TWM461959U - DC-to-DC constant current driving circuit - Google Patents

Description

DC to DC constant current drive circuit

The present invention relates to the field of circuits, and more particularly to a DC-to-DC constant current driving circuit.

In the field of DC to DC switching power supply and lighting, DC to DC constant current drive circuit is widely used. For example, the current common Light-Emitting Diode (LED) is driven by a DC-to-DC constant current driving circuit. In the field of display backlights, whether the display screen uses multiple strings of LEDs or a single string of LEDs as the backlight source, it is necessary to use a DC-to-DC constant current driving circuit to drive the LEDs included in the display.

In order to achieve constant current control, output current pulse width control, and abnormal state fail-safe function for load circuits such as LED light strings, the present invention provides a novel DC-to-DC constant current drive circuit. .

The DC-to-DC constant current driving circuit according to the embodiment of the present invention includes a DC-to-DC switching circuit, an output overvoltage protection circuit, a constant current sampling control circuit, an output current pulse width adjustment circuit, and a system enable terminal control circuit, wherein the DC The DC switching circuit includes a wafer control circuit. The pulse width modulation control chip in the chip control circuit comprises: a system loop compensation leg, grounded via a system loop compensation capacitor and a system loop compensation resistor; a wafer enable control signal input pin connected to the system enable terminal control line; The optical signal input pin is connected to the output current pulse width adjusting circuit; the metal oxide semiconductor field effect transistor driving pin is connected with the metal oxide semiconductor field effect transistor included in the DC to DC switching circuit; the grounding pin and the chip reference ground The peak current sampling input pin is grounded via a sampling resistor; the output current setting pin is connected to the constant current sampling control line and the output overvoltage protection line; and the internal circuit power supply pin of the chip, the input voltage is filtered by the filter capacitor and connected to the internal circuit of the chip Power supply foot.

The DC-to-DC constant current driving circuit according to the embodiment of the present invention can implement constant current control, output current pulse width control, and fail-safe function of an abnormal state to the load circuit.

1‧‧‧DC to DC switch circuit

2‧‧‧Output overvoltage protection circuit

3‧‧‧Constant current sampling control circuit

4‧‧‧Output current pulse width adjustment circuit

5‧‧‧System enable control line

C1‧‧‧ input filter capacitor

C2‧‧‧Output voltage filter capacitor

D1‧‧‧Boost diode

L1‧‧‧Boost Inductance

1-1‧‧‧ wafer control circuit

Q1‧‧‧Metal Oxide Semiconductor Field Effect Transistor

Z1‧‧‧ Voltage Regulator

Fuse‧‧‧Fuse

C _CMP ‧‧‧ system loop compensation capacitor

R _CMP ‧‧‧ system loop compensation resistor

R _CS1 , R _CS2 ‧‧‧Sampling resistor

C _VIN ‧‧‧Filter Capacitor

R _OVP1 , R _{OVP2 ‧‧‧voltage} resistor

R _FB , R _FB1 , R _DIM , R _ENA ‧ ‧ resistance

1 shows a circuit diagram of a DC-to-DC constant current driving circuit according to an embodiment of the present invention (wherein a load circuit is exemplarily shown as an LED light string).

Fig. 2A and Fig. 2B show two connection modes of the LED light string shown in Fig. 1.

Features and exemplary embodiments of various aspects of the present work are described in detail below. The following description covers many specific details to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely provided to provide a clearer understanding of the present invention by the example of the present invention. The present invention is in no way limited to any specific configuration as set forth below, but without departing from the spirit of the present invention, any modification, substitution, or modification of the related elements or components.

Fig. 1 is a circuit diagram showing a DC-to-DC constant current driving circuit according to an embodiment of the present invention. It should be noted that the DC-to-DC constant current driving circuit according to the embodiment of the present invention can be widely applied to various switching power supply applications.

However, for convenience of description, FIG. 1 illustrates a DC-to-DC constant current driving circuit according to an embodiment of the present invention by taking an example of application to an LED light string. Of course, those skilled in the art should understand that the DC-to-DC constant current driving circuit of the present invention is not limited to the application of the LED constant current driving application.

As shown in FIG. 1, the DC-to-DC constant current driving circuit according to the embodiment of the present invention includes a DC-to-DC switching circuit 1, an output overvoltage protection circuit 2, a constant current sampling control circuit 3, and an output current pulse width adjustment circuit 4. And the system enable terminal controls the line 5. Wherein, the input voltage is connected to the DC-DC switch line 1 via a fuse (Fuse), the output overvoltage protection circuit 2, the constant current sampling control line 3, and the output current pulse width adjustment line (ie, pulse width modulation (Pulse) The Width Modulation (PWM) dimming control circuit 4, and the system enable terminal control circuit 5 are connected to the DC to DC switch line 1.

Specifically, the DC-to-DC switching circuit 1 includes an input filter capacitor C1, a boost inductor L1, a boost diode D1, an output voltage filter capacitor C2, and a wafer control circuit 1-1. The wafer control circuit 1-1 includes a PWM control chip (specifically shown as OB3352 in FIG. 1) and peripheral components matched thereto.

