In a world loaded with tons of Switched Mode Power Supplies (SMPS) it became clearer than never that no matter the bulky size and weight, the Linear Power Supplies have more advantages than faults.
That’s why a small-size LPSU L-50 suitable for replacing the noisy SMPSes used for powering network streamers, DACs, audio players, Raspberry Pi-based boards, USB-powered digital equipment etc. has been designed and offered for sale for several years.
Following its warm acceptance and taking into account all considerations and new ideas, accumulated during the years after L-50’s initial release, a new version of this LPSU was designed and is proudly presented here.
The new version retains the form-factor of its predecessor (the size/shape of the case, heatsink and IN/OUT connectors), but all other components became subject of a deep redesign:
– During the process of R&D, the LPSU has been considered as a DC amplifier which allows to directly implement some of the well-known LF amplifier’s solutions for gaining the best possible PSRR. As a result the impressive 20 dB gain in PSRR was achieved (compared to the predecessor L-50).
– The size and the placement of the PCB were changed, which allows a better routing of the PCB traces and more optimal components’ placement.
– Extensive usage of more sophisticated components for achieving the best performance possible.
– Input voltage: AC 115V or AC230V (according to the destination country or user request)
– Output voltage: DC 5V/12V/15V (user-defined values are also available upon request)
– Max. output current – 2.5A
– User selectable option for 6mm. aluminum front panel (black or white anodized)
– Dimensions: 115x170x60 mm.
– Transformer Power: 50VA
– Weight: about 2.2kg
– Front panel LED
– Output DC cable with barrel jack 5.5/2.5 mm., 5.5/2.1 (OD/ID) or micro-USB connector
– Possibility for different output connectors upon customer’s request
– Possibility for upgrade of DC cable with custom-made one
– The regulator has all-discrete topology. No Operational Amplifiers are used. This allows complete design control over all operating points and parameters for superior performance. Low noise, high PSRR.
– The bridge rectifier, used in the earlier LPSU version is replaced by TL4320 ideal diode bridge controller driving high-efficient, low capacitance MOSFETs. This helped not to only avoid the voltage drops in the diodes’ p-n junctions (and hence their overheating at high currents) but most important – to change the spectrum of the switching currents during the ON/OFF times without use of some expensive and inefficient HEXFRED, SiC etc. diodes.
– The simple electrolytic capacitor, filtering the output of the bridge rectifier is replaced by two-stage CRC filter. Capacitor from the well renowned among audio society Nichicon MUSE series is used as a first electrolytic capacitor in the filter (which mostly determines the filter’s “sound signature”), followed by high-quality PWR200 series Vishay Thick film resistor. The second (main reservoir) electrolytic capacitor is from high quality EPCOS/BC Components brand.
– Low-noise, high-quality Vishay Mini-MELF resistors are used in the whole regulator’s “signal” path.
– Dual (matched) transistors chips are used in the regulator’s key places (differential error amplifier, current mirror etc.) which ensures the excellent thermal stability and equality of their parameters and further contributes for the improved performance.
– A Zener diode is used as a voltage reference. It is fed by a Constant Current Source attached to the output of the regulator which dramatically minimizes the noise and ripple through the Zener (and hence at the input of error amplifier). The High-frequency Zener noise is additionally filtered by a Low-pass filter between Zener diode and error amplifier.
– A special over-voltage, over-current and over-heating protection circuitry constantly monitors the output voltage, current and the temperature of the heatsink.
If the output voltage pass above a small predefined level, the over-voltage protection is activated and the output is immediately “semi”-shorted by a low-value power resistor. This prevents the further, dangerous rise of the output voltage and in turn triggers the circuitry for over-current protection.
The over-current protection constantly monitors the output current and trips when it goes above a predefined value. This protection circuitry can work in a trigger mode (the regulator’s output stage is constantly held in non-conducting mode and in order to restore the normal work regulator must be turned off for a couple of minutes) or as a current-limiter (the output current is held at constant value). When the over-current condition is gone, the regulator returns in its normal state without need of restart.
When the regulator is in the current-limiting state and/or a proper air ventilation of the heatsink is not ensured in the absence of an over-heating protection, the temperature of the output transistor can raise to a degree when it will suffer by a thermal runaway and will be destroyed with possible catastrophic outcome for the regulator or attached appliance. Of course the SAFETY is a thing we care about a lot, so the over-heating protection constantly monitors the heatsink’s temperature and turns OFF the output transistor when the temperature goes above a given threshold, preventing it from thermal destruction.
An optional EMI/RFI filter can be attached to the transformer’s AC Mains input. The filter use a choke with high-quality nano-crystalline core and RIFA/KEMET X2 polypropylene capacitors.
Measurements of DC and AC voltages were taken with Keithley 2015 Multimeter while the spectrum plots were drawn using RTX 6001 Audio Analyzer. The obtained results are as follows:
– Line regulation (AC input voltage between 216 – 235 V): better than 0.05%
– Load regulation (DC output current between 0 – 2 A): better than 0.05%
– Measured Power Supply Rejection Ratio (PSRR): -145 dBu for fundamental harmonic (100 Hz)
A DC cable ended with barrel jack 5.5/2.5 or 5.5/2.1 mm (OD/ID) is provided along with the unit. In case some different connector is required contact us prior to place the order.
Instead of the standard DC cable a custom made one can be used: https://www.atlhifi.com/shop/audio-cables/dc-cable-upgrade-for-l-100-lpsu/
This is a “star-quad” cable which consists of 4-wire AWG22 silver plated wires with PTFE insulation.
The unit is available with thick aluminum front panel (milled and anodized) or without panel while retaining all functionality.
User can also choose between 3 fixed output voltages – 5, 12, 15V or Custom defined voltage.
In case you want a LPSU with Custom output voltage (different from the 3 listed above), please contact us via the contact form in order to discuss the possibility for LPSU production. Then in the process of ordering you should leave a note for desired output voltage.
What the buyer will receive:
The package will contain 1 pcs. FULLY ASSEMBLED and tested Linear Power Supply L-50 v.2 in a steel case and 1 pcs. DC cable.
Note: The AC Power cable is not provided.
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