TTI CPX200 Service Manual
CPX200
Dual 35V 10A
Power Supply
Service Manual
Book Part Number 48511-0270 - Issue 1
Table of Contents
Specifications 2
Safety 4
EMC 5
General 6
Circuit Descriptions 7
Calibration 12
Parts List 14
Component Layouts 22
Circuit Diagrams 25
1
Specifications
OUTPUT SPECIFICATIONS
Voltage Range: 0V to 35V
Current Range: 0A to 10A
Power Range: Up to 175W
Output Voltage Setting: By coarse and fine controls.
Output Current Setting: By single logarithmic control.
Operating Mode: Constant voltage or constant current with automatic cross-over
provided that the power demanded stays within the power
envelope, see graph. Outside of this envelope the output becomes
unregulated.
Output Switch: Electronic. Preset voltage and current displayed when off.
Output Terminals: 4mm terminals on 19mm (0·75”) pitch. 15A max.
Sensing: Remote via 4mm terminals or direct via shorting links (provided).
Output Impedance:
Typically <5mΩ in constant voltage mode.
Typically >5kΩ in constant current mode (voltage limit at max).
Output Protection: Forward protection by Over-Voltage Protection (OVP) trip;
maximum voltage that should be applied to the terminals is 50V.
Reverse protection by diode clamp for reverse currents up to 3A.
OVP Range: 10% to 110% of maximum output voltage set by front panel
screwdriver adjustment.
Load & Line Regulation: <0.01% of maximum output for a 90% load change or 10% line
change.
Ripple & Noise
(20MHz bandwidth):
5mVrms max; typically <2mVrms, <20mV pk-pk, both outputs fully
loaded (7A @ 25V), CV mode.
Transient Load Response: <2ms to within 100mV of set level for 90% load change.
Temperature Coefficient: Typically <100ppm/°C
Status Indication: Output on lamp.
Constant voltage mode lamp.
Constant current mode lamp.
Unregulated (power limit) lamp
Trip message on display.
2
METER SPECIFICATIONS
Meter Types: Dual 4 digit meters with 12.5mm (0.5") LEDs. Reading rate 4 Hz.
Meter Resolutions: 10mV, 10mA
Meter Accuracies: Voltage 0.2% of reading +/-1 digit,
Current 0.5% of reading +/-1 digit
GENERAL
AC Input: 230V AC ± 14%, 50/60Hz. Installation Category II.
Power Consumption: 600VA max.
Operating Range: +5ºc TO +40ºC, 20% TO 80% RH.
Storage Range: -40ºC to + 70ºC.
Environmental: Indoor use at altitudes up to 2000m, Pollution Degree 1.
Safety: Complies with EN61010-1.
EMC: Complies with EN50081-1 and EN50082-1.
Size: 210 x 130 x 350mm (WxHxD) half rack width x 3U height
(optional rack mounting kit available).
Weight: 5kg
3
Safety
This power supply is a Safety Class I instrument according to IEC classification and has been
designed to meet the requirements of EN61010-1 (Safety Requirements for Electrical Equipment
for Measurement, Control and Laboratory Use). It is an Installation Category II instrument
intended for operation from a normal single phase supply.
This instrument has been tested in accordance with EN61010-1 and has been supplied in a safe
condition. This instruction manual contains some information and warnings which have to be
followed by the user to ensure safe operation and to retain the instrument in a safe condition.
This instrument has been designed for indoor use in a Pollution Degree 1 environment (no
pollution, or only dry non-conductive pollution) in the temperature range 5°C to 40°C, 20% - 80%
RH (non-condensing). It may occasionally be subjected to temperatures between +5° and -10°C
without degradation of its safety.
Use of this instrument in a manner not specified by these instructions may impair the safety
protection provided. Do not operate the instrument outside its rated supply voltages or
environmental range. In particular excessive moisture may impair safety.
WARNING! THIS INSTRUMENT MUST BE EARTHED
Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.
When the instrument is connected to its supply, terminals may be live and opening the covers or
removal of parts (except those to which access can be gained by hand) is likely to expose live
parts. The apparatus shall be disconnected from all voltage sources before it is opened for any
adjustment, replacement, maintenance or repair. Capacitors inside the power supply may still be
charged even if the power supply has been disconnected from all voltage sources but will be
safely discharged about 10 minutes after switching off power.
Any adjustment, maintenance and repair of the opened instrument under voltage shall be avoided
as far as possible and, if inevitable, shall be carried out only by a skilled person who is aware of
the hazard involved.
If the instrument is clearly defective, has been subject to mechanical damage, excessive moisture
or chemical corrosion the safety protection may be impaired and the apparatus should be
withdrawn from use and returned for checking and repair.