As shown in Figure 1, the PWM control chip includes 8 function pins, as follows: System loop compensation pin (COMP pin), grounded via system loop compensation capacitor C _CMP and system loop compensation resistor R _CMP ; The control signal input pin (ENA pin) is directly connected to the line system enable terminal control line 5; the dimming signal input pin (PWM pin) is directly connected to the output current pulse width adjustment line 4; the metal oxide semiconductor field effect transistor The driving pin (GATE pin) is connected to the metal oxide semiconductor field effect transistor (MOSFET) Q1 included in the DC to DC switching circuit 1 for driving the metal oxide semiconductor field effect transistor Q1; the grounding pin (GND pin) , chip reference ground; peak current sampling input pin (CS pin), grounded via sampling resistors R _CS2 and R _CS1 for input of MOSFET peak current sampling; output current setting pin (FB pin), through resistor R _FB1 and constant current The sampling control circuit 3 forms an output current setting function when connected; and forms an output overvoltage protection function when connected to the output overvoltage protection circuit 2; the chip internal circuit power supply pin (VIN pin) is used for power supply of the internal circuit of the chip. The VIN pin into voltage is connected to the filter capacitor C _VIN after filtering.

In addition to this basic function, the DC-to-DC switch line 1 is connected to the constant current sampling control line 3 to form a dimming line. The overvoltage protection line 2 provides a sampling signal through the voltage dividing resistors R _OVP1 and R _OVP2 , and realizes an output overvoltage protection function after reaching the threshold of the regulator Z1. The output current setting pin (FB pin) of the PWM control chip controls the output current by connecting the resistor R _FB . The output current pulse width adjustment circuit 4 is an external PWM dimming control circuit, and the output current can be adjusted by adjusting the pulse width of the input signal (the external low frequency PWM signal is input to the PWM pin of the PWM control chip through the resistor R _DIM . The system enable terminal control Line 5 controls the operating state of the PWM control chip through an external high and low level (the external control signal is input to the ENA pin of the PWM control chip through the resistor R _ENA ).

Figures 2A and 2B show two connection modes of the LED string shown in Figure 1 : multiple strings of LED loads and single string of LED loads. Among them, the single-string LED can directly achieve constant current and current regulation through the constant current sampling control line 3. The multi-string LED can first realize the current constant and current regulation by self-adjusting the discrete current sharing line and then through the constant current sampling control line.

For the DC-to-DC constant current driving circuit according to the embodiment of the present invention, the PWM signal outputted by the output current pulse width adjusting circuit 4 is used to control the pulse width of the output current, thereby achieving accurate current control. In addition, the DC-to-DC constant current driving circuit according to the embodiment of the present invention can provide effective protection for an abnormality such as an open load that is common to a load circuit such as an LED light string.

The present invention has been described above with reference to the specific embodiments of the present invention, but those skilled in the art will understand that various modifications, combinations and changes may be made to the specific embodiments without departing from the scope of the claims or the equivalents thereof. The spirit and scope of this creation.

1‧‧‧DC to DC switch circuit

2‧‧‧Output overvoltage protection circuit

3‧‧‧Constant current sampling control circuit

4‧‧‧Output current pulse width adjustment circuit

5‧‧‧System enable control line

C1‧‧‧ input filter capacitor

C2‧‧‧Output voltage filter capacitor

D1‧‧‧Boost diode

L1‧‧‧Boost Inductance

1-1‧‧‧ wafer control circuit

Q1‧‧‧Metal Oxide Semiconductor Field Effect Transistor

Z1‧‧‧ Voltage Regulator

Fuse‧‧‧Fuse

C _CMP ‧‧‧ system loop compensation capacitor

R _CMP ‧‧‧ system loop compensation resistor

R _CS1 , R _CS2 ‧‧‧Sampling resistor

C _VIN ‧‧‧Filter Capacitor

R _OVP1 , R _{OVP2 ‧‧‧voltage} resistor

R _FB , R _FB1 , R _DIM , R _ENA ‧ ‧ resistance

Claims (3)

A DC-to-DC constant current driving circuit includes a DC-to-DC switching circuit, an output overvoltage protection circuit, a constant current sampling control circuit, an output current pulse width adjustment circuit, and a system enable terminal control circuit, wherein the DC to DC The switch circuit includes a wafer control circuit, wherein the pulse width modulation control chip in the wafer control circuit comprises: a system loop compensation leg, a ground compensation capacitor and a system loop compensation resistor ground; a wafer enable control signal An input pin connected to the system enable terminal control line; a dimming signal input pin connected to the output current pulse width adjustment line; a metal oxide semiconductor field effect transistor drive pin, and the DC to DC switch line a metal oxide semiconductor field effect transistor connection included; a ground pin, a wafer reference ground; a peak current sampling input pin grounded via a sampling resistor; an output current setting pin, and the constant current sampling control line and the output overvoltage Protection circuit connection; and chip internal circuit power supply pin, input voltage is filtered by filter capacitor Chip connected to the internal circuitry foot. The DC-to-DC constant current driving circuit according to claim 1, wherein the DC-DC switching line and the constant current sampling control line are connected to form a dimming line. The DC-to-DC constant current driving circuit according to claim 1, wherein the DC-DC switching circuit includes a boosting inductor and a boosting diode, in addition to the chip control circuit. And an output voltage filter capacitor.