In many applications today, the required nominal input voltage exceeds the maximum VIN rating of many existing DC/DC controllers. Traditional solutions to this include using expensive front-end protection or implementing low-side gate drive devices. This means using an isolated topology such as a flyback converter. Isolated topologies typically require custom magnetics, and design complexity and cost are increased compared to non-isolated methods.
There is another solution that can solve the problem by using a simple buck controller with VIN max (maximum input voltage) that is less than the system input voltage. How is this achieved?
The buck controller is typically derived from a bias supply of reference potential (0V) (Figure 1a). The bias supply comes from the input voltage; therefore, the device needs to withstand the full VIN potential. However, since the gate drive voltage required to turn on the P-channel MOSFET is lower than VIN at VGS, the P-channel buck controller has a gate drive power supply with reference to VIN (Figure 1b). Turning off the P-channel MOSFET simply turns the gate voltage to VIN (0V VGS) (Figure 2).
Figure 1: VCC bias generation for N-channel (a); and P-channel controller (b)
Figure 2: Gate Drive for P-Channel Controller
The asynchronous P-channel controller derives its bias supply to drive the P-channel gate, which provides significant benefits and may provide a virtual ground that is suspended above 0V. For an N-channel high-side MOSFET, the voltage comes from a grounded reference supply. This is the charge pumped using the boost capacitor and diode to provide a gate voltage that is higher than the VIN source potential. This problem can be significantly simplified by using a P-channel high-side MOSFET. To turn on the P-channel MOSFET, the gate potential needs to be lower than the source potential of VIN. Therefore, the power supply only refers to VIN, not the VIN and ground mentioned above.
Suspension grounding
How do I create a floating ground for my controller? This is simple and can be achieved by using an emitter follower. Figure 3 shows the basic practice of this approach. The potential of the PNP emitter is Vbe (~0.7V), which is lower than the zener diode voltage potential (Vz). Essentially, you can float the controller to VIN and adjust the controller's reference to limit the voltage between VIN and device ground.
Figure 3: Creating a virtual ground using a simple emitter tracker scheme
Output voltage conversion
There is a challenge here that needs to be overcome. Since the controller is at virtual ground (Vz-Vbe) and produces a buck output voltage with a reference ground (0V) potential, how can the output voltage signal be converted to a feedback voltage above the virtual ground (typically between 0.8V and 1.25) Between V)? Figure 4 illustrates the specific challenges.
Figure 4: Schematic diagram showing the voltage potential difference between VOUT (reference 0V ground) and the controller's feedback voltage (refer to virtual ground)
To turn off the loop, you can use a pair of paired transistors to practice the circuit shown in Figure 5. A match pair sends the feedback signal to VIN; another match pair produces a current from VIN to the potential above the virtual ground.
Figure 5: Advanced schematic of a non-synchronous controller and feed practice using paired transistors
In summary
The LM5085 is ideal for my application because it is a P-channel non-synchronous controller with a VCC bias supply reference to VIN. In traditional applications, the LM5085 can withstand input voltages up to 75VIN. For applications where the input transient voltage is much higher than 75V, consider the solution presented here, which is 12V.
Starting from the controller feedback voltage of 1.25V, use the current to set the feedback (Ifb) to 1mA, and use Equation 1 to calculate the Rfb value:
Where Rfb = 1.25k.
Rfb1 sets the reference current of the current mirror. Again with 1 mA as the reference current and Equation 2, calculate Rfb1 to set the output voltage:
Where VOUT = 12V, Rfb1 = 11.3k, and Vbe is ~0.7V.
The reference current Iref2 is set when 1 mA flows into Rfb2 and the emitter current is approximately equal to the collector current (Ie to Ic). The loop is closed and the voltage will be adjusted to the stated set voltage.
Output voltage regulation
This idea is suitable when the transient voltage is significantly higher than the absolute maximum of the LM5085. The LM5085 is a constant on-time (COT) controller; therefore, its on-time (Ton) is inversely proportional to VIN. However, when VIN is clamped to the LM5085, Ton will no longer adjust as VIN (to power level) increases because the device will have a fixed voltage set by the Zener diode and VIN (to power level) will continue Increase. This will cause the frequency to drop because the increase in the power stage input voltage exceeds the clamping voltage of the LM5085; therefore the regulated voltage may start to increase slightly. Therefore, the magnitude of the ripple injection voltage is specified to ensure the Type 1 ripple injection standard. Ultimately, ensure that ripple is specified to an acceptable level to maintain stability and minimize output errors as ripple increases.
Example schematic
Figure 6 shows a schematic of a 48V supply with an absolute maximum VIN rating of 150V. An example can provide 12VOUT under 3A conditions.
Figure 6: Using the LM5085 in a 3A design with 24V to 150VIN (max) / 12VOUT
Figure 7 shows the efficiency diagram obtained from the prototype board. The two parameters are efficiency (%) and load current (A).
Figure 7: Relationship between efficiency (%) and load current (A) at different input voltages
Figure 8 shows the switching node voltage and inductor ripple current at 150 VIN.
Figure 8: Channel 1 Switch Node Voltage, Channel 4 Inductor Ripple Current
in conclusion
You can use a P-channel non-synchronous buck controller in applications where the system input voltage is higher than the device's maximum input voltage rating. The advantage of this application is the use of lower cost controllers and minimizing component count.
Bitcoin mining is the process of creating new bitcoin by solving puzzles. It consists of computing systems equipped with specialized chips competing to solve mathematical puzzles. The first bitcoin miner (as these systems are called) to solve the puzzle is rewarded with bitcoin. The mining process also confirms transactions on the cryptocurrency's network and makes them trustworthy.
For a short time after Bitcoin was launched, it was mined on desktop computers with regular central processing units (CPUs). But the process was extremely slow. Now the cryptocurrency is generated using large mining pools spread across many geographies. Bitcoin miners aggregate mining systems that consume massive amounts of electricity to mine the cryptocurrency.In regions where electricity is generated using fossil fuels, bitcoin mining is considered detrimental to the environment. As a result, many bitcoin miners have moved operations to places with renewable sources of energy to reduce Bitcoin's impact on climate change.
Btc Miner,Bitmain S19 Xp,Bitmain Antminer S19 Xp,Antminer Bitmain S19 Xp 140Th
Shenzhen YLHM Technology Co., Ltd. , https://www.sggminer.com