Under the heading FAQ (frequently asked questions), we provide answers to questions asked by our customers:

The driver circuits known under various designations, such as "two-stage turn-off", "soft switch-off", "slow turn-off" uses a low-ohmic gate resistor in normal operation to turn the IGBT off in order to minimise the switching losses, and a high-ohmic resistor (or lower gate current) whenever a short-circuit or over-current is detected. However the problem lies in the reliable detection of these conditions: VCE monitoring always involves a delay (known in this case as the response time) that must elapse before an error is detected. This time is as a rule up to 10us. If a short circuit is in fact present and the IGBTs are driven with a pulse which is shorter than the response time, the error is not detected and the circuit switches off too quickly. The IGBT is then destroyed via an over-voltage. Moreover the coverage of limit cases (between over-current / not over-current) poses a problem.

As a rule, such circuits must be regarded as dangerous and are therefore not used in CONCEPT products.

CONCEPT recommends mounted parts with minimum inductance values and worst-case dimensioning of the power parts, i.e. the gate resistance values should be selected so that over-currents and short circuits can be safely controlled at every turn-off and at maximum intermediate link voltages.

For high-power applications, CONCEPT has developed the SCALE plug-and-play driver series of drivers with an active clamping function. This represents a more complex but a better and more reliable solution than the "slow turn-off" approach already described.

The CE label refers to "complete" products that are sold to the end-user. In contrast, technical equipment is subject to the two machine directives, namely the low-voltage directive and the EMC directive. CE certification in the sense of the EC directive applies to machines, either individually or as a set, equipment that can be replaced (by the end-user!) and safety components sold individually. The EC directive defines a machine (quote) as "a totality of mutually connected parts or appliances of which at least one is movable, as well as of operating elements, control and energy loops etc., where applicable".

This definition clearly does not apply to IGBT drivers. Further, the directive lays down that "machines that do not operate autonomously" (supplier products, constituents of an end product, components) do not require any declaration of CE compliance. Voluntary marking of products (with the CE label) not liable to CE compliance is not permitted. IGBT drivers clearly belong to the class of "components" that can be incorporated into equipment and used only by a specialist.

For this reason, IGBT drivers are not liable to CE certification and are not permitted to carry a CE label.

The guideline refers to consumer products. It does not apply to capital goods, which include most power applications.

Most of the components used have already been lead-free for a longer period of time.

We have been using lead-free leadframes for many years, so there is no problem in using our drivers in a lead-free process.

Power modules are apparently also being converted only "superficially" to RoHS compliance, i.e. this applies only to their terminal pins or screws, but not their internal configuration (chips soldered on substrates and these on the baseplates).

In general, we have not noticed any great interest in RoHS-compliant products from our customers.