Webinar: High Voltage Fiber Optic (HVFO) Probe for Small Signal Floating Measurements

WEBINAR: High Voltage Fiber Optic Probe

June 21st, 2017Thank you for joining us. We will begin at 2:00pm EDST. NOTE: This presentation includes Q&A. We will be taking questions during the presentation with answers at the end using the questions section of your control panel

June 21, 2017 1

Teledyne LeCroy Overview

June 21, 2017 2

LeCroy was founded in 1964 by Walter LeCroy Original products were high-speed digitizers for

particle physics research

Corporate headquarters is in Chestnut Ridge, NY

Long history of innovation in digital oscilloscopes First digital storage oscilloscope Highest bandwidth real-time oscilloscope

(100 GHz) World’s only 12-bit, 1 GHz, 8ch oscilloscope

LeCroy became the world leader in protocol analysis with the purchase of CATC and Catalyst Frontline Test Equipment and Quantum Data

were also recently acquired (2016)

In 2012, LeCroy was acquired by Teledyne Technologies and renamed Teledyne LeCroy

• Product Manager with Teledyne LeCroy for over 15 years

• B.S., Electrical Engineering from Rensselaer Polytechnic Institute

• Awarded three U.S. patents for in the field of simultaneous physical layer and protocol analysis

Ken JohnsonDirector of Marketing, Product ArchitectTeledyne [email protected]

June 21, 2017 3

About the Presenter

Agenda

Probe Types and Characteristics Probe Fit to Various Applications Highly Relevant Probe Specifications HVFO103 Product Overview HVFO103 Probing Comparisons Summary Questions

June 21, 2017 4

Probe Types and CharacteristicsHigh voltages present in power electronics requires care in selecting a probe that is safe to use. But just because a probe is safe to use does not mean that it will provide a good measurement result.

June 21, 2017 5

High Voltage Probes Commonly Used in Power Electronics

High Voltage “Isolated”

1. Passive, Single-ended

2. Active, Single-ended (fiber-optic isolated)

3. Active, Differential (conventional high attenuation)

4. Active, Differential Amplifier with matched probe pair (conventional high attenuation)

1 2

3 4

PPE or HVP Series

HVFO103

HVD or ADP SeriesDA1855A + DXC100A

June 21, 2017 6

1 - High Voltage Passive Single-ended Probes

Parameter ValueBandwidth 500 MHzVoltage Range (SE)Voltage Range (DM)Voltage Range (CM)

Up to 6kV typicalN/AN/A

Voltage Offset N/ALoading 10MΩ || 7.5pF

ZIN=50Ω@500 MHz

Attenuation 100xCMRR N/A

A good option for some, but also have high attenuation values (so more noise)

June 21, 2017 7

2 - High Voltage Active Single-ended (Fiber Optic) Probes

A new topology specifically for measuring small signals floating on a HV DC bus


2 to 80VN/AVirtually Unlimited

Voltage Offset N/ALoading 1-10MΩ || 34-22pF

ZIN=50kΩ@100 kHz

Attenuation 2x to 80xCMRR >140 dB

June 21, 2017 8

3 - High Voltage Active Differential Probes

Excellent all around choice for many applications, but has its limitations

Some models perform better than others

Parameter ValueBandwidth ~100 MHzVoltage Range (SE)Voltage Range (DM)Voltage Range (CM)

N/A2kV to 8kV1kV to 6kV

Voltage Offset 1kV to 6kVLoading 10MΩ || 2.5pF

ZIN=1kΩ@100 MHz

Attenuation 50-2000xCMRR 65 dB (HVD)

June 21, 2017 9

4 - High Voltage Active Differential Amplifier with Matched Probe Pairs

Exceptional overdrive recovery and fine offset adjust make this idea for device conduction loss and switching loss testing, and measuring small signal sensor values floating on a HV DC bus.


