Industry news

2016August

High power white LED high symmetrical flow parallel power supply system (a)

From: www.szbako.com Data:07/08/2016

Abstract: in order to solve the problem of visible light communication system's white LED (light emitting devices) light source with high stability of DC bias power supply, the design and development of the a buck DC /DC Direst Cunent parallel supply system. The system adopts ARM7 (lpc2148) as the main controller, using voltage feedback to adjust the two DC /DC module of PWM (pulse width modulation) drive signal of duty than to achieve voltage regulation, using two PMOS (P-channELMetal-Oxide-Semiconductor) electronic switches respectively control two DC /DC branches to achieve current sharing. Experimental results show that the actual output voltage of the power source and the set value of the error is less than 2%, less than 1% to the deviation of the two branch current, power supply efficiency is up to 75% ~ 80%. In the power opening and off moment instantaneous test results show, driving voltage spike phenomenon, voltage from 0 rose to 1. 6 V time is about 20 s, electric fell to 0 time is about 65 S. two DC /DC modules work alternately, prolongs the service life of the power supply system. The power supply system in the lighting LED and visible light communication equipment has a good application prospect, for the design of DC /DC module with high symmetrical flow parallel power supply system to provide a solution.

0 Introduction modular design of

2 system. DC /DC Buck type voltage stabilizing circuit PMOS tube type SI4405, PMOS drive for ADP3624; pwm1, pwm2 grounds ARM7 frequency fixed, occupies emptiescompared adjustable square wave signal, respectively, the regulation of the output voltage of the DC /DC branch. In order to obtain a stable output voltage, take the following design scheme:

1) the reasonable choice of PWM frequency, effectively reduce the output voltage ripple coefficient, the design takes 20 kHz.

2) when the load changes, through the difference size calculated output voltage (by the AD sampling) and the target value by fuzzy PID (Proportion-Integral-Derivative) algorithm, pwm1 regulation, pwm2 accounted for air ratio, in a relatively short period of time, stable adjustment of the output voltage to the desired value.

two DC /DC branch current sharing scheme are as follows: at the output end of the two DC /DC circuit are respectively connected with a high-speed PMOS electronic switch, by using ARM7 output a 50% duty ratio of square wave signals pwm3 a PMOS electronic switch control. At the same time, the Party of the wave signal inverting signal control another branch of PMOS electronic switch. The two branch output voltage is equal, and the 50% time in push-pull mode, which can realize the uniform flow effect.

2 current and voltage acquisition module

2.3 over current protection and self recovery module

the parallel current sharing power supply system with over current protection and self recovery function, the realization of the principle as shown in figure 3. Its working process is as follows. 1) the voltage signal which is output by the Holzer current sensor is amplified and compared with the voltage, which is used to drive the relay. 2) if the current exceeds such capacity, the comparator outputs high level, at this time relay drive 2 immediately action. At the same time, the DC /DC main circuit of K1 and load circuit K2 disconnected (avoid DC /DC storage capacitor to charge to the load), the formation of double overcurrent protection. 3) due to the DC /DC main circuit and the load circuit to turn off the rear when, Hall current sensor output voltage can't make the comparator to output high voltage, so the relay drive 2 cannot make K1 and K2 to disconnect. The damage for longer without the protection of electronic circuit design, adding delay protection circuit, when the voltage comparator outputs high level (2 relay driver has been working), to charge a storage capacitor (due to the charging time constant, the charging process is very short). When the relay driver 2 to stop working when the by charging the capacitor discharge will cause the relay driver 1 in a long time to action, so as to maintain K1 and K2 continued to disconnect, the formation of delay protection (K1 and K2 by 1 and 2 dual control relay drivers, any one of the work, can make the two break) when the relay driver 1 or.4) 2, can lighten LED, send the alarm signal.

5) when the relay drive 1 and 2 do not work, relay switch K1 and K2 pull, led warning lamp to achieve self recovery.

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