Purchased pair of power supplies from Connex. This is their their mid-power, heatsink-less power supply. When I ordered, Cristi of Connexelectronic was kind enough to inform me that a new version was in the works and asked me if I wanted to wait for the new model instead of getting the current model at that time. Obviously, I waited for the new model
The latest edition of this supply, the “RE” model, incorporates a CLC output filter to further clean up the output waveform. Factory measurements show 7-11 mV peak-to-peak @ +/-45V at 2A [link]. In addition, I like the following features:
- ‘Perfect” companion to the Hypex UCD-180 amplifier module in terms of size and power for a dual-mono configuration
- The input high-voltage capacitors have been increased in size (as compared with the photo of the older model)
- Based on the latest ST L6599A resonant controller
- $uper deal!
Here is a closer look at the output CLC filter. I we use the reported ripple value of 7-11 mV peak-to-peak for an output voltage of +/-45V, we get .011V/90V=0.012% or .009% RMS for the high value and .005 % RMS for the low value. These values are in the same ballpark as the (0.003%) number for a LM7805 regulator.
The input capacitors have been increased in size as compared with the photo in the Connex website (or this is the size for the 120V model. The 400V input caps are probably for the 200V world)
The auxiliary supply filter caps.
Here is the previous model without the CLC output configuration
The ST L6599A [link] is the resonant controller. This “resonant LLC” topology is widely used for the 80-Plus Gold and Platinum PS’s for PCs because it allows for highest efficiency( [example 1], [example 2]). There are also indications that Hypex is also using this topology for their SMPS: [link]
The use of resonant LLC also results in lower EMI emissions due to the soft switcingh of the FETs and sinusoidal current [link]. In hard-switching topologies, fast changes in voltage and current generally results in higher amounts of EMI.
TECHNOLOGY: CONVENTIONAL VS RESONANT
According to a Fairchild design document:
“The Conventional PWM technique processes power by controlling the duty cycle and interrupting the power flow. All the switching devices are hard-switched with abrupt changes of currents and voltages, which results in severe switching losses and noises.”
“Meanwhile, the resonant technique process power in a sinusoidal form and the switching devices are softly commutated. Therefore, the switching losses and noises can be dramatically reduced.”
“Among many resonant converters, the half-bridge LLC-type resonant converter has been the most popular topology for many applications since this topology has many advantages over other topologies; it can regulate the output over wide line and load variations with a relatively small variation of switching frequency, it can achieve zero voltage switching (ZVS) over the entire operating range, and all essential parasitic elements, including junction capacitances of all semi-conductor devices and the leakage inductance of the transformer, are utilized to achieve soft-switching.”
Soft switching is the main reason for much reduced EMI
The transformer has a new look -a cap- (don’t know if it is functional or just esthetics)
The output FETs are ST W20NM50. Specified at 500V / .22ohm /20amp. It is also rated at 14 amp continuous at 100 degrees C. Ample current carrying headroom mitigates the need for heat-sinks. These two parts alone are worth near 25% of the entire cost of the supply
Selecting mains voltage: 230V or 120V.
At first I was getting 0V. at the outputs. It turned out that the supplies are shipped for 230V operation. For 120V operation, the “120V jumper” must be installed (right photo).
Output voltage adjustment.
The nominal voltage of the supply is +/- 45V. There is a pot for voltage adjustment as shown in the photo below. I also replaced the output metal tabs for screw connectors for easier hookup.
These are the high and low values for the output voltage (previously measured with 330 ohm 10W power resistors loading the outputs)
I gutted an old discarded MUZAK PA amplifier and salvaged the case.
Reused the power cord and the lighted power switch. I added a ferrite bead to the power cord to further filter any potential EMI coming in our out through the power cable. The power supplies already have built-in EMI filters (as most SMTPs do).
The two green LEDs are connected to the auxiliary supplies and indicate that the power supplies are ON. I will later expose the LEDs from the UCD amplifier modules. Thus there will be light indicators for the AC in, the power supplies and the amplifier modules.
For testing and voltage adjustment, I use 1.5 Kohm 5W power resistors connected at the outputs.
The output voltage is very stable. The starting voltage is shown (44.96v). Eventually, it stabilizes at 45.00V.
In addition, with or without loading the outputs with the resistors, the power supplies are dead quiet (at least with my ears a few inches away from the supplies avoiding being zapped with high voltage :-)).