lab power supply
|Output voltage range
|Limited current range
|Minimum voltage step
|Minimum current step
|Output voltage slope
|Maximum voltage applied to shutdown
|Output voltage measurement resolution
current measurement resolution
*1. The upper limit
of the output
voltage and current are subject to change. It be transformer determined.
and schematic features
In order to obtain a
minimum level of noises in PSA2 was used the linear regulator.
In classical designs of laboratory PSU the output stage is usually
supplied from fixed voltage from the rectifier, sometimes using
multiple levels of discrete switching using relays, thyristors, FETs,
or linear output stage with multilevel supply.
Thus the control element output stage radiate considerable power,
especially at low output voltage and high current when the voltage drop
on it as much as possible.
Multi-level supply output stage improves the situation, but requires an
increase in the number of circuit elements and the power filter
- In order
to reduce radiated power the output stage in PSA2 is
powered from automatically regulated voltage.
For this reason the rectifier combined with
pre-regulator where applicable phase (angular, vertical)
Output voltage of the pre-regulator supported so as to provide the
minimum necessary voltage drop across the linear regulator.
The phase angle for opening the key are microcontroller calculated.
Used solution scales
well and allows you to create a laboratory PSU
with different maximum values of output voltage and current. However,
the feasibility of building a lab PSU with a linear regulator for large
(over 2..3A) current is significant doubt: usually load requiring low
noise consumes little current, and for heavy loads better to have a
separate switching PSU. Based on this assumption PSA2 design oriented
to maximum current of 2..3A (maybe 4..5A, but not desirable) and
the voltage to 30..50V essentially unchanged.
The transformer is the most expensive part of the design. Moreover, not
everyone has the opportunity, materials and skills relevant to rewind
the transformer. Because of this, the requirements to the transformer
Perhaps the use of relevant transformers from various old devices.
Necessary that the
transformer has only two independent windings: low
power winding for supply of control circuit (recommended voltage 12 ..
15V at a current load to 0.4 A suitable series connection of two
heating windings 6.3 V), and powerful, whose parameters have chosen to
provide maximum output voltage and current. For example, for a PSU with
a maximum output voltage of 30V required winding, which is will get
about 40V after the rectifier at the maximum current load (respectively
about 30V AC voltage at the maximum current load).
Possible to use two separate transformers for the power section and the
The control circuit is required 12V stabilized voltage, which must be
galvanically isolated from power winding. Other voltages of control
circuit receiving from this 12V.
The measurement circuits of output voltage and current are separated
from the feedback circuits of linear regulator.
Common is just only shunt of current measurement.
- In order to increase
the resolution of the ADC the oversampling was used.
- Resolution is 1mV and
- Control circuit based
on the STM32 microcontroller in 64-pin package with a 0.5mm pitch.
- Desirable to use
commutatorless 12V-fan for cooling. Fan speed is regulated through MCU
based on the settings, current mode and heatsink temperature.
- As the temperature
sensor can be used DS18B20 or DS18B20+PAR (planned but not implemented
yet now DS18S20, TMP35, KTY81).
- Used 16x2 character
LCD. You can use the indicator without any national charset (currently
the menu only English language)
Currently such operating modes supported: stabilization of current and
voltage in classical
CV/CC mode, or disabling
the output in transition
mode of current or voltage stabilization with adjustable delay.
function is similar to trigger mode and have the difference that until
shutdown current is limited.
Output of the PSA2 is protected for any polarity and
amplitude of applied voltage which does not exceed the maximum output
voltage (even if the mains power is switched off). Off-state leakage
current is determined by the resistance of the feedback circuit of the
linear regulator and of the input impedance of voltage measurement
channel (at all more than 40 kOhms).
The most PSU available for amateurs have no output disable buttons.
In this case usually shutdown occurs via the power switch.
The PSA2 have
special button for disable output.
- Adjustable rate of
output voltage slope during starting.
- Simulated voltage
ripple frequency of 50-60 Hz or 100/120 with adjustable amplitude
- Fixed settings
(presets) that are specified by the user.
- Measurement of load
- Measurement of load
- Measurements of energy
(Wh), capacity (Ah). Automatic shut down upon reaching the preset value
- Preset profiles to
charge some popular types of batteries (planned).
Bluetooth module is not required, PSU fully retains all
its functions without Bluetooth module, so if it does not need the module can be absent.
The schematic will be assembling on two PCBs (look of two sets of PCBs from
- The control
circuit board PSA201C (from front,
front without indicator,
dimensions of 110 x 80 mm.
It contains control circuit, stabilizers 5V and 3.3V, measuring
amplifiers, shunt current measurement, error amplifier, elements of
isolation interface 232, an optional module Bluetooth, output
protection circuit, controls (buttons, encoder), LCD, LED, boozer.
Output terminals also connected to control PCB.
The PCB mounted to the front panel using the 4 pcs nylon standoff
The rectifiers and
output stage board PSA201P (
bottom side) has dimensions of 100 x 36 mm and be fasten to
the heatsink on the rear of the PSA2 via installed power components
Due to its small size and weight an additional mechanical fastening is
usually not necessary.