N/A0.5V to 2.5kV155V to 2.5kV

Voltage Offset Depends on probeLoading Depends on probeAttenuation 1-1000x, with gainCMRR 100 dB

June 21, 2017 10

Polling Question #1

What types of probes do you use? (select one or more answers) High Voltage Passive Single-ended Probes High Voltage Active Single-ended (Fiber Optic) Probes High Voltage Active Differential Probes High Voltage Active Differential Amplifier with Matched Probe Pairs

June 21, 2017 11

Probe Fit to Various ApplicationsSome probes perform better than others in certain applications, and some should never be used when high voltage signals are being measured.

June 21, 2017 12

Color Code for the Application Tables that FollowThis is the perfect probe for the application. There are few issues with its use, and it has been optimized in price and performance for this application.

There are some compromises in performance of the probe in this application, though some users may find the probe works fine for them.

While the probe will provide a result and will not be damaged in making the measurement, most users would find the probe does not work well in this application.

The probe should absolutely not be used in this application as damage to the probe, oscilloscope or device under test (DUT) may occur, or harm may come to the operator.

June 21, 2017 13

Probe to Power Electronics Application Fit for 170-1000Vdc Bus/Link (120/240Vac – 600Vac Class)

170-1000Vdc Bus/Link

Low Voltage Probes High Voltage ProbesPassive

Single-endedActive

Single-endedFET-type

(VCM<VDCbus)

Active Single-ended

Rail-type(RP4030)

ActiveDifferential(VCM<VDCbus)

PassiveSingle-ended (PPE or HVP

Series)

ActiveSingle-ended

fiber optic(HVFO103)

ActiveDifferential (high-atten)

(HVD Series)

ActiveDiff Amp w/ Probe Pair(DA1855A)

Appl

icat

ion

/ Sig

nal T

ype

/M

easu

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ent L

ocat

ion

Pow

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Sem

icon

duct

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e Gate Drive Best solution Example 2, 4

May be OKExample 1,2,4

Maybe, expensiveExample 2

Conduction Loss Example 5 Best solution Example 5

Switching Loss Example 6 Best solution in all cases

Sen

sing

or

Dis

cret

e C

ompo

nent

s Series/Shunt Resistor <1V can be noisy <1V can be noisy,worse CMRR

Best solution in all cases

Sensor Signal Best solution Example 7

Loading, noise issuesExample 7 May be loading issues

Discrete Components Best solution in all cases May be loading issues

Sys

tem

Inpu

ts/O

utpu

ts

Line Side (AC) InputLine-neutral voltage probing only, high

attenuation


Expensive, more capability than

required

DC Bus/Link High attenuation,could be noisy



required

Inverter/Drive PWM Output

Line-reference voltage probing only,

high attenuation



required

DC-DC Converter HV Input/Output

High attenuation, could be noisy

Limited voltage range, expensive



required

DC-DC Converter LV Output (Power Rail) Not Applicable

June 21, 2017 14

Probe to Power Electronics Application Fit for 1500Vdc Bus/Link (Grid-tied Solar PV Inverters)

1500Vdc Bus/Link


Single-endedActive


(VCM<VDCbus)

Active Single-ended

Rail-type(RP4030)



Series)

ActiveSingle-ended



(HVD Series)


Appl

icat

ion

/ Sig

nal T

ype

/M

easu

rem

ent L

ocat

ion

Pow

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Sem

icon

duct

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evic

e Gate Drive Best solution May be OK May be OK, expensive

Conduction Loss Best solution

Switching Loss Best solution in all cases

Sen

sing

or

Dis

cret

e C

ompo

nent



Sensor Signal Best solution Loading, noise issues May be loading issues


Sys

tem

Inpu

ts/O

utpu

ts


attenuation



required




required



high attenuation



required






required


June 21, 2017 15

Probe to Power Electronics Application Fit for >1500Vdc Bus/Link (Medium Voltage 5kV Class Apparatus)

>1500Vdc Bus/Link


Single-endedActive


(VCM<VDCbus)

Active Single-ended

Rail-type(RP4030)



Series)

ActiveSingle-ended



(HVD Series)


Appl

icat

ion

/ Sig

nal T

ype

/M

easu

rem

ent L

ocat

ion

Pow

er

Sem

icon

duct

orD

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e Gate Drive Best solution May be OK – 6 kV CM voltage rating

2500V CM limitation,loading too high?

