Psu Manual

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Lab Power Supply Manual
Alex Striff
June 14, 2019
Contents
1 Acknowledgments 1
2 Motivation 1
3 Safety Notice (Grounding) 1
4 Usage Instructions 2
4.1 Setting the output voltage . . . . . . . . 2
4.2 Setting the current limit . . . . . . . . . 2
4.3 Indicator LEDs . . . . . . . . . . . . . . . 2
4.4 Monitoring the output current . . . . . . 2
4.5 Monitoring the internal temperature . . 2
4.6 Disabling the internal load . . . . . . . . 2
4.7 Calibrating the current limit . . . . . . . 3
4.8 Calibrating the output error indicator . 3
5 Principles of Operation 5
5.1 The LT3081 linear regulator . . . . . . . 5
5.2 The internal load . . . . . . . . . . . . . . 5
5.3 The Hot indicator circuit . . . . . . . . . 5
5.4 The Vout error indicator circuit . . . . . . 5
6 Schematic Diagram 7
7 Printed Circuit Board Layers 8
7.1 Front Copper . . . . . . . . . . . . . . . . 8
7.2 Back Copper . . . . . . . . . . . . . . . . . 9
7.3 Front Solder Mask . . . . . . . . . . . . . 10
7.4 Back Solder Mask . . . . . . . . . . . . . 11
7.5 Front Silk Screen . . . . . . . . . . . . . . 12
7.6 Front Fabrication . . . . . . . . . . . . . . 13
7.7 Plated Through-Hole Drill Map . . . . . 14
7.8 Non-Plated Through-Hole Drill Map . . 15
7.9 User Comments . . . . . . . . . . . . . . . 16
7.10 Edge Cuts (Board Outline) . . . . . . . . 17
List of Tables
1 Electrical Characteristics . . . . . . . . . 4
2 Bill of Materials . . . . . . . . . . . . . . 18
Colophon
The schematic diagram and printed circuit board lay-
out were both created with KiCAD. This manual was
compiled using L
A
T
E
X. Relatively fine (
0.51 mm
) lead-
based solder and mildly activated rosin flux were re-
quired to solder the components to the PCB.
1 Acknowledgments
The creation of this lab power supply was generously
funded by the Reed College Physics Department. I
would like to thank Edgar Perez for his kind advice, as
well as Lucas Illing for supporting this project.
2 Motivation
Often when working in electronics, several voltage
sources are needed. In addition to a main power rail,
one may need a complementary negative power rail for
analog circuitry, or a different logic power supply at
3.3 V
instead of
5 V
. Low-impedance bias voltages are
also a frequent requirement, needed for biasing BJTs,
comparator inputs, and more.
For most applications, a power supply fulfilling the
requirements of these applications need not be capable
of supplying much more than
1 A
of current, must have
a stable voltage output (requiring a linear regulator),
and must have a current limiting function. Addition-
ally, it would be nice if the power supply was much
smaller than a conventional
30 V
,
3 A
output bench
power supply with a large transformer, being conve-
niently powered from a common wall plug, batteries, or
any other DC power source at hand. I have attempted
to construct such a power supply.
3 Safety Notice (Grounding)
Please note that the negative voltage output of the
supply is directly connected to the negative voltage
input to the supply. That is, the output voltage of the
supply floating relative to earth ground if and only if
the input voltage is floating.
If you are uncertain if the supply (or any other piece
of equipment) is floating, it is quick and simple to check
if this is the case. Set a digital multimeter to its resis-
tance measurement or continuity check mode. Connect
one probe to the negative output of the PSU (the black
five-way binding post) or to the other terminal in ques-
tion, and then connect the other probe to earth ground.
This can be done either by insertion in to the earth
socket of a wall outlet, or by touching the outside of a
BNC connector on any nearby oscilloscopes, as these
are almost always earth grounded. If inserting into
a wall outlet, be certain that you know which hole is
which, and that you are using a multimeter approved
for wall testing (most are).