This board also provide 12V supply for control circuit and fan.
Connections between boards (see layout
is performed an 16-wire cable with IDC connectors and 2-wire cable with
a cross section of at least 0.75 mm2
The transformer, extra filter capacitor, optional surge protector are
fasten on the chassis.
The power switch fasten directly on the front panel. Connections
between the power switch and transformer is desirable to use of the
detachable connector type MF-2M and MF-2F or similar.
Due to high demands on the assembly the PSA2 not recommended for beginners.
Strictly not recommended apply changes to the PCB layout
because it can cause to poor precision and perhaps even the
In case of differences between the
list of parts and schematic
circuit please remember the list of parts is more true.
In case of differences on reference designators between
PCB silkscreen and assembly
drawing please remember the assembly drawing is more true.
- Recommended first mount
all SMD components. Then all through-hole components except switches,
encoder, display and terminal blocks. Then wash PCB.
Then mount the remaining parts.
All power transistors
must be isolated from the heatsink.
In case mount of transistors on insulating pads
always check insulation resistance of each element before
first turning on.
In case of using 2-wire connection to mains recommend that the heatsink
In case of using a 3-wire connection cable the PE wire can be connect
directly to the heatsink and to the metal chassis of the transformer
Capacitor C1 can be mount directly on the terminals of the transformer
T1 (if terminals strong), or other available means, and carefully
This capacitor must be
Class X2 or Class X1 (specially designed for
operation in mains circuits). In case of use regular film capacitor
please choose voltage at least 630V, but it is strictly not
- In case of use a
toroidal transformer which must be fasten on metal or on the
flame-proof glass-reinforced epoxy laminate base, which is then
fastened to the housing.
It is not advisable to exclude fuses F1 and F2. F1 fuse holder can be
mounted on the rear cover, or on the additional mains filter PCB, or
directly on the wire inside the device.
As a F2 fuse holder a car holder fuse BladeType or miniBlade can be
used, which is installed directly on the wire.
- All connections of
primary power circuits must be carefully insulated.
Auxiliary filter capacitor C2 can be gather from several smaller
These capacitors can be installed inside device and fastened in any
way, for example via metal clamp.
Perhaps the use of a small PCBs or part of breadboards.
Connection to PSA201P board must be made via two wires with cross
section of at least 0.75 mm2
Capacitance of the C2 capacitors is chosen at the rate of about 5,000
uF at 1A of the maximum output current.
Maximum operating voltage of those capacitors must be at least 1,6×UIIx.x.
For example, when a idle AC voltage of secondary winding is 30V the
capacitor C2 must be at least 50V
- Connecting to a PC can
be done via the RS232 port or via an USB-UART adapter.
- The recommended
front panel assembly.
- The design is oriented
to use Z2AW
shell type from Kradex, other
shells may require a changes
of front panel.
replacements of components
Control circuit is based on STM32-family MCU.
Now firmware was checked on STM32F100R8T, STM32F100RBT, STM32F103RCT,
F101 and F102 sub-family not to be supported.
Also will not supported STM32F100R4T, STM32F100R6T, STM32F103R6T,
- Error amplifier based
on opamp type AD823AR.
Possible to use other opamp in the same housing of SO-8 with the same
arrangement of terminals. Must work from 12V supply, and allow near the
0V inputs, with inputs currents are not more few nA, slew rate is more
than 1V/µsec, offset voltage less than 10mV and offset voltage drift
not more than 5µV/°С
Measuring amplifier based on opamp type AD8572AR.
Possible to use other opamps in the same housing of SO-8 with the same
arrangement of terminals.
Must work from 3V supply preferably with a small (no more than 1..2mA)
current consumption, allowing operation near 0V on inputs, with
Rail-toRail output, with a few nA of the inputs current.
The slew rate does not matter.
Offset voltage must be less than 10mV and offset voltage drift must not
Despite the relatively high offset voltage (few mV) due to the low
(about 4µV/°C) offset voltage drift here AD8542AR works well.
- Rightly assembled from
undamaged parts PSU does not require any adjustment.
Need to do only initial calibration of voltage (voltmeter is required)
and current (ammeter is required).
The accuracy of output voltage and current depends from quality of the
Calibration can be repeated any number of times if necessary.
The calibration voltage is independent of the calibration current and
an contrary, and can be performed separately. But at the first time
need the full calibration procedure.
- If when you first start
LCD have insufficient contrast (or nothing visible) can be repeated
powered on with button F1 pressed, afterward try to set the desired
The rotation of the encoder must be accompanied by a beep.
If audio signals present, but rotation encoder does not lead to an
acceptable contrast, you can measure the voltage between pin.2 and
pin.3 of LCD. It should be 4..5V
If any questions
please feel free to contact:
the full project or any parts, the original circuit decisions,
software, construction and/or design solutions, without the written
consent of the author are prohibited.
Please read necessarily the warnings
and the license agreements.