Conduction Loss 2500V CM voltage limitation

Switching Loss May be OK – 6 kV CM voltage rating

2500V CM voltage limitation

Sen

sing

or

Dis

cret

e C

ompo

nent


2500V CM voltage limitation

Sensor Signal Best solution Loading, noise issues. May be loading issues2500V CM limitation

Discrete Components Best solution in all cases

May be loading issues2500V CM limitation

Sys

tem

Inpu

ts/O

utpu

ts


attenuation

Maximum 7600Vpk-pk

Expensive2500V CM limitation






high attenuation









June 21, 2017 16

Polling Question #2

What Applications/Signals do you Probe? (select one or more answers) Gate Drives Device Conduction Loss Device Switching Loss Floating Sensor Signals and/or Discrete Components Inverter Subsection Inputs/Outputs

June 21, 2017 17

Important Probe SpecificationsUnderstanding what each probe specification means is the first step in choosing the right probe for your application.

June 21, 2017 18

High Voltage Isolation The maximum common-mode voltage an attenuating probe can be safely used In power electronics, the DC Bus voltage = the maximum common-mode

voltage Signals floating on the DC bus need to be measured with an isolated probe

upper-side gate drive signal control or sensor signal

Common DC bus voltages 500 Vdc for 120/240Vac line inputs 1000 Vdc for 600Vac class line inputs 1500 Vdc for grid-tied solar PV inverters and UPS systems 6000 Vdc for 4160Vac inputs

Conventional high attenuation HV differential probes commonly have a UL (or other) safety rating This indicates the maximum common-mode voltage the probe can be used at to ensure

operator (for hand-held use), equipment and DUT safety

June 21, 2017 19

Common Mode Rejection Ratio (CMRR) Common Mode Rejection is the ability of the differential amplifier to ignore the

component that is common to both inputs. Real world differential amplifiers do not remove all of the common mode signal.

Additionally, differential probe leads/pairs must be perfectly matched for frequency response. This is hard to do with an attenuating probe lead set (but good results can still be obtained).

Common mode feedthrough sums with the VDM (signal of interest) into the output of the differential amplifier, becoming indistinguishable from the true signal.

The measure of how effective the differential amplifier + probe lead (pair) system is in removing common mode is Common Mode Rejection Ratio (CMRR). You will see CMRR expressed both in dB units or as a ratio of rejected voltage.

20log10(VSIGNAL/VMEASURED) = CMRRdB

Lower CMRR equates to greater noise and interference on the measured signal. High CMRR (100dB, or 100,000:1) at high frequencies is difficult to achieve with a

conventional high voltage (high-attenuation) probe topology.

June 21, 2017 20

Common Mode Rejection Ratio (CMRR)A simple test provides a reasonable measurement of your probe Connect the + and –

leads together at the measurement reference location e.g., the emitter or

source location of an upper-side device.

Acquire the signal View the interference

A measured transient during high dV/dt events indicates measured common-mode interference

C2 is HVFO High Voltage Fiber Optic Probe(Signal, GND and Shield leads connected at the emitter)

C1 is Upper-side Gate Drive (VG-E) Signal (acquired with HVFO)

M3 is HVD3106 HV Differential Probe(+ and – leads connected at the emitter)

~15V(5 V/div)

~1V(200 mV/div)

100 mV/div

June 21, 2017 21

Common Mode Rejection Ratio (CMRR)Comparing Field Measurement with Typical Factory-measured CMRR plot

Red line is 500x path (the attenuation used in the test at the left, required for this common-mode voltage)

Expected CMRR is ~32 dB at 9 MHz

Data above is taken in a controlled environment, parallel cables to minimize ground loops whereas test at the left is in “real-world” conditions.