If the output is not floating (earth-referenced), then
one must be careful to only connect oscilloscope ground
leads to the negative output of the supply. Whatever
the ground lead is connected to will be shorted to earth
ground. If an incorrect connection is made, then con-
nected circuit components, oscilloscopes, or computers
(e.g. through USB) may be damaged. If you are uncer-
tain, connect probes as if the circuit is not floating.
If the output is floating (or if you know which termi-
nals are earthed and which are not), then the supply
may be safely connected to other voltage sources in
whatever configurations are convenient, such as in a
dual-rail setup.
4 Usage Instructions
4.1 Setting the output voltage
Connect a voltmeter to the output of the supply. You
may use either the binding posts or the test points
labeled on the board to achieve this. Turn the PSU
on and adjust the voltage using the coarse and fine
adjustment knobs as needed. Note that the maximum
output voltage is about 1.5 V below the input voltage.
4.2 Setting the current limit
To set the current limit to its minimum value, short the
minimum limit jumper (labeled Min Lim,
JP1
). To set
the current limit to higher than this value, the jumper
must be open.
The current limit is set to fixed values by moving
the switches on the board. The default values are 1,
2.5, 5, 10, 25, 50, and
100 mA
. To set the limit to any of
the upper four values, the switch for the lower values
must be in its rightmost position, as indicated on the
board.
Alternatively, the switch section on the board may
not be populated, and a
10 kΩ
(preferably 10-turn)
potentiometer (
RV4
) may be soldered in to provide a
continuously variable current limit.
To set the current limit to its maximum value, open
the no limit jumper (labeled No Limit,
JP2
). To set
the current limit to lower than this value, the jumper
must be shorted. The maximum value is about
2.0 A
in normal operation, and less when the device shuts
down to prevent overheating.
4.3 Indicator LEDs
The power supply includes two indicator LEDs for
when output voltage regulation is not guaranteed.
The Hot indicator LED (
D2
) lights when the main
regulation IC (see Section 5.1) starts to get hot (when
the junction temperature is about
100 ◦C
or above).
This light is a warning, and the output should continue
to be regulated as normal. If the IC continues to heat
up (to a junction temperature of
125 ◦C
), then internal
protection circuitry will prevent damage and reduce
the output voltage.
The
Vout
Error (
I
lim) indicator LED (
D1
) lights
when the actual output voltage is not sufficiently close
to the set output voltage. The most common cause for
this is if the current limiting function is active, but
internal protection circuitry or a set voltage that is too
high may also cause an output error.
4.4 Monitoring the output current
If it is not preferred to use an ammeter to measure
the output current, the
Iout
test point is provided for
convenient measurement or external control of the
load current. The signal at
Iout
is one volt for every
ampere of output current, including the internal load
(see Table 1 and Section 5.2). For example, if the supply
is outputting
25 mA
total, then
Iout
should read
25 mV
.
4.5 Monitoring the internal tempera-
ture
For more quantitative information about the tempera-
ture of the main regulation IC (see Section 5.1) than
is provided by the Hot indicator LED, the Temp test
point is provided. The signal at Temp is one millivolt
for every degree Celsius of junction temperature. For
example, if the junction temperature of the IC is about
73 ◦C
(subject to variation inside the IC), then Temp
should read 73 mV.
4.6 Disabling the internal load
The internal load may be disabled by opening the In-
ternal Load jumper. Note that this will increase the
2
current limit by at most
4 mA
above the current limit
displayed on the switches or that previously set by
RV4
, if installed. For most purposes, the Internal Load
jumper should be in its normal, shorted position (see
Section 5.2).
4.7 Calibrating the current limit
The power supply requires a minimum load in order to
regulate the output voltage properly. An internal load
usually supplies this minimum load (see Section 5.2),
but this offsets the effective current limit on the output.
A trimmer potentiometer is provided to compensate for
this offset.
Set the supply to the minimum limit as described
in Section 4.2. Using a screwdriver, adjust the poten-
tiometer (labeled Load Offset,
RV1
) until the output
voltage is stable (no current limiting), and then care-
fully reverse direction and adjust until the current
limit just starts to activate. This may be judged by
checking the output voltage with a voltmeter, or by us-
ing the built-in indicator if it is calibrated as described
in Section 4.8
4.8 Calibrating the output error indi-
cator
The issues associated with creating a reliable output
error indicator are discussed in Section 5.4. If neces-
sary, a trimmer potentiometer (
RV5
) may be populated
to correct the default setting by the resistor R21.
