Leader LTC-905 User manual

LEADER
CURVE TRACER
INSTRUCTION MANUAL

TABLE OF CONTENTS
Page
1. DESCRIPTION . 1
2. SPECIFICATIONS . 1
3. CONTROLS AND CONNECTORS . 1
4. OPERATION
4.1 Preliminary Notes . 3
4.2 Preparation . 5
4.3 Transistor Measurements .. 5
4.3.1 NPN, low level . 5
4.3.2 NPN, power type . 6
4.3.3 PNP, low level . 6
4.3.4 PNP, power type . 6
4.3.5 Measurement of hpg .. 7
4.4 Measurement of FET’s.. .. 8
4.4.1 N-cEannel FET, and N-channel MOS FET.. 8
4.4.2 P-channel FET, and P-channel MOS FET . 8
4.4.3 Mutual conductance, gm, measurement .. 8
4.4.4 Enhancement type FET measurement . 9
4.5 Diode Measurements
4.5.1 Standard test condition . 9
4.5.2 General purpose: Power rectifiers, detectors .10
4.5.3 Zener diodes .....10
4.5.4 Tunnel diodes ...10
4.5.5 Quantitative diode measurements ...10
4.6 SCR (Thyristor) Measurements.H
4.7 UJT (Unijunction transistor) Measurements. j j
5. Measurements with External Bias
5.1 General... 12
5.2 Transistor Measurements .... 12
5.2.1 Bias supplies . 12
5.2.2 hpg measurements.
5.2.3 IcEO measurements . jg

5.3 F ET Measurements.. . . . .. 2 3
5.3.1 Bias supplies .13
5.3.2 gm' measurements . 1 4
5.3.3 Pinch-off Voltage, Vp, measurement .-.14
5.3.4 Drain current, measurement.15
6. In-Circuit Testing...j 5
6.1 General..
6.1.1 Application .15
6.1.2 Use of In-Circuit Probe, LP-11 .15
6.2 Display of Defective Transistors, FET .16
6.3 Notes on In-Circuit Testing .17
7. MAINTENANCE.18
7.1 Removing the Panel from Case.18
7.2 Fuse Renewal.18
7.3 AC Input Connections.18

1.
DESCRIPTION
Curve tracing on a scope is made easy with the LTC-905. Characteristic curves of all types of
semiconductors can be accurately displayed. This is far superior to the conventional ohmmeter
checks for quality. In-circuit testing is possible for quick checks.
Two inputs are provided which enable comparison of two similar units.
LTC-905 is designed to test the following:
1. Transistors - NPN, PNP, FET and MOS FET.
2. SCR’s (Thyristors) and Triacs.
3. Diodes - rectifier, detector, zener and tunnel.
2. SPECIFICATIONS
Collector/Drain Sweep
Frequency
Voltage
Sweep Waveform
Current
Current Limiter
Step Generator
No. of Steps
Current per Step
Volt per Step
External Bias
Power Requirements
Size and Weight
Accessories
120Hz, or 100Hz (2 x line frequency).
8 steps: 10, 20, 30, 40, 50, 60, 80 and 100V; accuracy, ±10%.
(Rated voltage)
Fullwave rectified.
100mA, maximum.
100012 for low level transistors;
100S2 for power transistors.
7.
10, 20, 50/iA; 0.1, 0.2, 0.5, 1, 2mA; accuracy, ±5%.
0.1, 0.2, 0.5V; accuracy, ±5%.
One curve display.
100, 120, 200, 220, or 240V, 50/60Hz,
25VA maximum operating, and 6VA at standby.
240(W)X 90(H)X 170(D) mm, 2kg, (9^”X 3>f X 6K”; 4.5 lbs.)
Instruction manual . 1
3-lead cable (banana plugs/clips) . 2
Scope leads, 2 red and 1 black .1 set
In-circuit test probe, LP-11 . 1
3. CONTROLS AND CONNECTORS
®
POWER switch
Turns on the AC power.
(D
Pilot lamp
Indicates when AC power is on.
(D
POLARITY switch
Selects the mode of operation.
©
VERTICAL jacks Connections to vertical scope input.
©
EXT. BIAS jack
Connection to an external source to apply base or gate bias
for a one curve display.
i