Make sure that only fuses with the required rated current and of the specified type are used for
replacement. The use of makeshift fuses and the short-circuiting of fuse holders is prohibited.
Do not wet the instrument when cleaning it.
The following symbols are used on the instrument and in this manual:-
Earth (ground) terminal.
mains supply OFF.
l
mains supply ON.
alternating current (ac)
direct current (dc)
4
EMC
This power supply has been designed to meet the requirements of the EMC Directive
89/336/EEC.
Compliance was demonstrated by meeting the test limits of the following standards:
Emissions
EN50081-1 (1992) Generic emission standard for residential commercial and light
industry. Test methods and limits used were:
a) EN55022 Conducted, Class B
b) EN55022 Radiated, Class B
Immunity
EN50082-1 (1992) Generic immunity standard for residential, commercial and light
industry. Test methods and limits used were:
a) EN60801-2 (1993) Electrostatic Discharge, 8 kV air discharge.
b) IEC801-3 (1984) RF Field, 3 V/m.
c) IEC801-4 (1988) Fast Transient, 1 kV peak (AC line) and 0.5kV peak (DC outputs).
Note that electrostatic discharge direct to the output terminals will not damage the instrument but
may trip the Overvoltage Protection (OVP), turning the output off, see Protection section.
Note also that if the power supply is operated in a high RF field, the RF signal will be picked up
on unscreened leads between the supply and the load. If the load is likely to be sensitive to such
signals, connect it to the supply using screened leads.
Cautions
To ensure continued compliance with the EMC directive the following precautions
should be observed:
a) after opening the case for any reason ensure that all signal and ground connections
are remade correctly before replacing the cover. Always ensure all case screws are
correctly refitted and tightened.
b) In the event of part replacement becoming necessary, only use components of an
identical type, see the Service Manual.
5
General
Service Handling Precautions
Service work or calibration should only be carried out by skilled engineers using high quality test
equipment. If the user is in any doubt as to his competence to carry out the work, the instrument
should be returned to the manufacturer or their agent overseas for the work to be carried out.
The tracks on the printed circuit boards are very fine and may lift if subjected to excessive heat.
Use only a miniature temperature-controlled soldering iron and remove all solder with solder wick
or suction before attempting to remove a component.
Dismantling the instrument
WARNING
Disconnect the power supply from all voltage sources before it is opened for adjustment or repair.
Capacitors inside the supply may still be charged even if the supply has been disconnected from
all voltage sources but will be safety discharged about 10 minutes after removing power.
If any adjustment or repair of the opened supply under voltage is inevitable it shall be carried out
only be a skilled person who is aware of the hazard involved. The incoming AC supply to the unit
under test should be isolated for safety by means of a 1:1 isolation transformer of at least 700VA.
High voltages (up to 400V) are always present in the primary-side circuitry which lies in a clearly
defined area at the rear of both the upper (control) and lower (main) printed circuit boards.
Removing the link at PJ10 only disconnects HV from the power FETs Q1/Q2 (Q101/Q102).
1. Remove the six screws retaining the top cover.
2. To remove the upper (control) pcb proceed as follows.
Unplug the 26-way flat cables to the front panel pcb and the 16-way flat cables to the
lower (main) pcb noting their orientation (red stripe to pin 1 corner markers on pcb).
Unplug the harnesses from the 50Hz transformer (PJ7, PJ107) and the control
connections to the main board (PJ5, PJ105) noting the orientation of the sockets (pin 1 on
the socket housing to pin 1 corner markers on pcb).
Remove the 4 self-tap screws and lift off the pcb.
3. To remove the lower (main) pcb proceed as follows. Remove the power (M3 nuts) and
sense (2-way header) connections to the front panel for both channels noting orientation;
inner (insulated) power lead is positive, red sense lead to corner marker on pcb.
Unplug the two harness connections from the 50Hz transformer (PJ1 and PJ8) and the
connection from the front panel switch (PJ6), noting orientation (pin 1 on the socket
housing to pin 1 corner markers on pcb). Remove the safety earth connection to the rear
panel; remove the rear panel (3 screws). Remove the 9 screws which secure the main pcb
support pillars to the case lower (i.e. the screws accessible underneath the case lower)
and lift the pcb clear with its mounting pillars attached.
4. To remove the front panel pcb, first remove the six push-on control knobs then undo the 5
screws securing the pcb to the front panel and lift free.
5. Reassemble in the reverse order taking great care to ensure that all connections are
exactly as before dismantling and that no insulation creepage and clearance distances
have been compromised. Ensure that only the correct fastenings are used otherwise
earthing, and hence EMC and safety performance, may be impaired.
