IRPLLED1A International Rectifier, IRPLLED1A Datasheet - Page 22

• Manufacturer Part Number: IRPLLED1A
• Description: Power Management IC Development Tools Hi-Vlt DC-DC Buck Cnvr HBLED Cur Cntrl
• Manufacturer: International Rectifier
• Type: DC/DC Converters, Regulators & Controllersr

Specifications of IRPLLED1A

• Product: Power Management Development Tools
• Tool Is For Evaluation Of: IRS25401PBF
• Output Voltage: 16 V to 24 V
• Output Current: 350 mA to 1.5 A
• Factory Pack Quantity: 1

9. Open circuit protection
Fig. 29 IRPLLED1A Improved Open Circuit Protection Scheme
The overvoltage / open-circuit protection circuit shown in Figure 29 replaces schemes used on previous versions of
the IRPLLED1A reference design. This method offers far more reliable performance.
The output over voltage / open circuit protection circuit shown in Figure 29 allows the designer to program the
allowable maximum output voltage by means of ROV1 and ROV2. An industry standard programmable zener diode
type LM431 (IC2) is used to pull down the base of Q1, which pulls down on VCC when the divided voltage from
ROV1 and ROV2 exceeds the internal 2.5V reference. IC2 is capable of sinking no more than 100mA and in the
SOT-23 package has limited power handling ability, therefore Q1 was added to pull down the VCC voltage fed from
RS1 and RS2 to below the under voltage lockout threshold VCCUV- of the IRS25401/11 causing it to shutdown.
This circuit reacts very rapidly when the output voltage exceeds the predetermined level. It operates whether or not
an output capacitor is connected, i.e. in any of the alternative JDIM jumper positions.
The over voltage protection threshold has been set to 32V in the IRPLLED1A Rev D demo board to allow one or
two standard LED panels to be connected in series to the output before reaching a voltage level high enough to
trigger the protection circuit. The open circuit protection circuit operates in hiccup mode such that Q1 pulls the
VCC voltage below the VCCUV- threshold causing the IRS25401/11 to switch off and enter micro power mode and
the output to fall to zero. VCC then charges up again through RS1 until the voltage again exceeds VCCUV+ and the
IRS25401/11 starts up again. The sequence then repeats until a load is added to clamp the output voltage.
The above circuit is able to limit the output voltage to a series of pulses instead of a DC level. However it should be
noted reducing the average output voltage does not prevent the possibility of electric shock in non-isolated
systems! Therefore an IRS25401/11 based Buck LED driver running directly off line would still be an electric shock
hazard and it would not be safe to attempt to replace the LEDs if such a system were powered. In non-isolated
systems, additional mechanical protection is required to ensure that access to the LEDs is not possible or alternative
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