© BASE CURRENT/
GATE VOLTAGE
switch
(7) Banana plug jacks
® TO-5 socket
© SELECTOR, lower
© SELECTOR, upper
© TO-5 socket
@ Banana plug jacks
@ COLLECTOR/DRAIN
SWEEP VOLTAGE
switch
@ CURRENT LIMIT
switch
© H. LENGTH control
@ HORIZONTAL jacks
Sets the bias current in eight steps and gate voltage in three
steps; provided with position for external bias.
One group for test lead connections:
Color ; Transistor
FET
Blue C - Collector D- Drain
Green
B - Base
G - Gate
Yellow
! E - Emitter
S - Source
For insertion of transistor under test.
Selects input at “A” or “B” side. At OFF, both sides are
disconnected.
Setting depends on type of transistor, NPN or PNP at
TRANS; MOS FET and FET at FET.
Same as ® .
Same as (7) .
With eight positions for setting the sweep voltage.
Set at SIGNAL for low level types and at POWER for power
types.
Adjusts the amplitude of the horizontal sweep on the scope.
Connections to horizontal scope input.
o

4. OPERATION
4.1 Preliminary Notes
A. A C Line Voltage.
The AC voltage for operation should be kept within ±10% of the rated value, see
CHART 1. When low, the performance will be affected; when high, damage may result
to circuit, components in the instrument.
CHART 1
Rating, V Range, V
Fuse
100
90 - 110
120
108 - 132
200
180 - 220
0.5A
220
198 - 242
240
216 - 264
The line fuse is 0.5A for all voltages.
Refer to Sect. 7.3 for primary connections when different voltages are used.
B. A C Input Phasing.
Unless the phase of the AC voltage to the LTC-905 and scope
are in proper relation, “double curves” will be displayed, see
Fig. 4-1. This can be corrected by reversing the AC plug connection
on the scope or LTC-905.
NOTE: When the scope is not provided with the DC input
to the horizontal amplifier, the proper display may not
be obtained.
Fig. 4-1 Double curve effect,
AC phasing not proper.
C. Collector or Drain Sweep Application.
In order to protect the transistors and diodes against damage, care must be taken in
application of the sweep voltage.
Voltages over 10V should not be used unless specially noted.
D. Scope Characteristics
The scope for curve tracing is used as an X-Y scope. It is necessary that the scope
satisfies the conditions in CHART 2.
3

CHART 2
i
Amplifier
Bandwidth '
i
Sensitivity,
minimum
Vertical
DC - 1kHz or higher
0.1V/cm, or /div.
Horizontal
DC, or AC - 1kHz or higher
lV/cm, or /div.
In quantitative measurements, particularly for hpp and g m , a scope with the vertical
gain calibrated in V/cm should be used. For ease in readouts, the V/cm sensitivities
converted to the most used mA/cm calibration at two settings of the CURRENT LIMIT
switch are listed in CHART 3.
CHART 3
Vertical
Sensitivity
CURRENT LIMIT Setting
SIGNAL
POWER
i
50mV/cm
0.5mA/cm
5mA/cm
0.1 V/cm
1 mA/cm
10m A/cm
0.2V/cm
! 2mA/cm
i 20mA/cm
0.5V/cm
! 5mA/cm
! 50mA/cm
By adjusting the H. LENGTH control for the trace to cover 10cm, the V/cm unit
horizontally can be correlated with the sweep voltage setting.
E.
Scope Connections and Settings.
Connections between the scope and LTC-905 are made with the three leads as
indicated in Fig. 4-2, red leads to vertical and horizontal inputs and black lead to
common ground.
Set the vertical gain initially at lOOmV/cm and the AC-DC
switch at DC.
Set the horizontal gain at maximum and the AC-DC
switch at DC (use AC coupling if DC is not provided).
4

4.2 Preparation
Switch settings:
POWER
CURRENT LIMIT
COLLECTOR/DRAIN
SWEEP VOLTAGE
BASE . GATE
CURRENT'VOLTAGE
SELECTOR: upper
lower
OFF.
SIGNAL.
10 V.
EXT BIAS
Type under test, TRANSistor or FET.
OFF.
Connections:
With proper attention to the terminals, the transistor is connected to the socket or
leads from the three jacks at “A” or “B” side. When comparing two units, use the
sockets and lead connections at both sides.
4.3 Transistor Measurements
4.3.1 NPN, low level.
Switch settings:
BASE CURRENT
COLLECTOR SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
10 (lA.
10V.
NPN.
SIGNAL.
TRANS.
A or B, as connected.
The scope controls are adjusted for suitable display and proper positioning, see Fig. 4-3
and Fig. 4-4. Seven curves will be observed with Si transistors and eight curves with Ge
transistors. This serves as a check.
When the BASE CURRENT is set at 20juA, the height will be doubled.
The transistor can be said to be satisfactory when the curves are displayed as shown in the
figures.
5

