JPH098631A - LED drive circuit - Google Patents

Abstract

(57) [Summary] [Objective] To provide an LED drive circuit capable of preventing damage to an SI thyristor or a load, or preventing an SI thyristor from becoming unstable. [Structure] Light trigger / light quench LEDs 4a, 4b for light trigger / light quench for turning on and off an electrostatic induction thyristor, and power for driving the light trigger / light quench LEDs 4a, 4b In an LED drive circuit having a power supply V _CC , monitor means Q3b, Q4b for monitoring the current flowing through the light trigger / light quench LEDs 4a, 4b, and the monitor means Q3b, Q.
4b of monitoring results the optical trigger light quenching LED4a depending on the current corrected to undo the changes in current I _F flowing through 4b correction means Q3b, characterized in that it comprises a Q4b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention drives a light emitting diode (LED) to generate a trigger light and a quench light for turning on and off an optical trigger / quenching light electrostatic induction thyristor. The present invention relates to an LED drive circuit for.

[0002]

2. Description of the Related Art Conventionally, an optical trigger / optical quench optical static induction thyristor circuit having a circuit configuration shown in FIG. 2 is known. In the figure, the light trigger / light quench light static induction thyristor circuit is composed of a light trigger static induction thyristor (LTSI) thyristor Q1 and a static induction phototransistor (SIPT) Q2 of Darlington configuration, and the SIPTQ2 is mainly Static induction transistor (SI
T) Q21 and auxiliary static induction phototransistor (SIP
T) Q22. A speed-up resistor R _G is connected to the gate of the auxiliary SIPTQ22.

Further, the gate of the LTSI thyristor Q1 and the source of the main SITQ21 are interconnected, the cathode of the LTSI thyristor Q1 is directly connected, and the gate of the auxiliary SIPTQ22 is connected via a speed-up resistor R _G, and they are also interconnected. Main SITQ21 and auxiliary SI
The drain of PTQ22 is connected to the drain voltage V _D. The anode of the LTSI thyristor Q1 is connected as an output terminal to the power supply V _A via the load RL.

In the above structure, the main SI is in the normal state.
TQ21 and auxiliary SIPTQ22 are off and LT
SI thyristor Q1 is also turned off. In this state, when the gate of the LTSI thyristor Q1 is irradiated with pulsed trigger light (LT), the LTSI thyristor Q1 turns on, and a large current flows through the load RL through the LTSI thyristor Q1.

Also, the LTSI thyristor Q1 turns
When the gate of the auxiliary SIPTQ22 is irradiated with pulsed quench light (LQ) and the entire SI thyristor Q2 is driven in the ON state, the LTSI thyristor Q1
Gate voltage drops to V _D , and LTSI thyristor Q
1 turns off.

As described above, the LED driving circuit for generating the LT for turning on the LTSI thyristor Q1 and the LQ for turning off the LTSI thyristor Q1 is conventionally constructed as shown in FIG.

In the figure, the input terminal 1 is connected to LTSI.
An input signal having a frequency and a duty corresponding to the operating frequency of the turn-on and turn-off of the thyristor Q1 and the duty which is a ratio of the turn-on period and the turn-off period, respectively, is input. In this example, the input signal duty is 50% as shown in FIG.

The input signal input to the input terminal 1 is applied to the on-pulse generating circuit 2a and the off-pulse generating circuit 2b. In response to this, the on-pulse generating circuit 2a rises as shown in FIG. 4 (a). The ON pulse having a pulse width of, for example, 10 μs is applied to the gate of the MOSFET 3a at a timing corresponding to the above, and the OFF pulse generating circuit 2b outputs the timing corresponding to the falling edge of the input signal as shown in FIG. 4B. Then, an off pulse having a pulse width of, for example, 20 μs is generated and applied to the gate of the MOSFET 3b.

The MOSFET 3a has an LT LED 4a, which is a light emitting element for LT, and a current limiting resistor 5a.
The sources are connected to the + power supply V _CC via the, respectively, and the sources are connected to the ground, and when an on-pulse is applied to the gate, they are turned on to cause the LED 4a to emit light to generate LT. On the other hand, the MOSFET 3b has its drain connected to the + power supply V _CC through the LQ LED 4b, which is a light emitting element for LQ, and the current limiting resistor 5b, and its source connected to the ground, and turns on when an on-pulse is applied to its gate. Then L
The ED 4b is caused to emit light to generate LQ.

[0010]

However, in the above-mentioned LED drive circuit, the LED 4a for LT and the L 4 for LQ are used.
When the ED 4b deteriorates and their insulation increases, which increases the voltage drop in the LEDs 4a and 4b and reduces the flowing current, for example, as shown in FIG.
The current I _F flowing through the ED 4b decreases, the light output level of the LED 4b decreases, and the LTSI thyristor Q1 is turned on.
It may not be turned off, which may cause problems such as damage to the LTSI thyristor Q1 and the load. The same applies to the LED 4a. When the light output level of the LED 4a decreases due to deterioration, an unstable state may occur in which the LTSI thyristor Q1 cannot be turned on.

