Seasonic Prime Fanless 700 W Review

Name: Seasonic Prime Fanless 700 W
Brand: Seasonic
Price: 266 USD

crmaris

on Jan 3rd, 2022,

in Power Supplies.

Manufacturer: Seasonic

Voltage Regulation Stability & Ripple »

Component Analysis

Before reading this page, we strongly suggest looking at this article, which will help you better understand the insides of a PSU.

Seasonic Prime Fanless TX-700 Parts Description
General Data
Manufacturer (OEM)	Seasonic
PCB Type	Double-Sided
Primary Side
Transient Filter	5x Y caps, 3x X caps, 2x CM chokes, 1x MOV, 1x Champion CM02X (Discharge IC)
Bridge Rectifier(s)	2x Vishay LVB2560 (600 V, 25 A @ 105 °C)
Inrush Current Protection	NTC Thermistor (MF72-5D20L) (5 ohm) & Relay
APFC MOSFETs	2x Infineon IPP60R099C7 (600 V, 14 A @ 100 °C, Rds (on): 0.099 ohm)
APFC Boost Diode	1x CREE C3D06060A (600 V, 6 A @ 154 °C)
Bulk Cap(s)	2x Nippon Chemi-Con (400 V, 470 uF each or 940 uF combined, 2,000 h @ 105 °C, KMR)
Main Switchers	4x Infineon IPP50R140CP (550 V, 15 A @ 100 °C, Rds (on): 0.14 ohm)
IC Driver(s)	2x Silicon Labs Si8230BD
APFC Controller	On Semiconductor NCP1654
Switching Controller	Champion CM6901T2X
Topology	Primary Side: APFC, full-bridge & LLC converter Secondary Side: synchronous rectification & DC-DC converters
Secondary Side
+12 V MOSFETs	8x Infineon BSC014N04LS (40 V, 125 A @ 100 °C, Rds (on): 1.4 mOhm)
+5 V & +3.3 V	DC-DC Converters: 6x Infineon BSC0906NS (30 V, 40 A @ 100 °C, Rds (on): 4.5 mOhm) PWM Controllers: ANPEC APW7159C
Filtering Capacitors	Electrolytic: 1x Nichicon (4–10,000 h @ 105 °C, HE), 1x Nichicon (2–5,000 h @ 105 °C, HD), 1x Nippon Chemi-Con (4–10,000 h @ 105 °C, KΒY), 1x Nippon Chemi-Con (5–6,000 h @ 105 °C, KZH), 1x Rubycon (3 - 6,000 h @ 105 °C, YXG), 1x Nippon Chemi-Con (4–10,000 h @ 105 °C, KY) Polymer: 14x FPCAP 10x Nippon Chemi-Con
5V to 5VSB ORing SBRs	3x MCC MBR1045ULPS SBR (45 V, 10 A)
Supervisor IC	Weltrend WT7527V (OCP, OVP, UVP, SCP, and PG)
5VSB Circuit
Rectifier(s)	1x Infineon IPA65R1K5CE FET (650 V, 3.3 A @ 100 °C, Rds (on): 1.5 ohm) 1x MCC MBR1045ULPS SBR (45 V, 10 A)
Standby PWM Controller	Leadtrend LD7750R

The PCB is large to increase the space between parts for better airflow. Moreover, there are heatsinks everywhere since there is no active cooling. Even the main transformer is fitted with a heatsink, which is good since it can get quite hot. To offer better load regulation on the minor rails and increase efficiency through lower energy losses on power transfers, the DC-DC converters handling these rails are on the modular PCB. A thick cable is used to feed the VRMs of the minor rails 12 V—a bus bar would have been better.

The transient/EMI filter stages include five Y and three X caps. Two CM chokes and a Champion CM02X discharge IC are also used.

A Metal Oxide Varistor (MOV) handles voltage surges, while an NTC thermistor and relay combination suppresses large inrush currents.

The bridge rectifiers are powerful, able to handle up to 50 A of current, which is way more than what this power supply will require.

The APFC converter uses two Infineon FETs and a CREE boost diode, which I expected to be stronger since all parts for this PSU are over spec. The bulk caps are by Chemi-Con, and their combined total capacity is 940 uF, so the hold-up time will easily exceed 17 ms.

The APFC controller is an On Semiconductor NCP1654. It is on a vertical daughter-board, which looks strange since it is quite small, so it would easily fit on the main PCB. Seasonic probably did this for ease of swappability.

The four main FETs are by Infineon and installed in a full-bridge configuration.

The unit's main transformer has a large heatsink on top of it to help it keep its temperatures low.

This photos shows the unit's resonant controller and resonant tank, parts of the LLC resonant converter.

The FETs regulating the +12 V rail are installed on the solder side of the main PCB. Heatsinks on the other side of the PCB handle their thermal load.

Two DC-DC converters generate the minor rails. They are installed on the modular PCB to be closer to the peripheral and main ATX sockets for lower voltage drops.

Seasonic used topnotch caps since there is no active cooling and their operating temperatures will be higher than typical. Many polymer caps are used, and these are significantly more tolerant to high operating temperatures than electrolytic ones.