Typical HVD3106 CMRR Performance

C1 (yellow) is HVFO measuring an upper-side gate-drive signal (VG-E)

M3 (blue) is an HVD3106 HV differential probe with the + and – leads connected together at the emitter (VE)

The measured 1V peak signal at the gate transition is the common-mode interference of the 15V signal. CMRR = 15:1 (24 dB) for this ~40ns rise time (BW = 0.35/TRISE = 9 MHz).

Note that the HVD3106 has the best CMRR of any probe in it’s class –but it can only be so good based on the topology of the design

No common-mode interference (HVFO), >100 dB CMRR

1V common-mode interference (HVD)

15V high dV/dt event (~10 MHz step response)

June 21, 2017 22

HVFO103 Product Overview

June 21, 2017 23

What is the HVFO103 High Voltage Fiber Optically-isolated Probe?Amplifier/Modulating TransmitterA frequency modulating optical transmitter is used for signal and data transmission across a fiber optic cable.

De-modulating ReceiverThe optical signal is received and de-modulated to an electrical output to the oscilloscope with correct voltage scaling.

Fiber Optic CableA standard 1m length cable is provided, but longer ones may be purchased for use.

Attenuating Tip AccessoriesAvailable in a variety of voltage ranges, e.g., +/-1V, +/-5V, +/-20V and +/-40V with a simplified pin socket termination

June 21, 2017 24

Key Characteristics

Compact, Simple, Affordable 60 MHz of Bandwidth (7.5ns rise time) 140 dB CMRR High Input Impedance (1 to 10 MΩ, depending on tip)

High impedance with low capacitance at low measured voltage = low DUT loading

Selectable Attenuation Tips for different voltage ranges ±40V to ±1V 1, 2 or 6 meter fiber optic cables available (lengths >25 meters available

direct from the cable manufacturer) 6 hour battery life ProBus compatible with newer Teledyne LeCroy oscilloscopes

June 21, 2017 25

What is Included with the HVFO103?

HVFO103 Includes:1. Qty. 1 Amplifier/Modulating

Transmitter2. Qty. 1 Demodulating Receiver3. Qty. 1 1m Fiber Optic Cable4. Qty. 1 USB Charging Cable5. Qty. 1 Micro-gripper Set6. Qty. 1 Soft Carrying Case

Attenuating Tips sold separately Each application/customer will

want something different

1

2

4

5

3

6

June 21, 2017 26

Attenuating Tip Accessories Four tips are available:

±1V (HVFO100-1X-TIP) – white ±5V (HVFO100-5X-TIP) – yellow ±20V (HVFO100-20X-TIP) – red ±40V (HVFO100-40X-TIP) – brown

The application will determine which tip(s) is required: Sensors: ±1V or ±5V MOSFET Gate Drives: ±5V or ±20V IGBT Gate Drives: ±20V or ±40V EMC Immunity Testing: Any

Match the attenuation of the tip to the voltage range of the measurement to minimize noise

June 21, 2017 27

Why Does the HVFO Have Three Leads? Blue wire is coaxial

Center conductor conducts signal current Return path for signal current is through

coaxial outer conductor Green wire is connected to measurement

reference and is also connected to outer coaxial signal conductor This ensures that ISIGNAL and IRETURN

currents are equal and opposite at the tip common-mode choke

Black wire also connects to the measurement reference And then is electrically connected to the tip

at the internal shield of the amplifier. The current flowing in this wire will drive

the reference voltage for the single-ended amplifier, accounting for any parasitic capacitance effects.

The three lead connection provides optimum CMRR at high frequencies.

June 21, 2017 28

Additional or Spare Fiber Optic Cables A 1m cable is included with the

HVFO103 Additional cables may be purchased

from Teledyne LeCroy HVFO-1M-FIBER HVFO-2M-FIBER HVFO-6M-FIBER

Cables may also be purchased direct from the supplier in these or any length We have tested to 25m, but longer

