JPS5919382A - Heat response compensating system for light emitting diode - Google Patents

Abstract

PURPOSE:To prevent the deterioration due to variation in the temperature by varying the diode drive current by the junction temperature detected by the forward voltage of a light emitting diode. CONSTITUTION:A light emitting diode (LED) 4 is driven by a gain variable amplifier 1, and LED drive circuits 2, 3, and jigs junction temperature is detected by a junction temperature detector 5. The detector 5 has a resistor Ri, connected in series with the LED 4, a resistor R, a diode D, and an operational amplifier 6, and the junction temperature is detected by the forward voltage of the LED 4. The detected temperature signal is fed through a voltage control operational amplifier 7 to a gain variable amplifier 1, thereby controlling the drive current of the LED 4. Thus, the nonlinearity between the light emitting power and current of the LED 4 can be improved and the deterioration of the characteristics can be prevented.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a direct light intensity modulation method using light emitting diodes (LEDs), in which currents caused by changes in the junction temperature of the light emitting diodes due to current changes that degrade characteristics.
The present invention relates to a method for improving nonlinearity between emission powers.

6) Prior art and problems In the conventional technology, methods for improving the non-linearity between the current and the light emitting power due to the above-mentioned junction temperature change include compression of the amount of change using emphasis and tie-emphasis circuits;
Alternatively, general improvement methods such as the feed-forward method and the pre-distortion method are used, and an optical analog link that is sufficiently practical for purposes such as TV is provided.

However, higher quality broadcasting applications require stricter waveform characteristics, and the prior art has the disadvantage that waveform deterioration due to junction temperature changes cannot be ignored.

(e) Object of the invention The object of the present invention is to eliminate the above-mentioned drawbacks [7] and to provide a good method for compensating for changes in the luminous power of light-emitting diodes due to thermal cropping.

(d) According to the present invention, the object described in the configuration of the invention is to include a detection section that detects the solar temperature of a light emitting diode according to the forward voltage of the light emitting diode, and a detection section that detects the temperature of the light emitting diode according to the forward voltage of the light emitting diode. This is achieved by providing a thermal response compensation method for a light emitting diode, which is characterized by comprising a gain variable section that changes a drive current.

(e) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

The figure shows a configuration example of the present invention. In the figure, 1 is a variable gain amplifier, 2 and 3 are LED drive circuits, 4 is a light emitting diode, and 5 is a junction temperature detection circuit, which includes an operational amplifier 6. 7 indicates an operational amplifier for voltage amplification. Furthermore, R1
is an external resistance having the same value as the internal resistance of the light emitting diode 4, D is a rectifier having voltage-current characteristics similar to that of the light emitting diode, and R is a resistor having the same value as the internal resistance of D.

Generally, in an LED, the light emitting power is inversely proportional to the junction temperature, so the present invention detects the junction temperature and uses this to compensate for changes in the light emitting power. In other words, the junction temperature of the light emitting diode is detected by the change in the forward voltage of the light emitting diode (junction temperature and forward voltage are proportional). This is offset by a circuit consisting of a diode and a resistor that does not cause any change, and only the forward voltage change due to temperature is extracted, and the LED drive current is adjusted by the forward voltage change to change the light emitting power. This will compensate for the amount.

The forward voltage of the LED is VF, its temperature change is ΔvF, the current flowing through the LED is I, and the current flowing through D is l.
Then, vl-R1・■10VF+ΔVF
(1) V2=R・1+VF
(2) The voltage at point A is V. Then, vo = V, 10R1-I = 2R1・■10VF1ΔVF
(3) On the other hand, V, -V F= 2 R・1, 1 ・°bow −100 (Vo−VF) (2) Yoshi V, = R・2R− (VoVF) 10V1r−2 (Vo
VF) 1 Vp (3) is 1 Vt 2 (2Ri・I +VF1ΔVF−vF
) +v1= (4)v2-R1・■ten(TΔVp・+
VF) (5) = 3- If the difference between Vl and V is Vs, then v, = - ΔvF 2 (6) where v3 represents the amount of voltage change due to temperature change. If the change in LED light emitting power is ΔP, then ΔP is inversely proportional to ΔT. If the change in Junxillon temperature is ΔT, ΔT is ΔT.
Proportional to vF.

In this way, changes in light emitting power due to thermal changes in the light emitting diode can be compensated for.

Generally, the value can be changed by ΔVF/ΔT-2 to 4 mV/°C ΔP/ΔT=0.05 factor/°C. Therefore, it is possible to compensate for a change in light emission power due to a change in junction temperature that changes with a change in the signal current itself.

(f) Effects of the Invention As explained in detail above, the present invention has the great effect of improving the nonlinearity of the luminous power flow rate of the light emitting diode.

[Brief explanation of drawings]

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Claims (1)

[Claims] It is characterized by being comprised of a detection section that detects the junction temperature of the light emitting diode based on the forward voltage of the light emitting diode, and a gain variable section that changes the driving current of the light emitting diode based on the output of the detection section. Light emitting diode thermal response compensation method 0