6
Circuit Descriptions
The two outputs are identical with the exception of slight layout variations; only one output
(Channel A) is therefore described. Component positions on the other output (Channel B) are
numbered from 101 upwards, e.g. C22 on Channel A described is C122 on Channel B.
Power Section
The power section is contained entirely on the main (lower) board; refer to the main pcb
schematic.
Each output is configured as a double-ended half-bridge operating in continuous flyback mode to
reduce switching currents in the power FETs and output diodes; both converters operate from a
common high voltage (rectified mains) supply.
The secondary power limit is determined by the primary current limit which gives rise to a linear
characteristic (between maximum current and maximum voltage) rather than a parabolic
characteristic associated with a true ‘constant power’ limit, see Specification section.
Mains Input, Filtering and Rectification
The AC input to the supply is direct via a pcb-mounted IEC inlet connector. Components C9, L3,
L4, and C5-C8 comprise an input filter which ensures that the supply meets both conducted
emission and conducted immunity EMC requirements. VDR1 ‘clips’ mains spikes for component
protection; R3 provides safety discharge for C9, C5 and C8.
Pcb-mounted fuse FS1 limits damage on switchmode failure; the front panel mains switch is
connected via PJ6; RT1 reduces the mains inrush current when the unit is turned on from cold.
BRI is a bridge rectifier and C1, C2 the reservoir capacitors for the high voltage rail which is
linked at PJ10 to VBULKA and VBULKB of Channel A and Channel B respectively. L1 and L2
reduce current spikes caused by the switching of the FETs. BR1 and C1, C2 can also be
configured as a voltage doubler for 115VAC operation by fitting the header into PJ1B instead of
PJ1A; however, for operation up to full power (350W) L3 and L4 must be changed to 8Amp
components. PJ1 is also the point from which mains power is fed to the auxiliary mains
transformer.
Operation of the Double-ended Half-bridge
A simplified version of the power switching stage is shown below.
When FETs Q1 and Q2 are turned on, current flows in the primary winding of power transformer
T1, storing energy in the primary inductance; D3 and D4 are reverse-biased so no current flows in
7
the secondary. When Q1 and Q2 are turned off the voltage across the primary will reverse and
generally bring diodes D1 and D2 into conduction; D1, D2 provide clamp protection against
overvoltage caused by leakage inductance in the transformer, so protecting the FETs. At the
same time the secondary e.m.f. generated will cause current to flow through D3, D4 into C14 and
the load; as soon as this starts to happen current will cease to flow through D1 and D2 and the
energy stored in the primary is transferred to the secondary.
Zener diodes D7 and D8 protect the FETs in the event of a voltage surge and protect the drive
circuit in the event of a FET failure.
FET Drive Circuit
IC1 is an IR2110 drive IC which has the necessary on-chip isolation (500V) to be able to drive
both FETs. The FETs need 15V gate drive. The 15V supply for Q2 is generated from the auxiliary
mains transformer via BR2 and IC16; this rail also powers all the ground-referenced control
circuitry on the primary side, including the UC3846. Q1 needs an isolated supply which is
generated from an extra winding on the power transformer in phase with the secondary; D5 and
C23 rectify and smooth the transformer output, dropper resistor R15 and 15V zener D9 regulate
the rail.
Until the FETs start switching no 15V supply for Q1 is generated. To overcome this R21 is used to
charge C23 at start-up; when VBULKA reaches about 150V there is enough voltage on C23 to
turn on the high rail of IC1 and maintain the FET in an oscillating mode independent of output
loading. If for any reason this rail should drop below 8V, IC1 will switch off, thus maintaining a
good enhancement voltage across the gate at all times.
R8, C10 and R9, C11 are snubber networks for Q1 and Q2 respectively.
Output Filtering
Large switching spikes caused by the switching of FETS Q1, Q2 and rectifying diodes D3, D4 are
filtered by the output stage to bring both differential noise and common mode noise into
specification.
Snubber network R10, C13 reduces noise generated by the output diodes.
L5 and C16 comprise the main differential filter; R16 damps any ringing in the filter. R13, R17 and
R20 are a small pre-load, ensuring voltage loop control with no external load and providing some
load for the L5, C16 filter. The common mode filter L7, C15/C27 further reduces differential noise.
Common-mode noise is minimised by the low capacitance design of power transformer and is
attenuated by C17, C18; R19 provides a discharge path for these capacitors when the output
terminals are floated from ground. Solid ground connections at E1 and E2 are essential for good
common-mode noise performance.
The front panel mounted components LLA, CAA and CAB provide both differential and commonmode attenuation at high frequencies (>2MHz); HF differential noise is attenuated by the leakage
inductance of LLA with CAB and HF common-mode noise is attenuated by LLA and CAA.
8
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