lengths will work as well http://www.i-fiberoptics.com/

1 meterHVFO-1M-FIBER

2 metersHVFO-2M-FIBER

6 metersHVFO-6M-FIBER

June 21, 2017 29

ComparisonConventional High Attenuation HV Differential Probe/Amp vs. HVFO103

DA1855A Diff Amp + DXC200A

DA1855A Diff Amp + DXC100A

HVD Series Differential Probe

HVFO103

Bandwidth 50 MHz 100 MHz 25-120 MHz 60 MHz

Attenuation 0.1 (gain) to 10x 1 to 100x 50-2000x 2-80x

Common-Mode Up to 155 VAppropriate for hand-held use

Up to 500VAppropriate for hand-held use

1, 2 or 6 kVAppropriate for hand-held use

35 kVNot for hand-held use – unit

must be appropriately separated from ground

Voltage Range 0.05 to 5V 0.5 to 500V 27.6 to 2000V ±1V to ±40V

Input Impedance 1 MΩ 1 MΩ 1 to 10 MΩ 1 to 10 MΩ

CMRR 100 dB 100 dB 80 dB 140 dB

Hand-held Rating 500V 500V 1, 2, or 6 kV 30Vrms/60Vdc

Price Most Expensive Most Expensive Least Expensive Mid-Range

June 21, 2017 30

Common Mode Rejection Ratio (CMRR)Comparison of a Conventional Differential Probe/Amp to a Fiber Optically-isolated Probe

Conventional HV Differential Probe or Amplifiere.g., Teledyne LeCroy DA1855A+DXC100A, HVD3106,

ADP305; Tektronix P5205, THDP0200

HV Fiber Optic Probee.g., Teledyne LeCroy HVFO103

A conventional high voltage differential probe topology requires that the probe measure small signal voltage + common-mode voltage across the lead capacitance = more probe loading on DUT, especially at high common-mode voltages.

The high voltage fiber optic probe only measures the small signal voltage since the probe amplifier is floating (battery-powered). This reduces the voltage across the lead capacitance = less probe loading at high common-mode voltages.

This probe pair must be precisely matched in impedance and frequency response to maintain CMRR – this is really hard to do!

A coaxial signal wire does not require matching for great CMRR.

Fiber optic isolation makes it easy to achieve great CMRR

June 21, 2017 31

Comparison of HVFO to a Conventional HV Differential Probes/AmpsCommon-mode Rejection Ratio (CMRR) for HVFO103 is far better than these other products

DA1855A (from Operator’s Manual) HVFO103

HVD3106 (from Operator’s Manual)

Specifications80dB @ 60 Hz65dB @ 1 MHz45dB @ 10 MHz30dB @ 100 MHz

Specifications100dB @ 100 kHz~85dB @ 1 MHz

50dB @ 10 MHz

Specifications140dB @ 100 Hz120dB @ 1 MHz

85dB @ 10 MHz60dB @ 60 MHz

June 21, 2017 32

Where is the HVFO103 needed and why?There are a lot of different probes used in power electronics testing. What niche is filled by the HVFO103?

June 21, 2017 33

HVFO is Superior For Two Key Applications Upper-side gate drive measurements

June 21, 2017 34

Sensor voltage measurements Floating, in-circuit EMI/RFI testing

Application Fit for High Voltage Fiber Optic (HVFO) ProbeThis highlights the application fit from our 170-1000 Vdc bus/link earlier in this presentation

170-1000Vdc Bus/Link


Single-endedActive


(VCM<VDCbus)

Active Single-ended

Rail-type(RP4030)



Series)

ActiveSingle-ended



(HVD Series)


Appl

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ion

/ Sig

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easu

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Pow

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Gate Drive Best solution in all cases

May perform acceptably – depends

on many variables

May perform acceptably – but very

expensive

Conduction Loss Best solution in all cases

Switching Loss Best solution in all cases

Sen

sing

or

Dis

cret

e C

ompo

nent

s Series/Shunt Resistor <1V can be noisy<1V can be noisy,

more CMRR interference


Sensor Signal Best solution in all cases

May be loading issues, could be noisy May be loading issues


Sys

tem

Inpu

ts/O

utpu

ts

Line Side (AC) Input Limited voltage range Best solution in all cases


required

DC Bus/Link Limited voltage range Best solution in all cases


required


Limited voltage range Best solution in all cases


required


Limited voltage range Limited voltage range, expensive



required


June 21, 2017 35

Comparison 1Comparing the Teledyne LeCroy HVFO103 to a low-cost HV differential probe for measurement of a SiC upper-side gate drive signal.

