Review, teardown, and testing of RSP-150-24 Mean Well power supply

General description

A short description

The RSP-150-24 is a universal input power supply with a constant output voltage of 24 volts and a current of up to 6.3 amperes. According to the specification, it has an operating AC input voltage range of 85 to 370 volts without manual switching. The supply measures close to 7.8 × 3.9 × 1.2 inches (199 × 99 × 30 millimeters) and is made on a printed circuit board fixed to the base of the metal case, designed to operate with passive cooling. The top lid covering the case is perforated.

The power supply has an LED indication for the output voltage and allows one to adjust it within -5 to +10%. This unit does not have either PFC or thermal protection.

Design description

The input and output circuits of the power supply are connected to a common screw block (1). From left to right, there are three terminals for the input line, neutral, and ground wires, and two parallel blocks of two terminals for the outputs: ground and +24V.

The input voltage from the screw terminals is supplied to the RF interference filter (2) and through the fuse (3) to the diode bridge (5). Next, the rectified voltage is supplied to the active PFC, controlled by the PFC+PWM controller FAN4800 (4). The power part of the PFC is assembled using a MOSFET 19NM50N (6) and an 8A 600V ultrafast diode STTH8S06D (7). The output voltage from the PFC is supplied to the two-transistor forward converter, whose transistors, 14NM50N (9), are controlled by the same controller, FAN4800. The converter voltage from the transformer (10) is supplied to the rectifier and to the LC filter (13, 14). The output rectifier is made using MBR20150 diodes (12). The filter output capacitance is 470 uF, 35 V, designed for operating temperatures up to 220F (105C) (14).

General stabilization control is performed by the AP4310 chip. The control signal is transmitted from it to the high-voltage part of the circuit through a transistor optocoupler (15). One optocoupler serves as the main regulation channel, the second forms a backup channel for overvoltage protection (OVP), and the third provides reception of a remote control signal.

To limit the inrush current, there is an NTC (18) connected to the output stage of the rectifier bridge (5) near the boost inductor PFC.

The rectifier bridge (5), transistors, and diodes (6, 7, 9, and 12) are pushed against the housing with screws using overhead metal strips. Between the aluminum case and the board (from the solder side), there is an extra insulation layer, a thin sheet of fiberglass. All bulky components are additionally fixed using compound.

Build quality is good.

Test conditions

Most tests are performed using Metering Setup #1 (see appendices) at 80F (27C), 70% humidity, and 29.8 inHg pressure.

The measurements were performed without preheating the power supply with a short-term load, unless mentioned otherwise.

The following values were used to determine the load level:

Output voltage under a constant load

The high stability of the output voltage should be noted.

Power-on parameters

Powering on at 100% load

Before testing, the power supply is turned off for at least 5 minutes with a 100% load connected.

The oscillogram of switching to a 100% load is shown below (channel 1 is the output voltage, and channel 2 is the current consumption from the grid):

The picture shows three distinguishable phases of the power-on process:

1. The pulse of the input current charging the input capacitors when connected to the grid has an amplitude of about 4.5 A and a duration of about 5 ms.

2. Waiting for the power supply control circuit to start for about 50 ms.

3. (Output Voltage Rise Time) Output voltage rise takes 6 ms.

(Turn On Delay Time) The entire process of entering the operating mode from the moment of powering on is 61 ms.

(Output Voltage Overshoot) The switching process is aperiodic; there is no overshoot.

Powering on at 0% load

The power supply is turned off for at least 5 minutes before the test, with a 100% load connected. Then the load is disconnected and the power supply is switched on.

The oscillogram of switching to a 0% load is shown below:

The picture shows three distinguishable phases of the power-on process:

1. Charging the input capacitors when connected to the grid has an amplitude of about 1.5 A.

2. Waiting for the power supply control circuit to start for about 27 ms.

3. (Output Voltage Rise Time) Starting the converter, increasing the output voltage, and entering the operating mode take 4 ms.

(Turn On Delay Time) The entire process of entering the operating mode from the moment of powering on is 31 ms.

(Output Voltage Overshoot) The switching process is aperiodic; there is no overshoot.

