Sawtooth wave generating circuit with high cost performance

Abstract

The embodiment of the utility model discloses a sawtooth wave generating circuit with high cost performance, which comprises an MCU (Microprogrammed Control Unit), a charge-discharge capacitor, a switch tube and a constant current source for outputting constant current, the output end of the constant current source is connected with one end of the charge-discharge capacitor and the drain electrode of the switch tube, the other end of the charge-discharge capacitor and the source electrode of the switch tube are grounded, and the MCU is connected with the grid electrode of the switch tube. According to the utility model, the required elements are few, and the cost performance is high. The frequency can be adjusted through the single-chip microcomputer, the sawtooth wave amplitude can be adjusted through the resistor R1 and the resistor R2, and debugging is easy.

Description

Technical Field

[0001] The utility model relates to the technical field of control circuits, in particular to a sawtooth wave generating circuit with high cost performance. Background Art

[0002] Most of the traditional frequency adjustable sawtooth wave generating circuits are composed of multiple operational amplifiers, MCU or 555 timer and other circuits. Such circuits are costly, complex and difficult to debug. Utility Model Content

[0003] The technical problem to be solved by the embodiments of the utility model is to provide a sawtooth wave generating circuit with high cost performance, so as to simplify the circuit and reduce the cost.

[0004] In order to solve the above technical problems, an embodiment of the utility model proposes a cost-effective sawtooth wave generating circuit, including an MCU, a charging and discharging capacitor, a switching tube, and a constant current source that outputs a constant current, wherein the output end of the constant current source is connected to one end of the charging and discharging capacitor and the drain of the switching tube, the other end of the charging and discharging capacitor and the source of the switching tube are grounded, and the MCU is connected to the gate of the switching tube.

[0005] Furthermore, the constant current source includes a resistor R1, a resistor R2, a resistor R3 and a PNP transistor Q1, the c-pole of the PNP transistor Q1 is connected to one end of the charging and discharging capacitor and the drain of the switching tube, the e-pole and the b-pole of the PNP transistor Q1 are respectively connected to one end of the resistor R1 and the resistor R2, the other ends of the resistor R1 and the resistor R2 are externally connected to the power supply end, and the two ends of the resistor R3 are respectively grounded and connected to the b-pole of the PNP transistor Q1.

[0006] Furthermore, the constant current source further includes a capacitor C1, and the capacitor C1 and the resistor R2 are connected in parallel.

[0007] Furthermore, it also includes a resistor R4 and a resistor R5, and the gate of the switch tube is connected to the MCU and the ground through the resistor R4 and the resistor R5 respectively.

[0008] The beneficial effects of the utility model are as follows: the utility model requires fewer components and has a high cost performance ratio. The utility model can adjust the frequency through the single chip microcomputer, and can adjust the sawtooth wave amplitude through the resistors R1 and R2, and the debugging is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a structural schematic diagram of a cost-effective sawtooth wave generating circuit according to an embodiment of the utility model.

[0010] Figure 2 It is a current diagram of a cost-effective sawtooth wave generating circuit according to an embodiment of the utility model.

[0011] Figure 3 It is a sawtooth waveform diagram produced by the embodiment of the utility model. DETAILED DESCRIPTION

[0012] It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present utility model is further described in detail below in conjunction with the drawings and specific embodiments.

[0013] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back, etc.), they are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0014] In addition, in the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0015] Please refer to Figure 1 to Figure 3 The sawtooth wave generating circuit with high cost performance of the utility model embodiment includes MCU, charging and discharging capacitors, switch tubes and constant current source outputting constant current. Nmos tube Q2 is used as the switch tube, and C2 is the charging and discharging capacitor.

[0016] The output end of the constant current source is connected to one end of the charge and discharge capacitor and the drain of the switch tube, the other end of the charge and discharge capacitor and the source of the switch tube are grounded, and the MCU is connected to the gate of the switch tube. The gate of the switch tube is tested for voltage, and it can be turned on. The MCU controls the on / off of the switch tube by outputting high / low level, and then realizes the sawtooth wave by controlling the constant current source to charge and discharge the capacitor.

[0017] As an implementation method, the constant current source is a uA-level constant current source, including a resistor R1, a resistor R2, a resistor R3, a capacitor C1, and a PNP transistor Q1. The c-pole of the PNP transistor Q1 is connected to one end of the charging and discharging capacitor and the drain of the switch tube, the e-pole and the b-pole of the PNP transistor Q1 are respectively connected to one end of the resistor R1 and the resistor R2, the other end of the resistor R1 and the resistor R2 are externally connected to the power supply end, and the two ends of the resistor R3 are respectively grounded and connected to the b-pole of the PNP transistor Q1. The capacitor C1 and the resistor R2 are connected in parallel.

[0018] As an implementation method, the cost-effective sawtooth wave generating circuit further includes a resistor R4 and a resistor R5, and the gate of the switch tube is connected to the MCU and the ground through the resistor R4 and the resistor R5 respectively.

[0019] The working principle of this utility model: Figure 2The base voltage of the PNP transistor Q1 is [VDD / (R2+R3)]*R2, so the voltage across R1 is clamped to VDD-[VDD / (R2+R3)]*R2-Vbe. Because the collector load of the transistor Q1 does not affect the voltage across R1, the collector of the transistor Q1 outputs a constant current, and the current is {VDD-[VDD / (R2+R3)]*R2-Vbe} / R1.

[0020] The relationship between the current and voltage of capacitor C2 is I=Cdu / dt, where I and C are constants, and the change in voltage across the capacitor over time is a constant, meeting the conditions for forming a sawtooth wave.

[0021] Figure 2 In the example, VDD is 10V, R1 is 41K, R2 is 3.3K, R3 is 15K, R4 is 100R, R5 is 10K, C2 is 1nF, C1 is 100nF, and the MCU IO port sends a square wave with a period of 170uS and a pulse width of 1.2uS. The resulting sawtooth waveform is as follows: Figure 3 shown.

[0022] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cost-effective sawtooth wave generating circuit, characterized in that: It includes an MCU, a charging and discharging capacitor, a switching tube, and a constant current source that outputs a constant current. The output end of the constant current source is connected to one end of the charging and discharging capacitor and the drain of the switching tube, the other end of the charging and discharging capacitor and the source of the switching tube are grounded, and the MCU is connected to the gate of the switching tube.

2. The cost-effective sawtooth wave generating circuit as claimed in claim 1, characterized in that: The constant current source includes resistors R1, R2, R3 and PNP transistor Q1. The c pole of the PNP transistor Q1 is connected to one end of the charging and discharging capacitor and the drain of the switching tube. The e pole and b pole of the PNP transistor Q1 are respectively connected to one end of the resistor R1 and the resistor R2. The other ends of the resistor R1 and the resistor R2 are externally connected to the power supply end. The two ends of the resistor R3 are respectively grounded and connected to the b pole of the PNP transistor Q1.

3. The cost-effective sawtooth wave generating circuit as claimed in claim 2, characterized in that: The constant current source further includes a capacitor C1, and the capacitor C1 and the resistor R2 are connected in parallel.

4. The cost-effective sawtooth wave generating circuit as claimed in claim 1, characterized in that: It also includes a resistor R4 and a resistor R5. The gate of the switch tube is connected to the MCU and the ground through the resistor R4 and the resistor R5 respectively.

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