June 21, 2017 36

Teledyne LeCroy HVFO103 vs. “Generic, Low-cost” HV Diff ProbeBoth probes were in-circuit at the same time – this is not recommended! The customer is measuring an upper-side

gate drive signal floating at an unknown bus voltage (probably <500Vdc)

The customer had both probes connected in circuit at the same time This will not provide the best result for the

high performance probe The probe with higher loading (Elditest

GE8115) will add load to the circuit This added load will impact the

measurement made by the other probe (HVFO103)

You can see in the screen images that follow that the Elditest has some measurement impact on the HVFO103

If the Elditest GE8115 was not connected in circuit during the HVFO103 measurement, the HVFO103 would have performed even better.

Don’t connect both probes at the same time – the high attenuation HV diff probe will affect the HVFO103 result!

Teledyne LeCroy HVFO103 vs. Elditest GE8115 HV Differential ProbeThere is a large difference in performance between the two probes

HVFO103 with ±20V tip

Elditest GE8115 HV Differential

Probe

Zoomed area shown at right

100x Horizontal Zooms

Nice gate-drive shape. No

overshoot or preshoot. No

interference from other signals (great CMRR)

Measured gate-drive has

significant distortion due to poor CMRR and high circuit

loading Pickup from low-side high dV/dtswitching due to

poor CMRR

Excessive probe loading impacts

flatness of response

Excessive ringing likely due to high tip capacitance at high

voltage, poor CMRR, or both.

ElditestGE8115

HVFO103

High (100x) attenuation = high noise

Nice, constant amplitude, no overshoot or preshoot.

Highly variable response – likely

due to load changes in the

circuit

Teledyne LeCroy HVFO103 vs. Elditest GE8115This is a rise time comparison between the two probes


Time

Effi

cien

cyZoomed Area. In

fairness to the competitive probe, the zoom location is where

that probe performs best.

Note: Vertical Zoom was used to equalize amplitudes

and vertical positions. Horizontal position was

used to deskew the effects of different probe

propagation delays.

Zoomed area shown at right


ElditestGE8115

HVFO103


Probe

Teledyne LeCroy HVFO103 vs. Elditest GE8115 Signal rise time is ~17 ns, slew rate is ~1 V/ns. This is a (likely SiC) IGBT

Slew Rate and Rise Time are measured on the HVFO103 acquired signal. Rise time was measured with P1 Rise@level using 20-60% levels (due to ringing on

rising edge), then multiplied by 2 to make it comparable to 10-90% rise time value. Our HVFO103 Slew Rate specification is 3000 V/μs with 20x tip.

The device was described as an IGBT, and with this rise time,

it must be Silicon Carbide (SiC)

Excessive interference is likely

due to high tip capacitance at high

voltage, poor CMRR, or both.

ElditestGE8115

HVFO103~24V Gate Drive

signal, but from -8V to +15V, so +/-20V

tip was acceptable to use



Probe

Teledyne LeCroy HVFO103 vs. Elditest GE8115 5000x Zoom on Rise Time shows performance advantage


Same edge as previous slide, but this time with 5000x zoom

(10 times the zoom ratio as the previous slide).

ElditestGE8115

HVFO103

In this zoom, this interference seems

more to do with poor CMRR.

It appears that that Elditest GE8115 is loading down the

HVFO103.

This ringing is likely due to lead capacitance/inductance



Probe

Teledyne LeCroy HVFO103 vs. Elditest GE8115 Fall Time of ~10ns, Slew Rate of ~2 V/ns – about as fast as the HVFO103 can measure

Excessive ringing amplitude likely due to high tip capacitance at

high voltage, poor CMRR, or both.

