With the rise of virtual currencies, computer host devices optimized for virtual currency algorithms, known as “mining machines,” have surged in popularity. Since the second half of 2017, the skyrocketing price of Bitcoin has also driven up the demand for mining machines. The booming mining machine business has also led to a surge in demand for mining machine power supplies, especially for 1kW to 3kW high-efficiency power supplies.
The interleaved PFC + phase-shifted full-bridge architecture has been widely used in high-power power supply applications and is very mature and reliable. TI provides a complete solution. The PFC solution uses UCC28070, a two-phase interleaved CCM PFC controller that achieves high power factor (PF) values and efficiency. Many high-power analog PFC solutions in the industry use this device. The high-voltage DCDC after the PFC stage uses UCC28950, which is a phase-shifted full-bridge control chip with synchronous rectification, particularly suitable for high voltage, high efficiency, and low EMI applications. The primary side driver uses UCC27714, a 600V 4A high-side/low-side gate driver; the synchronous rectification driver uses UCC21520, a 5.7 kVrms dual-channel isolated gate driver.
TI High-Power Power Supply Solutions
The UCC28070 PFC controller operates in CCM mode and employs a unique 180° interleaving technique to maximize PFC efficiency, reduce losses, and distribute heat generation more evenly, simplifying thermal design. Compared to single-ended PFC, it greatly reduces the current ripple of the bus electrolytic capacitors, thereby reducing the size of the bus capacitors.
PFC Output Capacitor Ripple Current (Comparison of Interleaved PFC and Single-Ended PFC)
The optional programmable frequency jitter mode of the UCC28070 allows designers to spread the turn-on and turn-off frequencies within a certain range, minimizing electromagnetic interference (EMI) generation. This jitter feature helps reduce capacitor size, enabling designers to use smaller and cheaper EMI filters.
PR779 is a 1.2kW universal input (85 to 270 VRMS) interleaved PFC converter reference design with a 390 VDC output. Under 115 Vac and 20% to 100% load conditions, it achieves an efficiency of over 95%. For the same load group, if the input voltage is 230 Vac, the efficiency can reach over 97%. For the same load range, whether at 115 VAC or 230 VAC input, the power factor is greater than 0.98. This design complies with the current EN61000-3-2 requirements. The design consists of two circuit boards: the main board PR779 (containing power system components) and the sub-board PR780. The sub-board contains all the control circuits required to drive the power system. This control is based on the UCC28070 continuous current mode interleaved PFC controller.
As the mining difficulty of Bitcoin increases, the industry has raised higher requirements for the reliability and efficiency of mining machine power supplies. Long-term stable operation directly affects mining profits, and conversion efficiency relates to mining costs. Compared to traditional PFC full-bridge rectification, the bridge-less PFC saves losses caused by diode rectifier bridges, further improving power conversion efficiency. The SLUA517 application manual provides a bridge-less PFC solution using the UCC28070. For a 2KW mining machine power supply, the bridge-less solution can reduce rectifier bridge losses by 20W. Based on an electricity cost of 0.3 yuan per kilowatt-hour, for a mining cycle of 2 years per machine, this can save 105 yuan in electricity costs.
UCC28070 Bridge-Less PFC Solution
The UCC28070 offers various unique system control and protection features to enhance overall system reliability. The output over-voltage protection scheme, combined with open-loop detection features, can prevent common circuit board failures. Each phase current is accurately balanced, and with the independent current sensing function, it can prevent components from overheating in dual-phase operation mode. Additionally, the UCC28070 provides under-voltage lockout, cycle-by-cycle peak current limiting, and system over-temperature protection features.
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