Attach a voltmeter to the PSU and set the output
voltage to
1 V
. Attach an external potentiometer to
the output of the supply, valued to draw a typical cur-
rent for your application. Set the PSU current limit so
that increasing the load current will trigger the limit
function. If the
1 V
output does not demand enough
current, it may be increased, but try to keep it as low
as possible (see 5.4 for why). Wait until the tempera-
ture of the circuit has stabilized. Error on the side of
drawing a slightly lower current than needed, depend-
ing on the sensitivity required (see below). Increase
the load gradually, and watch the error indicator LED
(D1).
If the default indication threshold set by
R21
is not
sensitive enough for your needs, solder in the
500 kΩ
RV5 and try the adjustment procedure below.
If this does not work, or if the default indication did
not work at all, solder in
RV5
and remove
R21
. This
provides a wider range of variation for the indication
threshold, at the cost of a coarser adjustment rate.
With the potentiometer
RV5
and the default resistor
R21
soldered on the board or not depending on your
needs, adjust the external load potentiometer until the
output is 2 –
10 mV
below the set voltage. If you intend
to use the supply only above about
5 V
, the lower the
better (you may even be able to remove
RV5
and wire a
short across
R21
for a bit more sensitivity). To complete
the calibration, adjust
RV5
to the barrier where
D1
just
barely lights, or perhaps flickers.
3
Table 1:
Electrical characteristics. The
mark indicates specifications which apply over the full operating
temperature range. Otherwise, specifications are at (junction) temperatures of 25 ◦C.
Parameter Conditions Min Typ Max Units
Input Voltage Vin 5.0 32.0 V
Output Voltage Vout Iload <Ilim 0.0 Vin −Vdo V
Dropout Voltage Vdo Iload =100 mA 1.21 V
Iload =1.5A 1.23 1.5 V
Internal Current Limit Imax Vin =5 V, Vset =0 V, Vout = −0.1 V 1.5 2.0 A
Iout Relative Error Iload =1.5A 0 6 11 %
Iout Operating Range Vout −40 V Vout +0.4 V V
Temp Absolute Error 0◦C≤TJ≤125◦C -10 10 µA
125◦C<TJ≤150 ◦C -15 15 µA
Ripple Rejection PSRR f=120Hz 75 90 dB
Vripple =0.5 Vpp,Iload =0.1A, f=10 kHz 75 dB
Vin =Vout(nom) +3V f=1 MHz 20 dB
Internal Load Iint 2 3 4 mA
4
5 Principles of Operation
5.1 The LT3081 linear regulator
All of the regulation that the power supply provides is
done by the LT3081, a rugged linear regulator IC. The
regulation circuitry is depicted in Figure 1. An internal
current source of
50 µA
allows the set voltage to be
configured with a single resistor
Rset
. In the power
supply,
Rset
is determined by the two potentiometers
RV2 and RV3.
If
Vout <Vset
, then the error amplifier will increase
the base voltage of the NPN transistor until the en-
tire Sziklai pair has
Vset
at its emitter. Similarly, the
base voltage will be suitably reduced if
Vout >Vset
. In
this way, the output voltage is regulated by a negative
feedback loop.
In practice, it may be difficult to stabilize such a
circuit constructed of discrete components against os-
cillation. Using an integrated circuit solution such as
the LT3081 allows us to have matched transistors at
close to the same temperature, as well as to take advan-
tage of the work done by previous engineers to make
the output voltage stable. We simply add on some addi-
tional capacitances (
C1
to
C4
and
C8
) to improve noise
characteristics, transcient performance, and stability
a bit more.
