South-East European Industrial Market 2/2018
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INDUSTRIAL MARKET

6

SEE ELECTRONICS

SEE

NEWS

Microchip introduced new 8-bit

microcontroller families

Advancements in the architecture of PIC and

AVR 8-bit microcontrollers (MCUs) have optimized

the devices for implementing closed-loop control,

enabling systems to offload the Central Processing

Unit to manage more tasks and save power. To

help designers maximize performance and efficien-

cy in these systems, Microchip Technology Inc. has

introduced the new PIC18 Q10 and ATtiny1607 fam-

ilies, featuring multiple intelligent Core Independent

Peripherals (CIPs) that simplify development and

enable quick response time to system events.

Ideal for applications that use closed-loop con-

trol, a key advantage of using the PIC18 Q10 and

ATtiny1607 MCUs are the CIPs that independently

manage tasks and reduce the amount of process-

ing required from the CPU. System designers can

also save time and simplify design efforts with the

hardware-based CIPs, which significantly reduce

the amount of software required to write and vali-

date. Both families have features for functional safe-

ty and operate up to 5 V, increasing noise immunity

and providing compatibility with the majority of an-

alog output and digital sensors.

The slow discharging of the output capacitor can be

eliminated by using a load switch. For example, in Fig-

ure 2, the circuit used Q2 as a load switch andthe LED

dimming engine synchronously turns off the COG

PWM output and Q2 in order to cut the path of the

decaying current and allow the LED to turn off quickly.

Current Peaking

When using a switched-mode power converter for driv-

ing the LED, the feedback circuit is employed to regulate

the LED current. However, during dimming, the feed-

back circuit can create current peaking (see Figure 3)

when the operation is not handled properly. Looking back

at Figure 2, when the LED is on, a current is delivered to

the LED and the voltage across R

SENSE2

is fed to the EA.

When the LED turns off, no current is delivered to the

LED and R

SENSE2

voltage becomes zero. During this dim-

ming off-time, EA output increases to its maximum and

overcharges the EA compensation network. When the

modulated PWM turns on again, it takes several cycles

before it recovers while high-peak current is driven to the

LED. This current peaking scenario shortens the lifetime

of the LED.

To avoid this problem, the LED dimming engine al-

lows the PWM3 to be used as an override source of

the OPA. When the PWM3 is low, the output of the EA

is tristate which completely disconnects the compen-

sation network from the feedback loop and holds the

last point of the stable feedback as a charge stored in

the compensation capacitor. When the

PWM3 is high and the LED turns on again,

the compensator network reconnects and

the EA output voltage immediately jumps

to its previously stable state (before PWM3

is low) and restores the LED current set

value almost instantly.

Complete Solution

As mentioned earlier, a LED dimming en-

gine can operate with minimal to no CPU

intervention. Therefore, while offloading all

of the work for controlling the LED driver to

the CIPs, the CPU has significant band-

width to execute other important tasks.

Protection features, such as undervoltage

lockout (UVLO), overvoltage lockout (OVLO) and out-

put overvoltage protection (OOVP) can be executed by

processing the sensed input and output voltage. This

ensures that the LED driver is operating within desired

specifications and the LED is protected from abnormal

input and output conditions. The CPU can also pro-

cess the thermal data from a sensor to implement a

LED’s thermal management. Moreover, when setting

the dimming level of the LED driver, the CPU can pro-

cess triggers from a simple external switch or com-

mand from a serial communication. Also, the parame-

ters of LED driver can be sent to external devices

through the serial communication for monitoring or test-

ing.

Aside from the features mentioned above, the de-

signer has the luxury to add more intelligence on their

own LED application inclusive of communications, like

DALI or DMX, and control customizations. Figure 4

shows an example of a complete switched-mode dim-

mable LED driver solution using the LED dimming en-

gine.

Conclusion

A LED dimming engine can be used to create an ef-

fective switched-mode dimmable LED driver. The ef-

fectivity equates on its capabilities to drive multiple LED

strings, to provide efficient energy source, to ensure

LED’s optimal performance, to maintain a long life for

the LEDs and to add intelligence in the system.

Figure 3. LED dimming waveform

Figure 4. Switched-mode dimmable LED driver solution

Source: Microchip

LEM completed its range of

transducers dedicated to leakage

current measurement

LEM announced its range of low cost and light-

weight transducers dedicated to the measurement

of leakage current in PV inverters. The new LDSR

model is dedicated to measuring the leakage cur-

rent of 300 mA nominal up to 900 mA peak at 2

KHz frequency. The sensor is mounted onto a PCB

for primary and secondary connections & provides

an analogue voltage output.

“LDSR satisfies the needs of PV inverters, offer-

ing a competitive price, low dimensions and comply-

ing with all regulatory standards. LDSR is also an

excellent alternative to expensive fluxgate solutions

due to its small footprint and simple construction. As

well as ensuring safety in solar inverter installations,

LEM’s LDSR product is also ideal for a range of appli-

cations that include symmetry fault detection in me-

dium power inverters and failure detection in a range

of power sources,“ explains LEM.

The LDSR has been designed with an integrat-

ed primary conductor capable of 35 A on both the

phase and N line. The proprietary ASIC ensures

high-performance accuracy from -40 to +105°C ful-

filling the requirements of the EN 61209 standard,

added the company in an official statement.

Source: LEM