Isolated 3.3V to 5V converters are commonly used in long-distance data transmission networks where the bus node controller operates from a 3.3V supply to conserve power while the bus voltage is 5V to ensure long-distance transmission. Signal integrity and high drive capability. Although there are already isolated DC/DC converter components with 3.3V to 5V conversion on the market, the integrated 3.3V to 5V converter is still difficult to find. Even if found, these particular converters (especially those with stable outputs) typically have longer product delivery times, are relatively expensive, and generally have some isolation voltage limitations. If the application requires isolation voltages above 2kV, converter efficiency above 60%, or reliable reliability of standard components, discrete design is a low-cost alternative to integrated components. The disadvantage of discrete DC/DC converter design is that it requires a lot of work - choose a stable oscillator structure and a break-before-make circuit, select a MOSFET that can be effectively driven by a standard logic gate, suitable for temperature and long-term reliability testing. All these efforts take time and money. Therefore, before the warehouse promotes such a plan, the designer should consider the following: The integrated components usually pass the temperature test and have other industrial qualifications. These components are not only the most reliable solution, but also have a faster time to market. Unstable output converters typically cost $4.50 to $5.00 per 1,000 units, while stable output converters are typically twice the price, about $10.00 or higher. Therefore, it is reasonable to buy a converter with an unstable output, or use a step-down capacitor to buffer the output or send it to a low-cost, low-dropout regulator (LDO) such as TI's TPS76650. The discrete DC/DC converter design shown in Figure 1 uses only some of the existing standard components (such as logic ICs and MOSFETs) to serve the transformer driver and an LDO for stabilizing the output voltage. The circuit uses a number of through-hole components to make the prototype, making it larger than the integrated components, but thanks to TI's Little LogicTM devices, board space is greatly reduced. The main benefits of this design are fewer bill of materials (BOM) and the freedom to choose an isolation transformer for isolation voltages in the 1 to 6kV range. Our goal is to provide a low-cost alternative by making the transformer driver stage a stable output fully integrated DC/DC converter and stand-alone transformer driver. Figure 1 Isolated 3.3V to 5V push-pull converter working principle Low cost, isolated DC/DC converters are typically push-pull drive types. The working principle is very simple. A square wave oscillator with a push-pull output stage drives a center-tapped transformer whose output is rectified for stable or unsteady DC use. An important functional requirement is that the square wave must have a 50% duty cycle to ensure symmetric magnetization of the transformer core. Another requirement is the product of the magnetization voltage (E) and the magnetization time (T) (called the ET product in units of Vμs) and must not exceed the typical ET product of the transformer specified by its manufacturer. We must also install the break-before-make circuit next to the oscillator to prevent the two transformer cores in the push-pull output stage from conducting at the same time, causing circuit failure. Discrete design The famous three-inverting gate oscillator consists of U1a, U2a and U2b, which is chosen because it is more stable in terms of power supply fluctuations. With a 100-pF ceramic capacitor (COSC) and two 10-kΩ resistors (ROSC1 and ROSC2), its normal frequency is set to 330kHz. The oscillator has a duty cycle of approximately 50% and a maximum frequency fluctuation of less than ±1.5% over a 3.0-V to 3.6-V supply voltage fluctuation range. Figure 2 shows the waveforms at the addition point of ROSC1 and ROSC2 (TP1) and the oscillator output (TP2). All voltages are measured with reference circuit reference voltage. Figure 2 Oscillator waveforms for TP1 and TP2 The Schmitt trigger circuit NAND gates (U1c, U1d) implement the break-before-make function to avoid overlapping of the MOSFET turn-on phases. The other two NAND gates (U2c, U2d) are configured as inverting buffers to produce the correct signal polarity necessary to drive the N-channel MOSFETs (Q1, Q2). Figure 3 shows the complete break-before-make action. To accommodate the limited drive capability of standard logic gates, we chose MOSFETs because of their lower total charge and shorter response time. Figure 3 waveform after breaking first The isolation transformer (T1) has a 2:1 secondary to primary turns ratio, a 0.9 mH primary coil inductance, and a guaranteed isolation voltage of 3kV. Figure 4 shows the input and output waveforms of the transformer. Fish Collagen,Fish Collagen Powder,Fish Collagen Granules,Cod Skin Collagen Ningbo Nutrition Food Technology Co.,ltd. , https://www.collagenworkshop.com