Switching power supply composed of LM324

What is Switch Mode Power Supply?
Switch Mode Power Supply (SMPS), also known as Switched Power Supply, Switching Converter, is a high-frequency power conversion device, is a power supply. Its function is to convert a level voltage into the voltage or current required by the user end through different forms of architecture. The input of a switching power supply is mostly AC power (such as mains power) or DC power, and the output is mostly equipment that requires DC power, such as a personal computer, and the switching power supply converts the voltage and current between the two. This paper introduces the scheme of switching power supply composed of LM324.

Switch Mode Power Supply

Commonly used series regulated power supply, because the regulating tube works in the amplification state, power consumption is large and efficiency is low. Especially in high-power power supply, the design is more complex. Generally speaking, the adjustment tube is seriously heated, and a large radiator or other heat dissipation device needs to be installed. Moreover, the amplification factor of the high-power transistor is low, and when the power supply is required to provide tens of amperes of current, the required driving current will be several amperes. Therefore, in the production of high-power DC power supply, it is appropriate to use switching voltage supply. Because the adjusting tube of the switching power supply works in the switching state, the efficiency is high, the power consumption is small, and the huge heat dissipation device can be omitted, and the volume of the power supply can be reduced. In recent years, power VMOS transistor is often used as a power switch tube, it is a voltage control element, almost no drive current, circuit design is more convenient. This paper introduces a switching power supply using a four-amplifier LM324, whose output voltage is continuously adjustable between 0- 40V, and the output current can reach 30A. The effect is satisfactory, and the principle block diagram is shown in Figure 1.

Schematic block diagram of switching power supply

The circuit consists of reference voltage circuit, comparison amplifier circuit (pulse width modulator), triangle wave generating circuit, photoelectric coupling circuit, sampling circuit and so on. After the reference voltage is determined, the comparator amplifier A3 compares and amplifies the sampled voltage Vf with the reference voltage Vz to obtain a DC voltage signal V1 which changes regularly according to the output voltage V0 and is applied to the non-inverting input terminal of the pulse width modulator A4. The triangular wave voltage V2 output by the triangular wave generator is applied to the inverting input terminal of the pulse width modulator A4, so that the output pulse width of the pulse width modulator A4 is controlled by the DC voltage of the non-inverting input terminal. After the triangle wave rises, when V1 is greater than V2, A4 outputs high level, and the switch tube is turned on through optical coupling.

Working waveform diagram of switching power supply

Actual circuit diagram of switching power supply

The actual circuit is shown in Figure 3. Comparator A1, resistors R1~ R7, capacitor C1 and bidirectional voltage regulator constitute a square wave generator. Its oscillation frequency mainly depends on C1, R2, R5, R6, f=1/2R2C1Cn (1 + 2/R6/R5), and VD1 is used to stabilize the output amplitude. Operational amplifiers A2, R8, R9, R10 constitute an integrator, which can convert the square wave output by A1 into a triangular wave with good linearity. Opamps A3, VD3, RP, R12, R13, R14, R15 constitute a comparator amplifier. A4 is pulse width modulator. When the output current increases to a certain value, the voltage drop on the resistor R19 makes the transistor VT2 conductive, so that the VT3 is conductive, the pulse signal added to the optical coupling is grounded, the switch tube is turned off, and the switch tube is protected.

Switching power supply composed of LM324