5.2 The internal load
Given the requirement that any circuitry used in the
power supply must function consistently over the en-
tire range of
Vin
, a simple resistor (as in the LT3081
datasheet) cannot be used as a means of meeting the
minimum load requirement of the LT3081. Instead,
the LM334 current source (
U4
) was used. With
R23
set to
22 Ω
, we expect about
3.1 mA
to be sunk from
−
+
Vin
50 µA
Rset
Vout
Figure 1:
The equivalent voltage regulation circuitry
inside the LT3081. The equivalent current regula-
tion circuitry is not depicted here or in the LT3081
datasheet.
the output of the power supply, which is well above
the minimum load requirement of the LM3081, over
temperature. Since we are manually nulling the offset
due to this current, it is allowable to use a common
through-hole
5 %
tolerance resistor for
R23
, but if your
application requires precise current limiting over a
wide and changing range of temperatures, a
1 %
or bet-
ter tolerance resistor should be used for added thermal
stability.
5.3 The Hot indicator circuit
To establish a precise voltage of
100 mV
over the entire
range of
Vin
, corresponding to a junction temperature
of
100 ◦C
, a
2.5 V
LM4040 voltage reference (
U1
) and
a voltage divider were used. The LM393 comparator
(
U3B
) compares the Temp output to this reference tem-
perature, and is configured to pull the open collector
output of the comparator low if the Temp output goes
above the reference. This connects the indicator LED
to ground. A LM317 (
U6
) configured as a current source
supplies a stable current to the LED over the full range
of
Vin
. Inspection of the circuit shows that errors in-
troduced by resistor tolerances and comparator input
offset currents and voltages will result in an absolute
error of at most
5◦C
. Furthermore, the comparator
operates without hysteresis, so the LED may flicker
when the actual and reference temperatures coincide.
For the purpose of a coarse temperature indication,
these undesirable characteristics are inconsequential.
5.4 The Vout error indicator circuit
The general configuration of the
Vout
error indicator
circuit is similar to that of the Hot indicator circuit,
described in Section 5.3. However, the error introduced
5
by that circuit is unacceptable for the purpose of dis-
playing the current status of regulation. Additionally,
we expect the output voltage to coincide precisely (to
within a few millivolts) with the set voltage. Without
any correction, the LED may reasonably indicate an
error indefinitely, or at least flicker, when the output
voltage is actually well-regulated.
The standard solution that one may propose is to
add hysteresis (in the form of a Schmitt trigger) to the
comparator. This will not work. A Schmitt trigger must
have an upper trigger threshold that lies above the set
voltage, but in the course of recovering from current
limiting, the output voltage may never overshoot the
set voltage. Thus the threshold will never be crossed,
and the error indicator may remain on indefinitely.
What is needed instead, is a small offset.
If the comparator recieved a set voltage that was,
say,
10 mV
below
Vset
, then the problem is solved. Hys-
teresis is not even needed, since most all causes for
a failure in regulation will not manifest as a steady
offset of
10 mV
. But how can we create such a small
offset over the entire range of
Vout
, especially when the
offset is comparable in size to all of the sources of error
involved? The main barriers to control that must be
addressed include
• Resistor tolerances,
• Loading of input sources,
• Comparator input offset voltage,
• Comparator input bias current,
• Comparator input offset current, and
• Noise.
Since the entire point of adding the offset is to al-
low for errors, we can deal with the comparator input
offset voltage and current by lumping in the effect of
their worst-case absolute errors with the error in regu-
lation. This increases the minimum offset needed from
that due to regulation, but only to about the
10 mV
stated before. However, we cannot increase the off-
set too much: at an output voltage of
1.00 V
, an offset
of
10 mV
already represents a
1 %
error in indication.
The aim is to keep this level of precision for set volt-
ages from
1.00 V
to
30.0 V
. If better precision than
about
10 %
is needed below about
100 mV
, the calibra-
tion procedure detailed in Section 4.8 may be done at
the necessary low voltage, at the cost of less realiable
indication at higher voltages of
10 V
to
30 V
, depending
on the configuration.