The ringing measured with the HVFO103

may be in the signal, may be induced by

the Elditest probe, or some combination of these two - it is hard

to know. The customer had both

probes in the circuit at the same time, which

is not a good engineering practice.

Out of phase ringing is likely a result of poor

phase response of the Elditest probe

The falling edge Slew Rate is ~2V/ns (twice as fast as the rising edge) with Fall Time

~10ns. It is common for the falling edge to be faster.



Probe

Teledyne LeCroy HVFO103Measurement of the ring frequency indicates it is well within the HVFO bandwidth

The ringing occurs at a

frequency of ~35 MHz.

My belief is that the ringing is due to some

parasitic capacitance in their gate drive circuit, but it is hard to know for sure.

More than likely, the Elditest GE8115 probe

loading causes this slow return to ‘”0” signal level.

This is the previously measured “0” signal level.



Probe

Comparison 2Comparing the Teledyne LeCroy HVFO103 to a Teledyne LeCroy HVD3106 high voltage differential probe and a DA1855A differential amplifier with DXC100A HV probe pair for measurement of a Si upper-side gate drive signal.

June 21, 2017 44

Teledyne LeCroy HVFO103 Compared to HVD3106Upper-side Gate Drive Measurement

HVFO

HVD3106

M1 is HVFO M3 is HVD3106 HVD3106

performs much better than an inexpensive HV differential probe

June 21, 2017 45

Teledyne LeCroy HVFO103 Compared to DA1855A + DXC100AUpper-side Gate Drive Measurement

C2 is HVFO M1 is DA1855A DA1855A

performs similarly to the HVD3106

Notes: Circuit was a half bridge with a 465V DC Bus (common-mode). Signals were acquired in separate acquisitions, which is why pulse widths are slightly different. M1 Attenuation was incorrect by 10x

This higher negative voltage peak is due to worse CMRR of the DA1855A compared to the HVFO, and the DA1855A is known for excellent CMRR…

These voltage perturbations at board reference is due to CMRR and the loading of the DA1855A+DXC100A on the circuit.

This excessive amplitude is likely due to DA1855A circuit loading

This negative peak measured by the HVFO is real – it is due the thelower MOSFET high dV/dT during it’s switching

C2 is HVFOM1 is DA1855A

June 21, 2017 46

Upper-side Gate Drive MeasurementHVFO superior CMRR provides a better measurement

HVFO

Z1 is HVFO This acquisition

clearly shows the Miller effect plateau on the rising edge

HVFO accurately measures the Miller effect on the rising edge without interference from the lower-device switching (due to its great CMRR)

June 21, 2017 47

Comparison 3Comparing the Teledyne LeCroy HVFO103 to a Teledyne LeCroy ADP305 (older) and HVD3106 (newer) high voltage differential probe, and a DA1855A differential amplifier with DXC100A HV probe pair for measurement of an upper-side gate drive signal in an LED driver.

June 21, 2017 48

ADP305 alone in the circuit probing the gate drive signal

ADP305 in light blue (M3) alone in the circuit probing the signal

M3 is ADP305 HV Differential Probe

This transient, caused by the lower-side high dV/dt signal, is “artificial” and a result of the less than ideal CMRR of this probe. If “real” and present in the circuit and higher than the Miller plateau, it could cause a damaging shoot-through on the half-bridge.

Variation in what should be a DC level is caused by probe loading on the circuit and less than ideal probe CMRR.

Miller plateau

June 21, 2017 49

DA1855A with DXC100A probe pair alone in the circuit

DA1855A in yellow (C1) alone in the circuit probing the signal

Switching transients of lower side high dV/dt device are seen to impact the measurement

C1 is DA1855A + DXC100A Probe Pair

This transient, caused by the lower-side high dV/dt signal, is “artificial” and a result of the less than ideal CMRR of this probe. If “real” and present in the circuit and higher than the Miller plateu, it could cause a damaging shoot-through on the half-bridge.


