Avago Tech Note: 14.2mm wide Creepage and clearance optocouplers for high-voltage applications
The ACNT family of wide optocouplers offers 14.2mm creepage and clearance for high voltage applications. These optocouplers are able to achieve 2,262 VPEAK insulation working voltage in a stretched compact SO-8 package. To address the needs for a comprehensive isolation solution in high voltage and noisy environment, the ACNT family consists of three products: the ACNT-H313, a high efficiency gate drive optocoupler for driving IGBTs; the ACNT-H61L, a low power 10MBd digital optocoupler for system control and data communications isolation; and the ACNT-H790, a high linearity isolation amplifier for current and voltage sensing applications.
Creepage and Clearance Requirements
Today high-voltage power systems require chip-level components to support well insulated and noise-immune large signals to minimize copper wiring costs while maintaining optimal power efficiency. In the drives systems, the benefits of using 690 VAC line voltage are power efficiency with power increases without current increases and lesser copper losses. This saves overall system costs in term of cable size, transformer size and installation cost.
According to the adjustable speed electrical power drive system safety IEC 61800-5-1 (ref IEC 60664-1), to determine the creepage requirements for a working voltage of the drive, design engineers need to consider several factors such as insulation type (basic or reinforced), pollution degree, and insulation material group. The factors of impulse voltage, working voltage and altitudes dictate multiplication factor and requirement for clearance.
Table 1 shows various market segments with the required creepage and clearance distance needed for pre-determined bus and working voltages. For example, a working voltage 630 VAC drive system with DC bus voltage 1200 V, pollution degree 2 and insulation material group III, requires 12.6mm minimum creepage for reinforced insulation.
Table 1. Market segments with wide creepage and clearance trend
Revision in the regulatory standards can call for wider optocouplers need. For example, from 2016, the harmonization of international standard bodies UL and IEC transits UL 508C to IEC 61800-5-1 will mean more stringent creepage and clearance requirements for new drive model while maintaining the same rating specifications. The ACNT family suits well to meet this revision and implementation.
It is Not Just About Creepage and Clearance
In other market segments, high insulation voltage or transient overvoltage capabilities is more critical in choosing a good isolation solution. An example is the medical devices - The new 4th edition medical standard IEC 60601-1-2 calls for higher levels 8 kV contact and 15 kV air between the sensing circuitry with direct patient or user contact to the control MCU board of patient monitoring device (Figure 1). Avago 14.2mm optocouplers with an internal clearance of 0.5mm, high transient overvoltage of 12 kV and its compact package meet this. The stretched wide package also improves the isolation gap and protection against electric arc discharge.
Figure 1: ACNT-H61L in patient monitoring device
The Avago ACNT family provides a complete isolation solution of a motor control system as shown in Figure 2. To isolate the low voltage “brain” or MCU and the high voltage power electronics, the ACNT-H313 2.5A gate driver suits driving power IGBTs and MOSFETs with excellent common- mode rejection noise performance of 40 kV/µs at 2000 VCM. For the isolated motor phase current and voltage measurements, the ACNT-H790 isolation amplifier offers ±3% gain tolerance with excellent linearity and dynamic performance of 60 dB SNR. Its specifications of 200 kHz bandwidth and 1.6 µs fast response time allow capture transients in short circuit and overload conditions.
For data bus communication isolation or simply provide isolation between low voltage control and high voltage power (eg. HVIC or IPM), the ACNT-H61L digital 10 MBd optocoupler offers the lowest power consumption (less than 20mW) 14.2mm optocouplers available in the market.
Figure 2: A complete isolation solution in the motor control system