Power-off parameters

The power supply was turned off at 100% load, and the input voltage at the moment of powering off was nominal. The oscillogram of the shutdown process is shown below:

The oscillogram shows two phases of the shutdown process:

1. (Shutdown Hold-Up Time) The power supply continues to operate due to the input capacitors holding charge until the voltage across them drops to a certain critical level, at which maintaining the output voltage at the nominal level becomes impossible. The phase takes 20 ms.

2. (Output Voltage Fall Time) Reduction of the output voltage, stopping voltage conversion, and accelerating the voltage drop take 6 ms.

(Output Voltage Undershoot) The shutdown process is aperiodic; there is no undershoot.

The current waveform at 100% load right before shutdown is close to sinusoidal with an amplitude of 2 A.

Output voltage ripple

100% load

At 100% load, the low-frequency ripple is approximately 15 mV.

At 100% load, the ripple at the converter frequency is approximately 50 mVp-p, and the noise is 70 mVp-p.

75% load

At 75% load, the low-frequency ripple is approximately 10 mV.

At 75% load, the ripple at the converter frequency is approximately 20 mVp-p, and the noise is 30 mVp-p.

50% load

At a 50% load, the low-frequency ripple is approximately 6 mV.

At 50% load, the ripple at the converter frequency is approximately 30 mVp-p, and the noise is 50 mVp-p.

10% load

At a 10% load, the low-frequency ripple is approximately 10 mV.

At a 10% load, the ripple at the converter frequency is approximately 30 mVp-p, and the noise is 50 mVp-p.

0% load

No-load current consumption measured with a multimeter: 29 mA.

(Power Consumption) The first assumption of excessive standby power draw of more than 6.5 watts is wrong, since the current in this mode is predominantly reactive. Indeed, the input filter in the circuit contains two capacitors with a combined capacitance of 1.5 μF.

Measuring the exact active power consumption at a 0% load with a basic set of instruments (oscilloscope, multimeter, etc.) is not possible.

At 0% load, the low-frequency ripple is approximately 2 mV.

At 0% load, ripples at the converter frequency are masked by the 80 mVp-p noise.

Dynamic characteristics

To evaluate the dynamic characteristics, a mode with periodic switching between 50% and 100% load was used. The oscillogram of the process is shown below:

It is clear that the power supply, when the load changes abruptly, allows for a slight dampening overshoot; the magnitude of the response to load changes is about 260 mV.

Overload protection

The claimed protection type is "constant current limiting, recovers automatically after the fault condition is removed." This was confirmed during testing. When the output is overloaded or shorted, the unit goes into current stabilization mode and automatically restores operation when the overload goes away.

The output current for the overload protection to kick in is 7.9 A.

Input circuit safety assessment

(Input discharge) Safety assessment is based on the discharge time constant of the input circuits when disconnected from the grid; the value is 0.126 s. This means that when operating on a 120 V input voltage, the time required to discharge the input circuits to safe values (<42 V) will be 0.2 s:

Important: The result is valid for this particular power supply unit; it was obtained for testing purposes and should not be taken as a safety guarantee.

The leakage current at the ground pin is 24 µA.

Thermal conditions

When operating with no load connected, no component overheating had been noticed.

Thermograms were captured at three power levels: 80, 90, and 100%, fully assembled and with the lid removed. Thermal images show that the most loaded element of the block is the input thermistor (NTC), and its heating seriously stands out against the background of all the other components. At 80% load, it heats up to 220F (104CC, 140F above ambient temperature). At 90%, it's 221F (105C, 141F above ambient), and at 100%, it reaches 236F (108C, 156F above ambient).

80% load

90% load

100% load

Conclusions

RSP-150-24 generally has little noise and ripple, the output voltage is maintained accurately, and the build quality is solid.

The dynamic characteristics of this unit aren't great; when the load pulses, the power supply can't adjust itself in time. This results in quite noticeable spikes and overshoots.

For long-term operation, the load should be limited to 70–80% of the nominal one., especially during the hot season when ambient temperatures reach 95F (35C) or more.

Important: The results are valid for this particular power supply unit; they were obtained for testing purposes and should not be used to evaluate all the units of the same type.