Therefore, in view of the above-mentioned conventional problems, the present invention prevents the SI thyristor from being turned off or turned off due to a decrease in the optical output level of the LED, and the SI thyristor and the load can be prevented. It is an object of the present invention to provide an LED drive circuit which can prevent damage to the LED or prevent the SI thyristor from becoming unstable.

[0012]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an optical trigger / optical quench optical trigger / optical quench LED for turning on / off an electrostatic induction thyristor and an optical trigger. In an LED drive circuit having a power supply for supplying power for driving the light quenching LED, monitor means for monitoring a current flowing through the light trigger / light quenching LED, and the light according to the monitor result of the monitor means The present invention is characterized by comprising a current correction unit that corrects an increase / decrease in the current flowing through the trigger / light quenching LED.

According to the present invention, the light trigger / light quench LED is connected so as to be forward biased between the power supply and the collector of the first transistor, and the monitor means and the current correction means are provided. Is composed of a second transistor Darlington-connected to the first transistor, the collector of the second transistor is connected to the power supply, and the emitter of the second transistor is connected to the base of the first transistor. I was supposed to.

Further, in the present invention, the light trigger / light quench LED is driven to emit light by an on-pulse and an off-pulse from the on-pulse generating means and the off-pulse generating means, respectively, and the on-pulse generating means and the off-pulse generating means are for supplying a constant voltage. It is assumed that the power source is connected in parallel to the power source via the shunt regulator.

[0015]

In the above structure, the monitor means is an optical trigger
When the increase / decrease in the current flowing through the light quenching LED is monitored, the current correction unit corrects the increase / decrease in the current flowing through the light triggering / light quenching LED so as to restore the change. Even if the light quench LED is deteriorated, the light output level of the light trigger / light quench LED is kept constant, and the SI thyristor is surely turned off or turned on.

Further, a second transistor is connected to the first transistor connected to the power supply between the second transistor and Darlington so that the light trigger / light quench LED is forward-biased so that the light trigger / light quench LED is forward biased. By configuring the monitor means and the current correction means by the second transistor so that the collector-emitter current of the second transistor becomes the base current of the first transistor, both means are simple and inexpensive. Can be realized.

Further, an on-pulse generating means and an off-pulse generating means for outputting an on-pulse and an off-pulse for driving light emission to the light trigger / light quenching LED, respectively, are connected in parallel to the power source via a shunt regulator for supplying a constant voltage. LE for optical trigger and optical quench
Even if the power supply voltage fluctuates due to the fluctuation of the voltage drop due to the deterioration of D, the voltage supplied to the on-pulse generation means and the off-pulse generation means is always kept constant by the shunt regulator, and the deterioration of the light trigger / light quench LED is on-pulse and off-pulse The light trigger / light quenching LED is indirectly actuated via the LED and the light output level thereof is prevented from fluctuating.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an LED drive circuit according to the present invention, in which the same parts as those of the conventional one described with reference to FIG. 3 are designated by the same reference numerals.

In FIG. 1, the input signal input to the input terminal 1 is applied to the on-pulse generating circuit 2a and the off-pulse generating circuit 2b. In response to this, the on-pulse generating circuit 2a changes as shown in FIG. An on-pulse having a pulse width of, for example, 10 μsec is generated at a timing corresponding to the rising edge of the input signal and applied to the base of the transistor Q3b, and the off-pulse generating circuit 2b outputs the input signal as shown in FIG. For example, 20 at the timing according to the fall
An off pulse having a pulse width of μ second is generated and applied to the base of the transistor Q4b.

The transistor Q3b is the transistor Q3a.
Darlington connection, the emitter of the transistor Q3b is connected to the base of the transistor Q3a, and the emitter of the transistor Q3a is connected to the ground. The collector of the transistor Q3b is directly connected to the collector of the transistor Q3a, which is the LT light emitting element LT.
+ Power supply V _CC (5 V in this embodiment) via the LED 4a for use
When an on-pulse is applied to the base of the transistor Q3b, both transistors Q3a,
Both Q3b are turned on to cause the LED 4a to emit light and generate LT.

Similarly, transistor Q4b is Darlington connected to transistor Q4a, the emitter of transistor Q4b is connected to the base of transistor Q4a, and the emitter of transistor Q4a is connected to ground. The collector of the transistor Q4b is directly connected to the collector of the transistor Q4a via the LED 4b for LQ, which is a light emitting element for LQ, and is connected to the + power supply V _{CC. When an} off pulse is applied to the base of the transistor Q4b, both transistors are connected. Both Q4a and Q4b are turned on to cause the LED 4b to emit light and generate LQ.

The on-pulse generation circuit 2a and the off-pulse generation circuit 2b are connected to the + power supply V _CC through the shunt regulator 6, and a predetermined secondary voltage (4.2 V in this embodiment) generated by the shunt regulator 6 is generated. ), An on-pulse and an off-pulse are supplied to the transistor Q4a,
Apply to the base of Q4b respectively. Although an ordinary three-terminal regulator can be used as the shunt regulator 6, in the present embodiment, a variable resistor is used to adjust the voltage value of the secondary side voltage supplied to the on-pulse generation circuit 2a and the off-pulse generation circuit 2b. The voltage value of the secondary side voltage is adjusted by connecting R and changing its resistance value.