Miller plateau

June 21, 2017 50

HVD3106 alone in the circuit probing the gate drive signal

HVD3106 in blue (C3) alone in the circuit probing the same signal

C3 is HVD3106 HV Differential Probe

This probe is showing a pretty reasonable response on this circuit. But the “artificial” transient is still pretty close in amplitude to the Miller plateau…

Miller plateau


June 21, 2017 51

HVFO103 alone in the circuit probing the same gate drive signal

HVFO in magenta (C2) alone in the circuit probing the signal

C2 is HVFO High Voltage Fiber Optic Probe

This transient is likely “real”, but is well below the Miller plateau, and a reasonable engineer would conclude that there is little cause for worry.

Miller plateau

Little to no variation in the DC level is due to reduced probe loading and excellent CMRR.

June 21, 2017 52

Comparison 4Comparing the Teledyne LeCroy HVFO103 to a Teledyne LeCroy HVD3106 high voltage differential probe for measurement of a floating sensor signal

June 21, 2017 53

Floating Sensor Signal MeasurementHVFO103 compared to HVD3106 measuring floating current sense resistor

M1 is HVFO C3 is HVD3106

Notes: Circuit was a single-device buck power conversion circuit with the power device and sense resistor on the high-side. ~500V DC Bus (common-mode). Signals were acquired in separate acquisitions to avoid having the HVD3106 load the circuit and impact the HVFO measurement.

Customer theorizes that higher probe loading of HVD3106 causes this improper response

Lower load capacitance of HVFO in circuit means that voltage response is more accurately measured.

Worse in-circuit CMRR of HVD3106 causes higher amplitude measurement in this area

M1 is HVFOC3 is HVD3106

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Comparison 5Comparing the Teledyne LeCroy HVFO103, HVD3106, and Passive Probe (for low voltage signal) to 1kV isolated inputs with input leads.

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Isolated Oscilloscope Inputs – Will They Work for Floating Signals?

Oscilloscopes with HV isolated inputs are safe to use, but will they perform well?

Not really The cables/probes used to

connect to the signal introduce a lot of L and C to the test circuit

The result is excessive ringing and poor signal fidelity

In general, isolated inputs are reasonably acceptable for: 50/60 Hz Line Voltage Inputs Low frequency PWM drive

output signals

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Upper-side Gate-drive Measurement ComparisonYokogawa DL850 Isolated Inputs Compared with Teledyne LeCroy

Yokogawa DL850 – 100 MS/s, 20 MHzIsolated input channels, high capacitance

long unshielded connections to DUT

Teledyne LeCroy HDO6104 with HVFO (yellow), passive probe (magenta) and

HVD3106 (blue)

Upper-side Gate-driveLower-side

Gate-drive

Phase Output Voltage

Upper-side Gate-drive

Lower-side Gate-drive

Phase Output Voltage

Large amounts of ringing

Poor CMRR or transient pickup from upper-side

HVFO measures signal perfectly

The Passive Probe shows limited interference from upper-side

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Polling Question #3

Have You Used an Oscilloscope With HV Isolated Inputs? Yes No Don’t Know

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Summary

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The HVFO103 High Voltage Fiber Optic Probe

Provides the capability to measure your signal as it truly is, in-circuit, without compromise

Is Simple, Compact, and Affordable Simple – a single laser and fiber optic cable for isolation and transmission.

Multiple tips achieve different operating voltage ranges Compact - small enough to fit into tight spaces. Affordable – fit the tightest of equipment budgets

Far surpasses the measurement capabilities and signal fidelity of both conventional HV differential probes and acquisition systems that rely on galvanic high voltage isolation

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View our On-Line Power Electronics Probing Webinar http://teledynelecroy.com

1. Choose Support2. Choose Tech Library3. Choose Webinars4. Select “Probing in Power

Electronics – What to Use and Why”

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http://teledynelecroy.com/

Available for Rental

www.trsrentelco.com / 844-879-0998

Questions?Contact Ken Johnson at [email protected]

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Webinar: High Voltage Fiber Optic (HVFO) Probe for Small Signal Floating Measurements

Engineering

Transcript of Webinar: High Voltage Fiber Optic (HVFO) Probe for Small Signal Floating Measurements