So how are we to obtain the offset? Since the in-
put bias current of the comparator may introduce er-
rors comparable to the offset, we can change perspec-
tive. The “error” that it introduces can in fact be used
−
+LM393
Vout
Roff
−+
Iin(+)Roff
Iin(+)
Vin
Figure 2:
Introducing a small voltage offset by exploit-
ing the input bias current of the LM393 comparator.
as the offset. The LM393 and many other common
differential-input analog devices such as the LM358
have PNP darlington pair input stages. This means
that any input bias current will flow out of the input
terminals, conveniently allowing us to place a resistor
on the noninverting input of the comparator to achieve
an offset in the correct direction. Since the noninvert-
ing input is connected to the low-impedance
Vout
, the
offset voltage introduced may be reliably predicted as
Iin(+)Roff
(see Figure 2). For the typical
Iin(+) =25nA
and
Roff =150kΩ
(
R21
), we obtain an offset of
3.8 mV
.
This should handle possible offsets due to comparator
input offset voltage and regulation of up to
3 mV
, and
more offset may be provided with a potentiometer as
described in Section 4.8.
But there is a problem with this circuit. Let’s take a
closer look at the input bias current. While datasheets
like that for the LM393 give the input bias current
at
0 V
common mode voltage, we must know it for all
common mode voltages up to
Vin
. The inputs to the
LM393 essentially consist of differential PNP Darling-
ton pairs, fed by a common current source at their emit-
ters and drained by a current mirror at their collectors;
standard stuff. Assuming active operation, a cursory
analysis models the path from
Vin
to the noninverting
input
V+
as consisting of some emitter-base or emitter-
collector voltage drops, with some resistances in be-
tween. That is,
Iin,(+)
is set by the much larger (about
300 times or so) current set by the current source at
the emitters.
TODO
6
1 2 3 4 5 6
1 2 3 4 5 6
A
B
C
D
A
B
C
D
Date:
KiCad E.D.A. kicad (5.1.2)-1
Rev: Size: A4
Id: 1/1
Title:
File: psu.sch
Sheet: /
A2019-06-01
Simple Lab Power Supply
OUT
1
Imon 10
TEMP 11
IN 12
IN 13
IN 14
IN 15
OUT 16
OUT
17
OUT
2
OUT
3
OUT
4
OUT
5
Ilim
6
SET
7
OUT
8
OUT 9
U2
LT3081
1
2 4
U4
LM334M R23
22R
Vout
Vout
Vout
5
1
23
4
SW1
SW_SP4T
5
1
23
4
SW2
SW_SP4T
R8
1R0 R9
2R2
R3
13R
R4
27R R5
68R R13
39R R14
100R
1 mA
2.5 mA
5 mA
10 mA
25 mA
50 mA
100 mA
1
2
3
RV2
500k
1
2
3
RV3
10k GND GND
Vin
R26
1k
Iout
TEMP
1 mV/°C
1
2J3
Binding posts
Vin
Vout
GND
GND
Vin
TEMP
Vin
GND
R20
1k
GND
12
U1
LM4040DBZ-2.5
TP2
Vout
TP1
Vin
TP5
Gnd
**
R19
24k
R17
1k5
R18
1M
GND
R21
150k
Vout
*** The combination of the divider on V- and the voltage increase into V+ due to input bias current
should provide adequate offset over the full range of Vin so that the output of the comparator is
stable, but does not false-trigger due to Vout regulation tolerance.
***
**
C4
10u
GND
**
C3
10u
*
**
*
*
** Ceramic X5R or X7R.
* 1% tolerance or better. 5-10% otherwise.
C1
0u1
3.118 mA
R16
390R
R1
1R8 R2
4R7 R10
1R0
R11
1R0 R12
1R0
R6
100R R7
180R
PWR_FLAG
PWR_FLAG
*
*
(Optional all *)
R25
10k
R24
10k
*
C2
0u1
1
-
2
+
3
U3A
LM393
+
5
_
6
7
U3B
LM393
V-
4V+ 8
Vin
JP1
Min Lim
Vout
JP2
No limit
JP3
Preload
GND
C5
0u1 GND
R15
4k7
R22
1k
1 2
SW3
Lever toggle
1
2
J2
Barrel_Jack
1
2
J1
Screw_Terminal_01x02
GND
Vin
**
1 mV/mA
ADJ
1
VO
2VI 3
U5
LM317L_TO92
D1
LED_RED
D2
LED_RED
C6
0u1
C7
0u1
GND
10-turn
(opt; omit switches)
1
2
3
RV1
100R
1
2
3
RV4
1k
1
2
3
RV5
500k
Trimmer
(opt)
GND
JP4Guard
JP5Guard
GND
** C8
0u1
R27
100R
Vin
ADJ
1
VO
2VI 3
U6
LM317L_TO92
R28
100R
GND
7
7 Printed Circuit Board Layers
8
9
10
11
12
13
14
15
16
17
Table 2: Bill of materials with collated items. There are 60 components total.