4.3.2 NPN, power type.
For NPN power transistors, under the same conditions as in Sect. 4.3.1, set the CURRENT
LIMIT at POWER and BASE CURRENT at 0.1 up to 1mA.
As the COLLECTOR SWEEP VOLTAGE is gradually raised from 10V upward.
Do not increase the sweep voltage beyond the point where
the curves start to bend, the curves will be as shown in Fig. 4-5.
The region of the breakdown voltage can be read off.
For example, with the sweep voltage at 50V, adjust the H.
LENGTH control for the sweep to cover 10cm horizontally,
Fig. 4-5 Power transistor ° r 5V/cm ’ in this case - The collector-emitter voltage, V CE ,
„> can be read easily,
curves. The curves 1
start to bend.
By adjusting the H. LENGTH control for the trace to cover 10cm (or div.), the V/cm unit
can be correlated with the voltage settings.
NOTES. 1. When the sweep voltage and/or base current are increased, the transistor
will become heated.
2. Power transistors should be tested within as short a time as possible. This
will prevent overheating when the sweep voltage is over 10V and/or
when a large base current is flowing.
4.3.3 PNP, low level.
Switch settings:
BASE CURRENT
COLLECTOR SWEEP
POLARITY
CURRENT LIMIT
SELECTOR: upper
lower
10/uA.
10V.
PNP.
SIGNAL.
TRANS.
A or B, as connected.
The curve tracing procedure is the same as given in Sect. 4.3.1.
The curve display will be as shown in Fig. 4-6.
Fig. 4-6 PNP transistor
curves.
4.3.4 P NP, power type.
Set the switches as in Sect. 4.3.2 above with the following exception:
POLARITY at PNP.
The curve tracing procedure is the same as described for NPN power transistors. The same
care must be exercised to prevent overheating with high sweep voltages and base currents.
6

4.3.5 Measurement of hpg.
Measurement of h FE for an NPN transistor will be given; for the PNP type, the only
changes will be in the setting of the POLARITY switch at PNP instead of NPN Ind in the
direction of the curves.
The DC current amplification of a transistor is given by the relation -
Collector current, Ip
h FE = ---
Base current, Ig
For this measurement, a calibrated scope is required.
Referring to CHART 3 (Sect. 4.1, Parag. D) under SIGNAL of CURRENT LIMIT, the
vertical gain is set at O.lV/cm. Under this condition, the collector current is read off at ImA/cm.
With the Si transistor, seven typical curves for Ig in lOfiA steps from 0 to 60/iA are shown
in Fig. 4-7. On the 60/tA curve, I c = 4.2mA. By calculation,
h FE = 4.2 x 10' 3 / 60 x 10* 6 = 70.
In Fig. 4-8, curves for a typical Ge transistor are shown. From the I fi = 70/1 A, I c = 2.1mA
and hpg = 30.
Fig. 4-8 hp E measurement,
Ge transistor.
In the two examples given above, hpg measurements are collector-emitter voltage, V^g =
10V. Other measurements can be made when required with the sweep voltage at 20, 30V,
etc.
For hpg of power transistors, set the CURRENT LIMIT switch at POWER and the
POLARITY switch at NPN or PNP as required.
The scope sensitivity is set by reference to the POWER column of CURRENT LIMIT in
CHART 3.
For example, with the sensitivity at 0.2V/cm, the calibration will be 20mA/cm. By setting
the BASE CURRENT at 0.2mA, and SWEEP VOLTAGE at 50V (10cm length), curves in
Fig. 4-9 will be displayed. From the figure, Ig = 1.2mA and I c = 50mA.
Thus, hpg is approximately 41.7. Measurements of hpg
in this manner will be accurate within +10%.
For higher accuracy, use an external bias supply; details are
given in Sect. 5.
Fig, 4-9 hpg measurement,
power transistor.
7