CT11 Series

High Isolation Current Sense Transformers

The CT11 Series combines high isolation with reliable measurement of moderate primary currents in power electronic systems. Supporting up to 30 A primary current with turns ratios from 1:50 to 1:200, it provides flexible signal scaling for control and protection circuits. The series features a compact surface-mount footprint of approximately 13.5 mm × 13.0 mm with a 14.4 mm maximum height, enabling reliable PCB integration.

The CT11 Series features an ET product up to 1627 V-µs and 3000 VAC isolation strength, enabling dependable current sensing across high-voltage boundaries. Designed for an operating temperature range of –40 °C to +130 °C, the series supports demanding industrial and embedded environments. It is engineered to comply with updated insulation requirements in accordance with IEC 61558-1 and IEC 62368-1, making it well suited for DC/DC and AC/DC converters, feedback and control systems, point-of-load regulation, and power-fault monitoring circuits.

Key Features

Surface-mount package for direct PCB integration
Compact 13.5 mm × 13.0 mm footprint, 14.4 mm max height
Supports primary currents up to 30 A
Supports switching frequencies up to ~1.0 MHz ¹¹
Multiple turns-ratio options from 1:50 to 1:200
3000 VAC primary-to-secondary isolation (Hi-Pot tested)
Suitable for switching-power and line-frequency current sensing
UL 94V-0 flammability rated materials for safety compliance
Designed to comply with updated IEC insulation requirements

APPLICATIONS

DC/DC converters requiring isolated current measurement
AC/DC power supplies with feedback and protection monitoring
Current-sense feedback for regulation and control systems
Point-of-load (POL) converters and distributed power architectures
Over-current, load-drop, and fault-detection circuits
Industrial and embedded power systems requiring galvanic isolation

Electrical Specifications @ 25°C - Operating Temperature Range^1-2: -40°C to +130°C

Part Number

Turns Ratio
(TR)

Secondary Inductance ³
(mH, Min)

Secondary DCR
(Ω, Max)

Current Rating ⁴
(RMS) (A, Max)

ET Product ⁹
(V-μs, Max)

Terminating Resistance ⁷
(Ω, Ref)

Accuracy Range ¹²
(kHz, Ref)

SRF ⁶ (3-4)
(kHz, Typ)

CT11-050

1:50

2.0

0.4

407

0.8

3 — 300

1008

View

CT11-070

1:70

3.9

0.9

569

1.2

2 — 250

752

View

CT11-100

1:100

8.0

1.5

813

1.7

1.5 — 150

511

View

CT11-125

1:125

12.5

2.4

1017

2.1

1.25 — 125

424

View

CT11-200

1:200

32.0

6.2

1627

3.3

1 — 80

254

View

Part Number

Terminating Resistance ⁷
(Ω, Ref)

CT11-050

0.8

View

CT11-070

1.2

View

CT11-100

1.7

View

CT11-125

2.1

View

CT11-200

3.3

View

Mechanical Drawing

Footprint

Schematic

1.
Operating Temperature Range: The combination of ambient temperature and temperature rise.
2.
Storage Temperature Range: Applies to parts removed from original packaging.
3.
Secondary Inductance: Tested at 10kHz, 1V_RMS.
4.
Current Rating: Peak current (50% duty cycle) through primary (1-2) to cause 40°C temperature rise at 25°C ambient.
5.
Primary DCR (1-2): 0.500 mΩ (Ref)
6.
SRF: Values are for reference only.
7.
Terminating Resistor (R_B): Based on 0.5 V output voltage with 30 A current flowing through the primary. Varying terminating resistance increases or decreases output Voltage/Ampere.
8.
Flammability Standard: Meets UL 94V-0.
9.
ET Product: The maximum ET is based upon a flux density of 3700 Gauss at 25°C. Suitable for bipolar applications only.

ET = E_O/2f
E_O = I_PR_B/TR

Where as,

E_O = Output voltage (V) TR = Turns Ratio
R_B = Term. Resistor (Ω) f = Frequency (Hz)
I_P = Primary Current (A)
10.
Hi-Pot Rating: Tested @ 60Hz, 1mA, 1 min.
11.
Usable Frequency Range: Effective detection bandwidth, extending beyond the SRF when appropriately burdened.
12.
Accuracy Range: Optimized for precision current detection within the defined usable bandwidth, from (Min. Frequency x 5) to (30% SRF). Contact ICE for specific questions about frequency ranges.
13.
PACKAGING
- Reel Diameter: 330 mm
- Reel Width: 32 mm
- Pieces/Reel: 150
- Reel/Carton: 8
- Pieces/Carton: 1200
14.
Compliance & Solutions:
15.
Specifications subject to change without prior notice.

Frequently Asked Questions (FAQs)

How is the output voltage of a current sense transformer determined?

The output voltage depends on the primary current, turns ratio, and terminating (burden) resistor. Increasing the burden resistor increases the output voltage per ampere of primary current.

Why is a terminating resistor required on the secondary winding?

A terminating resistor converts the sensed secondary current into a measurable voltage signal and stabilizes the transformer’s frequency response.

How does the ET product affect current sensing performance?

The ET product defines the maximum volt-second capability before core saturation occurs. Operating within the specified ET limit ensures accurate waveform reproduction.

What happens if the transformer core saturates during operation?

Core saturation causes distortion of the sensed waveform and reduces measurement accuracy, potentially affecting feedback or protection circuits.

What determines the accuracy bandwidth of the CT11?

The usable accuracy range is typically defined between five times the minimum frequency and approximately 30% of the self-resonant frequency (SRF) when properly terminated.

What role does the self-resonant frequency (SRF) play in performance?

SRF represents the point where parasitic capacitance cancels the inductive behavior of the transformer. Operation well below SRF ensures stable sensing performance.

How does the turns ratio affect measurement sensitivity?

Higher turns ratios produce a larger secondary signal for a given primary current, allowing designers to tailor signal levels for ADCs or control circuitry.

Can current sense transformers detect very low currents accurately?

Accuracy at low current levels depends on the selected turns ratio and burden resistor, which together determine the signal amplitude relative to noise.

Why are current sense transformers commonly used instead of shunt resistors in high-power systems?

They provide galvanic isolation, lower insertion loss, and reduced power dissipation, making them well suited for high-current and high-voltage environments

How does the burden resistor value influence measurement range and sensitivity?

The burden resistor determines the voltage generated from the secondary current. A higher resistor value increases output sensitivity but may reduce bandwidth, while a lower value improves bandwidth and dynamic response.