Item Qty Reference(s) Value LibPart Footprint
1 6 C1, C2, C5, C6, C7, C8 0u1 Device:C_Small Capacitor_THT:C_Disc_D5.0mm_W2.5mm_P2.50mm
2 2 C3, C4 10u Device:C_Small Capacitor_SMD:C_1206_3216Metric_Pad1.42x1.75mm_HandSolder
3 2 D1, D2 LED_RED Device:LED_ALT LED_THT:LED_D3.0mm
4 1 J1 Screw_Terminal_01x02 Connector:Screw_Terminal_01x02 TerminalBlock_MetzConnect:TerminalBlock_MetzConnect_Type094_RT03502HBLU_1x02_P5.00mm_Horizontal
5 1 J2 Barrel_Jack Connector:Barrel_Jack Connector_BarrelJack:BarrelJack_Horizontal
6 1 J3 Binding posts Connector_Generic:Conn_01x02 psu-foot:Binding Posts
7 1 JP1 Min Lim Device:Jumper_NO_Small Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical
8 1 JP2 No limit Device:Jumper_NO_Small Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical
9 1 JP3 Preload Device:Jumper_NO_Small Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical
10 2 JP4, JP5 Guard Device:Jumper_NO_Small psu-foot:Guard_Jumper
11 1 R1 1R8 Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
12 1 R2 4R7 Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
13 1 R3 13R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
14 1 R4 27R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
15 1 R5 68R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
16 2 R6, R14 100R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
17 1 R7 180R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
18 4 R8, R10, R11, R12 1R0 Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
19 1 R9 2R2 Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
20 1 R13 39R Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
21 1 R15 4k7 Device:R Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
22 1 R16 390R Device:R Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
23 1 R17 1k5 Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
24 1 R18 1M Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
25 1 R19 24k Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
26 2 R20, R26 1k Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
27 1 R21 150k Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
28 1 R22 1k Device:R Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
29 1 R23 22R Device:R Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
30 2 R24, R25 10k Device:R Resistor_SMD:R_1206_3216Metric_Pad1.42x1.75mm_HandSolder
31 2 R27, R28 100R Device:R Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
32 1 RV1 100R Device:R_POT_US psu-foot:Trim_pot_Bourns_TC33X-2-101E
33 1 RV2 500k Device:R_POT_US Potentiometer_THT:Potentiometer_Piher_PC-16_Single_Horizontal
34 1 RV3 10k Device:R_POT_US Potentiometer_THT:Potentiometer_Piher_PC-16_Single_Horizontal
35 1 RV4 1k Device:R_POT_US Potentiometer_THT:Potentiometer_Piher_PC-16_Single_Horizontal
36 1 RV5 500k Device:R_POT_US psu-foot:Trim_pot_Bourns_TC33X-2-101E
37 2 SW1, SW2 SW_SP4T psu-sch:SW_SP4T psu-foot:SP4T_CK_SK-14D01-G-6
38 1 SW3 Lever toggle Switch:SW_SPST psu-foot:SW_SPST_Lever_Rubber
39 1 U1 LM4040DBZ-2.5 Reference_Voltage:LM4040DBZ-2.5 Package_TO_SOT_SMD:SOT-23
40 1 U2 LT3081 psu-sch:LT3081 Package_SO:HTSSOP-16-1EP_4.4x5mm_P0.65mm_EP3.4x5mm_Mask3x3mm_ThermalVias
41 1 U3 LM393 Comparator:LM393 Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
42 1 U4 LM334M Reference_Current:LM334M Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
43 2 U5, U6 LM317L_TO92 Regulator_Linear:LM317L_TO92 Package_TO_SOT_THT:TO-92_Inline
18

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