As is apparent from the above description, in this embodiment, the transistors Q3a and Q4a correspond to the first transistor, and the transistors Q3b and Q4b are
It corresponds to the second transistor that constitutes the monitor means and the current correction means.

In the above structure, the LED 4a is turned on during the period of the on-pulse generated by the on-pulse generating circuit 2a in response to the rising edge of the input signal input to the input terminal 1, and the LED 4a is turned on.
Issue T. At this time, due to deterioration of the LED 4a, this LE
When the current I _F1 flowing through D4a decreases and the optical output level of the LT starts to decrease, the transistor Q3 correspondingly decreases.
b collector of - emitter current I _C1 increases the base current of the transistor Q3a is increased, the collector of the transistor Q3a - conductivity of the emitter is larger LED4a
Current I _F1 flowing to the LED is increased and the LT emitted from the LED 4a
Is returned to the original light output level and is kept constant.

The same is done for the LQ emitted by the LED 4b, so that the turn-on and turn-on of the SI thyristor are reduced due to the decrease of the optical output level of LT and LQ.
It is prevented from being turned off, for example, the SI thyristor cannot be turned off until it is turned on.

Further, due to deterioration or the like, the LED 4a and the LED
Even if the voltage drop at 4b increases and the power supply voltage of the + power supply V _CC fluctuates, the secondary voltage received by the on-pulse generation circuit 2a and the off-pulse generation circuit 2b from the shunt regulator 6 is the resistance value of the variable resistor R. It is kept constant depending on the setting of,
Q is kept at a constant light output level, thus LT and L
The turn-on and turn-off of the SI thyristor are not performed due to the decrease in the optical output level of Q.
It is more surely prevented that the SI thyristor cannot be turned off until it is turned on.

In this embodiment, the transistor Q in which the LED 4a and the LED 4b are provided between the + power source V _CC and the transistor Q
LED4 by transistor Q3b and transistor Q4b which are Darlington connected to 3a and transistor Q4a.
Since the means for holding the light output level of the LED a or the LED 4b constant is configured, this means can be realized easily and at low cost.

[0028]

As described above, according to the present invention, a light trigger / light quench LE for turning on and off a light trigger / light quench light electrostatic induction thyristor.
In an LED drive circuit having D and a power supply for supplying power for driving the light trigger / light quench LED, monitor means for monitoring a current flowing through the light trigger / light quench LED, and monitor of the monitor means According to the result, a current correction unit is provided to correct the increase / decrease in the current flowing through the light trigger / light quench LED. Therefore, even if the light trigger / light quench LED is deteriorated, the light output level of the light trigger / light quench LED is kept constant, and the light trigger / light quench light electrostatic induction thyristor is reliably turned off. Or, the photoelectrostatic induction thyristor is turned on, so that the photoelectrostatic induction thyristor cannot be turned off, and the photoelectrostatic induction thyristor itself or the load is damaged. It is possible to prevent the photo static induction thyristor from becoming unstable due to the inability to turn on.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an LED drive circuit according to the present invention.

FIG. 2 is a circuit diagram showing an example of the configuration of a general static induction thyristor circuit.

FIG. 3 is a circuit diagram of a conventional LED drive circuit.

FIG. 4 is a waveform diagram showing a state of each part in the circuit of FIG.

[Explanation of symbols]

2a On-pulse generation circuit (on-pulse generation means) 2b Off-pulse generation circuit (off-pulse generation means) 4a Light trigger LED 4b Light quench LED 6 Shunt regulator I _F1 current Q3a, Q4a Transistor (first transistor) Q3b, Q4b Transistor (first) 2 transistor, monitoring means, current correction means) V _CC + power supply (power supply)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H03K 17/725 9184-5K H03K 17/60 B

Claims (3)

[Claims] 1. An optical trigger, an optical quench, an optical trigger for turning on and off an electrostatic induction thyristor.
Light quench LED and light trigger / light quench LE
In an LED drive circuit having a power supply for supplying driving power of D, a monitor means for monitoring a current flowing through the light trigger / light quench LED, and the light trigger / light quench according to a monitor result of the monitor means. An LED drive circuit comprising: a current correction unit that corrects an increase / decrease in current flowing through the LED for use. 2. The light trigger / light quenching LED comprises:
The second bias transistor is connected between the power source and the collector of the first transistor so as to be forward-biased, and the monitor means and the current correction means are second transistors in Darlington connection with respect to the first transistor. The LED drive circuit according to claim 1, wherein the LED drive circuit is configured so that the collector of the second transistor is connected to the power supply and the emitter thereof is connected to the base of the first transistor. 3. The light trigger / light quenching LED comprises:
3. The light emission is driven by on-pulses and off-pulses from the on-pulse generation means and the off-pulse generation means, respectively, and the on-pulse generation means and the off-pulse generation means are connected in parallel to the power source via a shunt regulator for supplying a constant voltage. The described LED drive circuit.