is identical to that of the L4960. 2000 puffs disposable vape pen are so convenient, portable, and small volume, you just need to take them 2000 puffs disposable vape,2000 puff vape pen,2000 puff e-cigarette kit,disposable vape 2000 puffs,2000 puffs vape kit Ningbo Autrends International Trade Co.,Ltd. , https://www.vapee-cigarettes.com
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